progress at lampf - ipen

Progress at LAMPFJanuarys-December 1985

Clinton P. Anderson

Meson Physics Facility

Los Alamos, National Laboratory

LA-10738-PR

Progress Report

T ' P A'orici 3 i:r'jt obser-.ation ot scat-ter ^g ot e'ectton neutrinos by elec-trons /.asmadeatLAMPFm 1985i seep 18) The cover shows acuta.<\ay -':e« of the neutrino detectorT'le active cosmic-ray veto system(purple) consists ot 594 multiwirepfooortional counters (MVVPCs) ar-ranged as shown in four layers cover-ing the walls and roof, with one addi-tional layer on the flooi; each counterhas eight triangular sections Thecentral detector is a 40-layer sand-wich of alternating scmtillatorcounters and flash-chamber modulesiFC'vls) The 160 scintillator countersweigh 9 5 tons, and the 208 000tubes ol the FCMs, m alternatinghorizontal and vertical orientation asshown, weigh 4 5 tons In the figurethe scintillator counters are pale blue,flash chambers are shown as whitelayers m the central detector sand-wich

- • > , .

DISCLAIMER

This report was prepared as an account of work sponsored by an agency ol the L ailed StaleGovernmenl. Neither the Uniltd States Government nor any agencv thereof, nor ,in> u' ihcemployees, makes any warranty, express or implied, or assumes any legal liability ->r re: winbihty for llie accuracy, completeness, or usefulness of any information, apparatus, produ.t,process disclosed, or represents that its use would not infringe privately owned rights. Kek:ence herein to any specific commercial product, process, ur service by uade name, trademark,manufacturer, or otherwise does not necessarily constitute or imply Us endorsement, rec.tm-mendation, or favoring by the United Stales Governmenl or any agency thcreol The m:wsand opinions >.i\~ authors expressed herein do nol necessarily stale or relxcl lh<>se ul iheUnited Stales Government or any agency thereof.

LA—10738-PR

DE86 014891

Progress at LAMPFLA-10738-PRProgress Report

UC-28Issued: May 1986

EDITORS

John C, Allred

Beverly Talley

SCIENTIFIC EDITORIAL BOARD

Olin B. van Dyck

Richard L, Hutson

Mario E. Schillaci

DESIGN

JeffSegler

INFRARED PHOTOGRAPHY

Jeff Cannon

Mick Greenbank

PRODUCTION

Lois Rayburn

Chris Weaver

ABSTRACT

'' Progress at LAMPF'' is the annualprogress report of MP Division of the LosAlamosNationaltaboratory. Ibrief reports on research done ,f'by researchers frcra p t h e y q fother.Los-AlamosDivisiB

DISTRIBUTION OP THIS DOCUMBa IB WU.

PROGRESS AT LAMPF

FOREWORD The p:iM year lias been one of great excitement and change both here atl.AMl'l' and at Los Alamos National Laboratory. Louis Rosen stepped aside asDirector of l.AMPF on November 11, 19HS,and I took over thai very challeng-ing assignment. Don Kerr resigned as the Los Alamos National LaboratoryDirector on October I, I98S, and Sig flecker, an outstanding metallurgist andformer Director ol I he Center lor Materials Science, was selected by adistinguished search committee to be our next Laboratory Director, ile willbe an understanding and strong advocate of basic research.

LAMPF has had an outstanding record of reliable and effective operationwhile delivering the most intense proton beam anywhere in the world.Hence, in the search for a new leader for the Medium linergy Physics Division(Ml1), it was only natural to turn to a person who was greatly responsible forthis excellent record. So it was thai Don Hagerman was selected by LosAlamos management 10 be the new MP Division Leader. He and I will bev. rking closely over the coming years to continue to provide the environment and hardware required for a world-class research program.

The research output over the past year was outstanding. Among thehighlights were results from lixp. 225, the world's first observation of theinterference between the neutral and charge-changing weak currents. Thepresent results are consistent with the Standard Model and, after an additionalyear of running, the results will further test the Standard Model. A new andvery strong lower limit has been placed on the lepton family number violatingrare decay of the muon into an electron and a photon and the 7t,r) reaction hasbeen observed for the first time on a variety of nuclei.

With regard to new facilities and large experiments, we are firmly com-mitted to proceeding with the upgrade of the Nucleon Physics Laboratory.This upgrade will provide unparalleled opportunities for our users to investi-gate the spin and isospin dependence of nucleonnucleon and nucleon-

vi

PROGRESS AT LAMPF

nucleus interactions. A third generation rare decay experiment involving 10n.Mitiuions is also jusi getting underway. We all share a real sense of pride ini IK- rapid commission ing of the Proton Storage Ring (PSR), which reached.-in (.iA. or nae third of its design intensity, within die first h months ofoperation. The pulses of ihe proions from PSR are used to produce a source ofpulsed neutrons for studies of the structure of materials both physical andbiological. The pulsed neutron facility is referred to as ihe Los AlamosNeutron Scattering Center t LANSCEK

In addition to the facilities and experiments, LAMP!" serves as a center forthe discussion and development of new and significant concepts in mediumenergy physics. We held <> workshops and a summer school at which some Si)graduate students were exposed to the frontiers of nuclear theory. It wasintellectually stimulating and shows the intellectual attraction of the frontiersof our suhject to young scientists.

The foreword would not be complete without mention of developmentssurrounding our plans for an advanced hadron facility. We will soon becirculating an update of our proposal of December 198-t. Considerableadvances have been made in even' aspect of that original proposal. Thephysics case has been greatly strengthened, particularly with regard to stronginteraction research. A viable and cost-effective machine design is now morecertain and new ideas for producing secondary beams of greater intensity andflexibility have been developed. Thus, our new plan will show higherintensity secondary beams and lower cost. The actual funding to construct anylarge facilities in basic research remains highly uncertain while the UnitedStates deals with the issues surrounding the large federal deficit.

Gerald T. GarveyDirector of LAM PF

vii

PRQfiRESS AT LAMPF

CONTENTS Experimental Areas

LAMPFNews 1Rosen Steps Down 2New LAMPF Director 3New MP-Division Leader 4

LAMPF Users Group 7Nineteenth Annual Meeting 8Committees 9Minutes 12Workshops 13Visitors Center 14

Research 17Nuclear and Particle Physics 18

E-'PERIMEI IT 225 — t leutrmo -rea

A Study of Neutrino-Electron Elastic Scattering 18

Cygnus Cosmic-Ray Air-Shower Array 24

E.'PERIMEtn 65" - EPICS

Pion Inelastic Scattering from the N= 28 Isotones andNeighbors 26

E/ PEM/lE! ITS ™ yna 906 - EPICSPion Double-Charge-Exchange Angular Distributions for

T= 2 Double-Isobaric-Analog States 27

E'PERiUEMTr;^"" ~so and826 — EPICS

Mass Dependence of Pion Double Charge Exchange 29

i,- PEPtf.C: IT 800 — EPiCG

Inelastic Pion Scattering from "Ne 33

r -t•[ Hit/iF!,rs~P>.) •-EFi'.'r.

Large Angle Excitation Functions for Elastic Scatteringof 71* from I2C and "'O 34

t -^tHiMEl 11 8 -6 - - t"f-"C3Energy Dependence of Pion Scattering to the

Giant Resonance Region of 2""Pb 38

E- PERIMEr IT 905 — EPICSNew Test of Superratio by 71* Elastic Scattering

on3Hand3He 40

E-.PERIMENT392 — HRSMeasurement of the WoH'enstein Parameters iotp + p

and p + n Scattering at 500 and 800 MeV

f-PERIUHlToSh MRSM e a s u r e m e n t of T h i r d - O r d e r Sp in O b s e r v a b l e s

tor E l a s t i c / W Scat te r ing at 800 MeV . . . 47

Measurement of Cross Sections and Analyzing Powersfor Elastic and Inelastic Scattering of400 to 500 MeV Protons iVom "C 52

E - ' r c ^ . ! E M T " 4 ! -• HR:.,

Continuum Polarization Transfer in 500 MeVProton Scattering and Pionic Collectivity in Nuclei . . . 53

r . - r — K i p j T '..-a _ _ H R S

Characteristic Dirac Signature in Large-AngleElastic Scattering at 500 MeV 56

Development of a oJ Focal-Plane Polarimeter at HRS 58

Continuum Spin-Flip Cross Section Measurementsfrom'"Ca 60

Measurement of the £2 Resonance Effect in Pionic Atoms . . 62

Pion Charge Asymmetries for 1?C at Low Beam Energieson the LEP Spectrometer 74

Pion Double Charge Exchange on UCat Low Energies 76

E.-PFril'/E'ii Til - Lt-Study of the Mass Dependence of Pion

Single Charge Exchange at 20 MeV. 85

E/PERIMEMT 899 — LEPAngular Distributions for the 165Ho(7i+,7t°) l65Er Reaction

to the Isoharic-Analog State at 100, 165, and 230 MeV 89

PROGRESS AT LAMPfContents

tx

PROGRESS AT LAMPF

ontents

Search for Neutrino Oscillations at LAMPF 92

P . p rp iN jp t r ! ' •. .'!«-( '•-,{ i <w) -u 'n j ufi;" . p*

.1 Dependence of Inclusive Pion Double Charge Exchange . 96

LxPLRlMt i l l 804 PJ t.isiMeasurement of the Analyzing Power in iCf> —- yn

and 7i~p—* rc"/( LIsing :s Transversely Polarized Target . . . 100

EXPERIMENT 8J." - PJ

Study of Isobaric-Analog-State Transitions withPion Single Charge Exchange in the300- to SOO-MeV Region 106

EXPERIMENT 852 — P3

Measurements of (n^Ti) Reactions on Nuclear Targetsto Study the Production and Interactionof T| Mesons with Nuclei 110

EXPERIMENT 888 — SMC

Study of the Decay Jt+— e+vey 113

EXPERIMENT 969 — SMCMEGA: Search for the Rare Decay u+ — e+y 114

EXPERIMENT 914 — SMC (LAMPF)EXPERIMENT 791 — Beam B5 (Brcokhaven)

Study of Very Rare KL Decays 122

EXPERIMENT 745 — SMCE2 and E4 Deformations in 232Th, iw^w^v,

and2i9.24O.242pu ^ g


A Search for the CNoninvariant Decay 7t° — 3y 129

EXPERIMENTS 400/445 — SMCCrystal Box Experiments 131

Atomic and Molecular Physics 134Theory of Muon-Catalyzed Fusion 134

EXPERIMENT 727 — Biomed and SMC

Measurement of the Efficiency of Muon Catalysis inDeuterium-Tritium Mixtures at High Densities 142

PROGRESS ATJ.AMPFContents

Materials Science 150L-M. HIVIRil H4_' • ;K'K"

Muon Spin Relaxation and Knight-Shift Studies ofItinerant Magnets and Heavy Fermion Materials ISO

t ' P I MlMf t i l : ; i i J ^ i a r i d ft>l - ' !IVV.~

Muon-Spin Relaxation (uSR) in Select Magnetic Oxidesand Oxide Spin Glasses 157

y-41 SMC

Muon Spin-Relaxation Studies (u.SR) ofDisordered Spin Systems l6l

Improvements to the Muon-Spin Relaxation (uSR)Experimental Facility 165

EXPERIMENT 787 - BiomedM u o n C h a n n e l i n g f o r S o l i d - S t a t e P h y s i c s I n f o r m a t i o n . . . . 1 6 6

Radiation-Effects Studies 172Operating Experience at the Los Alamos Spallation

Radiation-Effects Facility (LASREF) at LAMPF 172

EXPERIMENT 769 — Beam Stop AreaProton-Irradiation Effects on Candidate Materials for the

German Spallation Neutron Source (SNQ) 173Quantitative Study, by Field-Ion Microscopy, of

Radiation Damage in Tungsten After Neutronand Proton Irradiation 174

EXPERIMENT 936 — Radiation Damage

Additional Measurements of the Radiation Environmentat the Los Alamos Spallation Radiation-EffectsFacility (LASREF) at LAMPF 175

EXPERIMENT 943 — Radiation Damage

Microstructural Evolution Under Particle Irradiation 176

Biomedical Research and Instrumentation 178Radiobiology of Ultrasoft X Rays 178Instrumentation 179

Nuclear Chemistry 180EXPERIMENT 897 — LEP

Pion Single Charge Exchange in 7Li to theIsobaricAnalog Ground State of 7Be 180

XI

PROGRESS AT LAMPF

Contents

E-PERIMLNT 752 — l"hm 1 aiget AreaTime-of-Flight Isochronous (TOFI) Spectrometer 184

Radioisotope Production 190Isotope Production and Separation 19"Radiophannaceuiicai usnciiiig Re.-;-•'!•-:; , YjbRadioisotope Production Publications 200

Theory 204Nonanalog Pion Double Charge Exchange

Through the A33-Nucleon Interaction 204Theoretical Evidence for the Existence of the

T)-Mesic Nucleus 205A Self Consistent Calculation of OneGluon Exchange

in the Friedberg-Lee Soliton Model 208The Pion-Nucleon System at Low Energy 211Report of the T-5 Theoretical Group 220

MP-Division Publications 232

Status of LAMPF II 249Accelerator Studies 250

Facility Development 261Nucleon Physics Laboratory (NPL) Upgrade 262Spectrometer Calibration at EPICS 269Radiation-Effects Facility 272Data-Analysis Center 277LAMPF Computer-Control System 279

Accelerator Operations 283

Milestones 287

Appendixes 295Appendix A:

Experiments Run in 1985 296

Appendix B:New Proposals During 1985 303

Appendix C:LAMPF Visitors During 1985 311

Informatten far Contributors 317

Xll

PROGRESS AT LAMPF

Experimental Area

LAMPF Experimental Areas

AREA C

IN

i10 20 30

I l lMETERS

ISOTOPEPRODUCTION &RADIATIONEFFECTS

LINE E

! LEP\ \ T E S T\\ BEAM / ~ \

TOFI " SMCNEUTRINO

AREA

CHANNELSEPBLEPP3

SMC

External Proton Beam ChannelLow-Energy Pion ChannelHigh-Energy Pion ChannelStopped-Muon Channel

SPECTROMETERSEPICS Energetic Pion Channel and SpectrometerHRS High-Resolution SpectrometerTOFI Time-of-Flight Isochronous Spectrometer

FACILITIESNPLPSR

NEUTRINOEXPEF-'MENT

SERVICEBUILDING

BEAMS

Protons or H'

_ _ _ _ _ Polarized protonsorH"

Mesons (n or |i)

Neutrinos (v)

Neutrons

Mucleon Physics LaboratoryProton Storage Ring

LANSCE Los Alamos Neutron Scattering Center(WNR, Weapons Neutron Research Facility)

xiv.

LAMPF News

Rosen Steps Down

New LAMPF Director

New MP-Division Leader

IMMTHEWS

Rosen Steps Down

Rosen Steps Down

At the November LAMPF UsersMeeting, it was announced that LouisRos<_. will be succeeded by GeraldGarvey as LAMPF Director. Garveycontinues as a Deputy Associate Di-rector of Los Alamos National Labora-tory. Rosen has been named a SeniorFellow of the Laboratory, a positionthat will enable him to pursue severalinterests that follow from a lifetime ofactivities in science and public inter-est.

After teaching physics at the Uni-versity of Alabama and PennsylvaniaState University, Louis Rosen joinedthe Manhattan Project in Los Alamos

in 1944. Following World War II,Rosen divided his time betweenbasic research in nuclear physics andnational defense activities. At Los Al-amos he has held the position ofgroup leader of the nuclear micro-scopy laboratory, alternate divisionleader of the experimental physicsdivision, and division leader of theMedium-Energy Physics Division.

Rosen was a pioneer in the devel-opment and exploitation of tech-niques for neutral- and charged-particle detection. From this workemerged a clearer understanding ofthe mechanism of neutron interac-tions and the first clear evidence thata controlled thermonuclear reactor,operating on the dt cycle, might pro-duce more tritium than it consumes.His work gave rise to better phenom-enological potentials for describingand predicting nucleon-nucleus in-teractions and for placing betterlimits on the validity of microscopicreversibility in nuclear reactions. Hewas responsible for measuring manyof the neutron cross sections in thedesign of the first thermonuclearweapons.

In 1963 he received the E. O. Law-rence award for these activities fromthe U.S. Atomic Energy Commission.Other honors include Sesquicentennial Honorary Professor at the Uni-versity of Alabama, PennsylvaniaState Alumni Fellow, and Universityof New Mexico Honorary Doctor ofScience.

LAMPF HEWS

! low LAMPF Director

In 1962 Posen initiated the mesonfactory proposal at Los Alamos.Under his leadership LAMPF becamethe largest nuclear science facility inthe world. In addition to promotingbasic research, Rosen saw that ac-celerator beams and technology weremade to serve the immediate publicinterest through production of betterradioisotopes for industry andmedicine, the study of radiation damage in reactor materials, and cancertherapy.

Rosen is active in the affairs ofscience and in providing advice onscientific matrers to the federai estab-lishment. He served as a member ofthe National Accelerator Panel on theFuture of Nuclear Science, on thepanel to recommend a managementstructure for the administration of theOrbiting Space Telescope Project,and as a member of a committee toadvise the General Accounting Of-fice on ground rules for an in-depthaudit of high-energy physics. In theAmerican Physical Society (APS), hewas Chairman of the Division of Nu-clear Physics in 1985. He has alsoserved as a member of the APS Coun-cil and as Chairman of the Panel onPublic Affairs. He currently serves on

.the USA-USSRJoint Committee forCollaboration on the FundamentalProperties of Matter and continues tosupport the role of science as a chan-nel for international understanding.

Gerald GarveyNew LAMPF Director

New LAMPF Director Gerald T.Garvey joined the Laboratory in 19H4as Deputy Associate Director for Nu-clear and Particle Physics ProgramsHe came to Los Alamos from ArgonneNational Laboratory in Illinois, wherehe was also a professor at the Univer-sity of Chicago. He has taught atPrinceton, Oxford, and Yale Univer-sities, and he has been a visiting lec-turer at the Weizmann Institute inIsrael.

Garvey received his doctorate fromYale University and his under-graduate degree from Fairfield Uni-versity, Fairfield, Connecticut.

Garvey is currently an editor of An-nual Review of Nuclear and ParticleScience (since 1982) and of Com-ments on Nuclear and Particle Phys-ics (since 1984). He was editor ofPhysics Reports from 1976 to 1979.

Garvey has served on program ad-visory committees at Nevis, IndianaUniversity, and LAMPF. He is a mem-ber of the Visiting Committee of thePhysics Department at SUN Y,Sconybrook, and has served in asimilar capacity at the University ofRochester.

LAMPF NEWSNew MP Division leader

He is presently a member of theAdvisory Committee for Physics ofthe National Science Foundation andis chairman of its subcommittee toreview NSF's Nuclear Science Pro-gram. He was a member of the HighEnergy Advisory Committee atBrookhaven National Laboratory,1979-1983; the Review Committee forthe Nuclear Science Division at Law-rence Berkeley Laboratory,1981 1984; and the Review Committee on TRIUMF of the National Re-search Council of Canada, 1983-1984.

Garvey served on the LivingstonPanel on Future Electron Ac-celerators, 1977; the Committee onthe Future of Nuclear Science of theNational Academy of Sciences,1976-1977; and the DOE/NSF Nu-clear Science Advisory Committee(NSAC), 1977-1980.

Of his successor, Rosen said, "Wewere fortunate to recruit someone ofGarvey's competence, knowledge,and scientific reputation."

Since 1962, he has played a keyrole in the design, construction,scheduling, operation, and upgradesof LAMPF—a half-mile-long ac-celerator that has emerged as aworld-class research center.

Hagerman received a bacnelor'sdegree in physics (magna cumlaude) from the University of Colo-rado in 1951. Four years later heearned a doctorate in physics fromStanford University.

A Fellow of the American PhysicalSociety, he has served as a member ofthe Department of Energy/NationalScience Foundation/Nuclear ScienceAdvisory Committee.

In 1983 he was a visiting scientistat MIT and a visitor at the IndianaUniversity Cyclotron Facility.

Don HagermanNew MP-Dlvlslon Leader

Don Hagerman was appointedApril 7,1986, to lead the Medium-Energy Physics Division. The an-nouncement, which followed a na-tionwide search launched earlier thisyear, was made byjohn Browne, As-sociate Director for Research.

Hagerman became a staff memberat Los Alamos in 1955, conductingresearch on controlled thermonu-clear reactions.

LAMPF NEWS

LAMPF Users Group

Nineteenth Annual Meeting

Committees

Minutes

Workshops

Visitors Center

IAMPF USERS 6R0UP

Annual Meetmq

Nineteenth Ann^ i f u

The Nineteenth Annual Meeting ofthe LAMPF Users Group, Inc., washeld in Los Alamos on November 4 5,1985, with 172 attendees. ChairmanRobert Redwine (MIT) presided atthe first session, which included awelcoming address by Robert Thorn,Acting Laboratory Director, and a Re-port from Washington by David Hen-drie (Department of Energy). TheLAMPF Status Report was presentedby Louis Rosen, and Gerald Garveyspoke on Future Directions ofLAMPF. The LAMPF operations re-port was delivered by DonaldHagerman.

In the afternoon session, conducted by incoming Chairman BarryPreedom (University of South Caro-lina), Robert Redwine gave the An-nual Users Group Report, which wasfollowed by a presentation of theelection results. June Matthews(MIT) is Chairman-Elect of the Boardof Directors; new members areCharles Goodman (Indiana Univer-sity) and Gerald Hoffmann (Univer-sity of Texas).

The following talks were givenduring the meeting:

"A Vp-e Proposal for LAMPF,"Hywel White (Brookhaven);

"Searching for Muon NumberViolation at LAMPF: Current Re-sults and Future Prospects,"Martin Cooper (Los Alamos);

"NPL Upgrade," John McClelland(Los Alamos);

"The WNR Neutron Source," PaulLisowski (Los Alamos);

"New High-Resolution 710 Spec-trometer," David Bowman (LosAlamos);

"Japanese Medium-Energy Pro-gram," Toshimitsu Yamazaki(University of Tokyo); and

"LAMPF II," Henry A. Thiessen(Los Alamos).

LAMPF USERS 6H0UP

Committees

Ccmmlitees

Board of Directors

The Board of Directors comprises aSecretary/Treasurer and seven memhers elected by the LAMPF UsersGroup, Inc., whose interests they represent and promote. They concernthemselves with LAMPF programs,policies, future plans, and especiallywith how users are treated at LAMPF.Users should address problems andsuggestions to individual Boardmembers.

The Board also nominates newmembers to the Program Advisory'Committee (PAC).

The 1986 membership and termexpiration dates are listed below.

James Bradbury(Secretary/Treasurer)

Los Alamos

Terms Expiring in 1986Robert Redwine

(Pasi Chairman)MIT

George BurlesonNew Mexico State University

Donald GeesamanArgonne National Laboratory

Terms Expiring in 1987Barry Preedom (Chairman)University of South Carolina

Charles GoodmanIndiana University

Gerald HoffmannUniversity of Texas

Terms Expiring in 1988June Matthews

(Chairman-Flea)MIT

Technicai Advisory Panel

The Technical Advisory Panel(TAP) provides technical recommen-dations to the Board of Directors andLAMPF management about the development of experimental facilities andsupport activities. The TAP has12 members, appointed by the Boardof Directors for 3-year staggeredterms; the Chairman of the Board ofDirectors also serves as TAP chairman. The TAP membership and termexpiration dates are listed below.

Terms Expiring in 1985Harold A. EngeMIT

Richard HutsonLos Alamos

Christopher L. MorrisLos Alamos

Thomas A. RomanowskiOhio State University

Terms Expiring in 1986William BriscoeGeorge Washington University

Michael A. OothoudtLos Alamos

Gary SandersLos Alamos

Charles A. WhittenUCLA

LAHPF USERS GROUP

Committees

Terms Expiring in 1987David BowmanLos Alamos

Gerald HoffmannUniversity of Texas

RoyJ. PetersonUniversity of Colorado

Robert E. PollockIndiana University

1AMPF Program AdvisoryCommittee

The Program Advisory Committee(PAC) comprises about 25 membersappointed for staggered 3-year terms.Members advise the Director ofLAMPF on the priorities they deemappropriate for the commitment ofbeam time and the allocation of re-sources for the development of ex-perimental facilities. The PAC meetstwice each year for 1 week, duringwhich time all new proposals thathave been submitted at least2 months before the meeting date areconsidered. Old proposals, and thepriorities accorded to them, also maybe reviewed.

Terms Expiring in 1986David AxenTRIUMF

Barry BarishCalifornia Institute of Technology

Dietrich DehnhardUniversity of Minnesota

Frieder LenzSIN

Harold M. Spinka.Jr.Argonne National Laboratory

Vi^or E.Viola, Jr.Indiana University

Larry ZamickRutgers University

Terms Expiring in 1987EricG. AdelbergerUniversity of Washington

Gerard M. CrawleyMichigan State University

William R. GibbsLos Alamos

WickC.HaxtonUniversity of Washington

Stanley B. KowalskiMIT

Philip G. RoosUniversity of Maryland

Benjamin ZeidmanArgonne National Laboratory

Terms Expiring in 1988HallL. CrannellCatholic University of America

10

LAMPF USERS GROUPWorking Groups

DavidJ. ErnstTexas A&M University

James L. FriarLos Alamos

Daniel S. KoltunUniversity of Rochester

Energetic Pion Channel andSpectrometer (EPICS)

Kalvir DhugaNew Mexico State University

High-Energ, Pion Channel (P3)Gordon MutchlerRice University

W. Gary LoveUniversity of Georgia

NorbertT. PorilePurdue University

WillemT. H.VanOersUniversity of Manitoba

D. Hywel WhiteBrookhaven National Laboratory

Working Groups Chairmen

High-Resolution Spectrometer (HRS)Raymond FergersonRutgers University

Neutrino FacilitiesStuart FreedmanArgonne National Laboratory

Stopped-Muon Channel (SMC)Martin CooperLos Alamos

Nuclear ChemistryRobert KrausClark University

Nucleon Physics Laboratory (NPL)Upgrade/Medium-ResolutionSpectrometer

John FaucettNew Mexico State University

Computer FacilitiesKok-Heong McNaughtonUniversity of Texas

Solid-State Physics and MaterialsScience

Robert BrownLos Alamos

Muon-Spin RelaxationMario SchillaciLos Alamos

Low-Energy Pion Channel (LEP)James KnudsonArizona State University

11

LAHPF USERS GROUP

Minutes

Minutes

Board of Directors

The LAMPF Users Group, Inc.(LUG1), Board of Directors (BOD)met on March 10, July 9, and Novem-ber 3,1985. All meetings werechaired by Robert Redwine. Selectedtopics of discussion are providedhe low.

There were 172 registrants for the19H5 Annual Users Meeting. Thepapers presented at the meeting andthe minutes of the workships aregiven in the Proceedings.

The Program Advisory Committee(PAC) met in February and August1985. For these 2 sessions 70 newproposals were received. The break-down follows.

HRS 13EPICS 19LEP 15Nuclear Chemistry 1NPL 5SMC 4P3 6Solid-State Physics and

Materials Science 7

The BOD selected William J.Burger (MIT) as the recipient of theLouis Rosen Prize for 1985 for histhesis "An Experimental Study ofPion Absorption in 58Ni atTK = l6() MeV." Because he was outof the country at the time, the awardwas presented to his advisor, RobertRedwine, and will be forwarded tohim later.

Technical Advisory Panel

The Technical Advisory Panel(TAP) met on February 8 and Novem-ber 6,1985. The chief purpose of theFebruary meeting was to providerecommendations for LAMPF man-agement concerning medium-term(next several years), medium-scale(several million dollars) projects andexpenditures. After hearing a numberof presentations the TAP assignedhighest priorities to (1) adequate fa-cilities and support for data acquisi-tion and analysis, (2) the Medium-Resolution Spectrometer (MRS) onLine B, and (3) the Neutron Time-of-Flight (NTOF) facility on Line B.*

•LAMPi- is fully committed to the Nucleon PhysicsLaboratory upgrade, including the MRS and NTOFfacilities Design and procurement el'orl has begun

12

LAMPF USERS GROUPWorkshops

I

At the November meeting the TAPheard presentations on the status of anumber of projects, including theHigh-Resolution Atomic-Beam fa-cility, the Clamshell spectrometer atthe LEP, the Data-Acquisition Center,the Nucleon Physics Laboratory up-grade, a rare muon decay detectorsystem, a new neutrino-source possi-bility, and LAMPF II.

Workshops

The following workshops arescheduled to be held at LAMPF.

NUCLEAR PHYSICS LABORATORY UPGRADESAND MUON-CATALYZED FUSION

December 16-17,1985

FUNDAMENTAL MUON PHYSICS: ATOMS,NUCLEI, AND PARTICLES

January 20-22,1986

PHYSICS WITH POLARIZED NUCLEARTARGETS

February 6,1986

QUARK/GLUON PHENOMENA IN NUCLEARAND PARTICLE PHYSICS

February 7-8,1986

ANNUAL USERS MEETING

October 27-28, 1986

13

LAMPF USERS GROUPVisitors Center

Visitors Center

During this report period, 450 re-search guests worked on LAMPF-re-lated activities or participated in ex-periments at LAMPF; of these, 132were foreign visitors.

LAMPF Users Group Membership

MembershipNon-LaboratoryLos Alamos National Laboratory.

TOTAL

610182

792

Fields of Interest*Nuclear and Particle PhysicsNuclear ChemistrySolid-State Physics and Materials Science.Theory _Biomedical and Biological Applications -Weapons Neutron ResearchData Acquisition and InstrumentationAdministration, Coordination, Facilities, and Operations.Isotope ProductionLAMPF II

65593

150164155128193

5249

397

These numbers do not add up to total membership because ol multiple interests

Institutional DistributionMembership by Institutions

Los Alamos National LaboratoryNational or Government Laboratories.U.S. UniversitiesIndustryForeignHospitalsNonaffiliated

TOTAL

18281

33831144106

792

14

LAMPF USERS GROUP

Visitors Center

Xu m her of InstitutionsNational or Government Laboratories.L'.S. UniversitiesIndustry

ForeignHospitalsNonatfiliated __

19972780

96

TOTAL __ 238

Regional BreakdownFast

Pennsylvania, New Jersey. Delaware. Washington DC,Massachusetts, New York, Connecticut, Vermont,Rhode Island, New Hampshire, Maine

MidwestOhio, Missouri, Kansas, Indiana, Wisconsin, Michigan, Illinois,North Dakota. South Dakota, Nebraska, Iowa, Minnesota

SouthMaryland, Virginia, Tennessee, Arkansas, West Virginia,Kentucky, Nor'h Carolina, Alabama, Mississippi, Louisiana,Georgia, Florida

Southwest, MountainMontana, Idaho, Utah, Wyoming, Arizona, Colorado,New Mexico (excluding Los Alamos), Oklahoma, Texas

WestAlaska. Hawaii, Nevada, Washington, Oregon, California

ForeignLos Alamos National Laboratory

TOTAL

102

94

70

113

86145182

792

15

Mickijeeri&anJ-,

Research

Nuclear and Particle Physics

Atomic and Molecular Physics

Materials Science

Radiation-Effecio Studies

Biomedical Research and Instrumentation

Nuclear Chemistry

Radioisotope Production

Theory

MP-Division Publications

RESEARCHNuclear and Particle Physics

NUCLEAR AND PARTICLE PHYSICS

EXPERIMENT 225 — NeutrinoArea

A Study of Neutrino-Electron ElasticScattering

Univ of California at Irvine. Los Alamos,Univ of Maryland

Spokesman: H. H. Chen (Univ. 0/ California,Irvine)

Bob Burman (MP-4) and Danny Krakauer(University ol Maryland) with central de-tec.or used m Exp 225 (see illustrationon lacing page)

Using the intense 0- to 53-MeVneutrino beam from the LAMPFLine A beam stop, a collaborationfrom the University of California atIrvine, Los Alamos, and the Univer-sity of Maryland has made the firstobservation of ve + e~ —-ve + e~elastic scattering. Measurement ofthis purely leptonic weak reactionprovides a sensitive experimental testof the structure of the electruweakinteraction.

The currently popular theories offundamental forces are gauge the-ories. Within these theories thegravitational, the electromagnetic,and the strong and weak nuclearforces that operate between fermionsare transmitted by the exchange ofvector or tensor bosons. A significantadvance in the attempt to find asingle description of these fourforces has been made by the unifica-tion of the electromagnetic force andthe weak nuclear force. This elec-troweak gauge theory of Weinberg,Salam, and Glashow (WSG) is de-scribed by the interchange of fourvector bosons—the photon, thecharged W*, and the neutral Z°. Todate, the weak interactions have beenstudied in reactions involving the ex-change of W* and Z° bosons and Z°photon interference. Now, in this ex-periment currently under way atLAMPF, evidence is beginning to ap-pear for Z°- W* interference.

The first publication of results hasnow appeared1 in an article entitled"First Observation and Cross-SectionMeasurement ofve+ e~ —*ve+ e~."At this stage in the experiment theresults agree with the standard(WSG) electroweak theory'.

The LAMPF Line A beam stop is anintense source of 0-to 53-MeVve'sthat are produced predominantlyfrom stopped JI+ decays leading tov^'s, followed by stopped u.+ decaysleading to v/s and v.'s. In the WSGtheory, \ee~ scattering is expected todominate v,,e~and v^e' scattering. Inthis energy range, ve~ scattering(where v without the subscript refersto any of these neutrinos) is confinedwithin a forward kinematic cone of10° for a 20-MeVdetection threshold.Backgrounds to elastic scatteringfrom cosmic rays, from accelerator-associated neutrons, and from otherneutrino reactions are expected to beessentially isotropic. Hence thesignature for ve~scattering is a sharpforward peak in the angular distribu-tion of single electron tracks.

Because a fairly detailed descrip-tion of the detector system was givenin the previous LAMPF Progress Re-port,2 we give here only a brief sum-mary. The large duty factor of LAMPF(6 to 12%) plus the small anticipatedcross section for ve~ scattering resultsin an extremely high cosmic-raybackground relative to the ve~ scat-tering signal, even with the high cur-rent (up to 1 mA) of the LAMPFbeam. To reduce this cosmic-raybackground to an acceptable level,three active and passive shields were

18


used in conjunction with a fine-grained sandwich detector. Figure 1is a cutaway drawing illustrating theprincipal components of the activecosmic ray shield and the sandwichdetector used in the experiment.

The outermost cosmic-ray shieldconsists of steel and concrete with aneffective thickness of more than900 g/cnr This attenuates hadronfluxes by two orders of magnitude.Within this shield is an active anti-coincidence system consisting of s>94multiwire proportional chambers(MWPCs) that cover all inner sur-faces of the massive outer shield.These counters, typically 520 cmlong by 20 cm wide by 5 cm thick, arearranged into four layers in the wallsand roof and a single layer on thefloor. The MWPCs provide a promptveto to reduce online triggers by afactor of 104 and to tag cosmic-raymuons for off-line analysis. Anotherinert shield averaging more than100 g/cm2 of steel and lead is usedinside the MWPCs to attenuate re-sidual cosmic-ray gammas by a factorof 30.

The central detector, which has atotal mass of 15 metric tons arrangedin a 40-layer sandwich structurelocated a mean distance of 900 cmfrom the beam stop, is shielded by630 cm of steel to reduce beam-associated neutrons by more than 15orders of magnitude. The detector isdesigned to identify electrons by themeasurement of dE/dx and to deter-mine electron track direction in spiteof large multiple scattering at theselow energies.

Cosmic-Ray.Veto Tubes

FlashChambers

FIGURE 1, Cutaway view of the neutrino detector. The active cosmic-ray veto system(purple) consists of 594 MWPCs arranged as shown in four layers covering the wallsand roof, with one additional layer on the floor; each counter has eight triangularsections The central detector is a 40-layer sandwich of alternating scintillatorcounters and flash-chamber modules (FCMs). The 160 scintillator counters weigh 9.5tons, and the 208 000 tubes of the FCMs, in alternating horizontal arid verticalorientation as shown, weigh 4.5 tons. In the figure the scintillator counters are paleblue, flash chambers are shown as white layers in the central detector sandwich.

19


Each of the 40 layers in the de-tector is 305 cm high by 305 cm wideand consists of a plane of plastic scin-tillator and a flash-chamber module(FCM). The scintillation plane isconstructed from four 2.6-cm-thickpieces, each 76 cm wide and viewedby a 12.7-cm-diam photomultipliertube, for a total of 160 counters. AnFCM, 1.4 g/cm2 thick, contains 10panels of polypropylene flash tubeswith alternating coordinate readout,5 horizontal and 5 vertical. Eachpanel contains 520 flash tubes ofdimensions 0.5 by 0.6 by 305 cm for atotal of 5200 flash tubes per FCM and208 000 flash tubes in the entire de-tector. The average overall operatingefficiency of the FCM system is 60%per panel and the angular resolutionfor short electron tracks includingmultiple scattering is ±7 ° per projec-tion.

The trigger is defined by a coin-cidence between at least three adja-cent scintillation planes, with energydeposition between 1 and 16 MeVper plane and no veto from theMWPC system. This cosmic-ray vetois defined by MWPC hits in any two ofthe four planes of a wall or roof re-sulting in a veto rate of 7 kHz; a vetoof 20 |o.s is required to reduce triggersby electrons from stopped-muondecays. This gives a 15% system dead-time and results in a residual cosmicray trigger rate of less than 0.1 persecond.

For each trigger, we recorded in-formation from every scintillationcounter, FCM, and MWPC. Also, werecorded information from everyscintillator and MWPC for 32 us

before the trigger to further suppressbackgrounds from stopped-muondecays. Data were taken during theLAMPF beam spill and also during abeam-off gate between spills for acosmic-ray background subtraction.

Our publication was based on dataaccumulated between September1983 and December 1984. The totalexposure was 1.95 A • h of protons(4.4 X 1022) on the beam stop, result-ing in a sample of 98 558 beam-onand 317 740 beam-off events. Thebeam-off to beam-on live-time ratiowas 4.43. Triggers from cosmic-raystopped-muon decays and traversingmuons were also recorded every10 min for calibration and efficiencymonitoring.

After an off-line analysis that(1) tightened cosmic-ray back-ground identification, (2) imposedfiducial volume restrictions, and(3) required an electron signature inthe dE/dx and tracking information,we were left with 1127 beam-on and3864 beam-off events. Correction forthe 4.43 beam-off to beam-on live-time ratio then gave a net number of255 ± 36 beam-associated events.

We show in Fig. 2(a) the histogramof the number of events versus cos 9C

for the beam-on and beam-off events,normalized by live time. Here 9e isthe reconstructed angle of the up-stream part of the recoil electrontrack relative to the direction of theneutrino. Figure 2(b) shows the his-togram of the number of events ver-sus cos Qe for the difference betweenthese beam-on and beam-off sam-ples. In the forward cone, defined ascos 8e > 0.96, a well-defined peakcontains 74.1 ± 13.5 beam-associatedevents. The cos 0,, > 0.96 (0e < 16°)

20


cut is selected with consideration ofve~ kinematics, multiple scattering,and detector angular resolution.Beam associated background in theforward cone is 11 .-i ± 7.0 events.

This result is determined from thenumber of beam-associated events inthe cos 9e interval between 0.84 and0.96, assuming a flat distribution andaccounting for the fraction of ve~events outside the forward cone asdetermined by a Monte Carlo Simulation. The extent of the chosen cos 8,,interval for this background subtrac-tion comes from doubling the for-ward-cone angle-, however, varyingthe extent of the cos 9,, interval inthis subtraction does aot significantlychange this background. The back-ground is due to vp charged-currentinteractions with nuclei and possiblythe capture of energetic neutronsscattered around the 630-cm-thickiron shield at the beam stop. We at-tribute the remaining 62.7 ± 16.7beam-associated events in the for-ward cone to ve~ scattering.

To determine the cross section, theefficiency for detecting ve~ scatteringwas evaluated by use of a Monte Carlosimulation. The simulated eventswere then passed through the data-reduction and data-analysis pro-grams. Cosmic-ray stoppedmuondecay events were also simulated andcompared with observation toprovide confidence in the MonteCarlo analysis. Altogether we as-signed a 9% systematic error to theabsolute detection efficiency.

The absolute neutrino source in-tensity depended on an earlier meas-urement of the number of stopped Jt+

and |a+ decays per incident proton incopper done at the Lawrence

( a )

— BEAM ON

\ BEAM OFF/4 .43

2 0

10

- 1 0

- 2 0

BEAM-ASSOCIATEDBACKGROUND

t •

1.0 0.8 0.6 0.4COS 0 e

0.2 0.0

FIGURE 2 Histograms ol the number ol events versus cos 9e in bins ol 0 02(a) lor beam-on and normalized beam oil events alter the analysis descubed in the

text Here, 9e is the recoil-electron angle relative to the direction ol the incidentneutrino, and

(b) (or the beam-associated events aboveEvents in the forward peak are candidates lor ve~ scattering Beam-associatedbackgrounds in the forward peak are estimated Irom outside the forward peak Onlystatistical errors are shown

21

RESEARCH


TABLE I The Number of Observed ve + e — » v B + e Events Compared withSeveral Possibilities Involving Interference Between Z° and W± ExchangeThe indicated uncertainties lor this measurement are statistical only; lor theexpected number ol events, systematic only

This measurementExpected number ol events

Destructive interference (WSG)No interferenceConstructive interlerence

51 1 + 16 7

53.1± 80108 0± 16 0163.0±25.0

Berkeley Laboratory' 184 in.cyclotron. For the present neutrinoexperiment, a 20cm water degraderwas inserted in front of the beam stopto increase, by 35%, the number ofsuch decays per proton. A simulationof the effect of differing protonenergy and of beam stop compositionresulted in 0.089 ± 0.011 stopped K+

decays per incident 765-MeV proton.Combining in quadrature the 9% un-certainty in absolute detection effi-ciency and the 12% uncertainty inneutrino source intensity results inan overall systematic error of 15%.

The 62,7 ± 16.7 events attributedto v + e~ —* v + e~ contain vê" andvve~, as well as vee~ candidates. Usingthe Monte Carlo simulation, we de-termined the number of expectedvê" and vê" events from measuredcross sections and assigned 4.3 ±1.1and 7.3 ±1.7 events, respectively, tothese two reactions. The remaining51.1 ± 16.7 events are thus assignedto ve 4- e~ —»ve + e~. This number isconsistent with the WSG electroweaktheorv with a vee" cross section of

o(vee~) ={[s.9±3.2 (stat) ±1.5 (syst)]

X10"45cm2/Mev} £v .

The WSG electroweak theorypredicts destructive interference be-tween the Z° and W* vector bosonexchange for vee~ scattering. Weshow in Table I the observed numberof vee~ events and the calculatednumbers assuming destructive inter-ference (WSG), no interference, andconstructive interference. Our resultrules out constructive interference byalmost 4 std dev and begins to ruleout the no-interference case.

Additional data were taken duringthe period from June to December1985. The total number of neutrino-electron scattering events collectedis now more than double the51 events presented above and in ourpaper. A very preliminary analysis ofall the data is shown in Fig. 3, wherethe beam-associated events areplotted against the angle 0e betweenthe recoil electron track and the inci-dent neutrino direction. Improve-ments now being made in our analy-ses are expected to markedly reducethe error, both systematic andstatistical, in the measurement of thevee~ cross section. In an ancillary ex-periment, 866, we will also improvethe systematic error by making amore precise calibration of the neu-trino flux. This will be a new meas-urement of the number of stopped 7t+

and (i+ decays per incident proton.

22

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en

EV

EN

T

o

1BE

R

Z

i c /*\lot)

140

120

100

80

60

40

20

n\j

-10

i i

i

-

" Hi!-

i i

.0 0.8

I I 1 1 I i 1

PRELIMINARY DATA _

ve + e" — » vt + e~

-

-

f :l i j l u , • , , . "

i ' . ' ! ' i i i T i0.6 0.4 0.2 0.0

COS 0 e

FIGURE 3 Beam-associated events from a preliminary analysis for all data taken IromSeptember 1983 to December 1985 As in Fig 2 ,8 e is the recoil-electron anglerelative to the direction ot the incident neutrino The forward peak now contains about1 20 candidate ve~ events

References

1. R. C. Allen et al., Physical Review Letters 55, 2401 (1985).

2. "Progress at LAMPF," Los Alamos National Laboratory report LA-10429PR(April 1985), pp. 51-59.

23

RESEARCH


Cygnus Cosmic-Ray Air-ShowerArray

Los Alamos, Umv ot Maryland. GeorgeMason Llniv , Umv ot New Mexico,Univ oi California at Irvine

Spokesmen: 0. E. Nagle (Los Alamos) and G.Yadh and J. Goodman (Univ. of Maryland)

An array of scintillation countershas been deployed around theExp. 225 detector to search for astrophysical sources of super-high-energy cosmic rays. This search,called the Cygnus project, is a collaborative effort of scientists andtechnicians from Los Alamos, Univer-sity of New Mexico, University of Cal-ifornia at Irvine, and University ofMaryland. It derives its name fromCygnus X-3, a known source of 1012-eV gamma rays located in the direc-tion of the constellation Cygnus.

Cygnus X-3 is thought to be abinary system consisting of a conven-tional star and a compact object, suchas a neutron star or a black hole. It isan intense source of radio, x-ray, andgamma radiations with a 4.8-hperiodicity. There are stochasticphenomena associated with its emis-sions in energy, amplitude, and tim-ing. At this time it is an object of very

active experimental and theoreticalinterest. Several other gamma-raysources appear to exist that havesimilar properties, and studies areunder way at laboratories in both thenorthern and southern hemispheres.The Cygnus project will take high-quality data on gamma sources andmake a significant contribution to theunderstanding of these interestingobjects.

The Cygnus array detects super-high-energy gamma rays (greaterthan 1014 eV) by detecting the extensive cosmic-ray air showers theycreate in the earth's atmosphere.These air showers are thought to bedistinguishable from hadron-induced showers by their electron-to-muon ratio. By triggering theExp. 225 detector (a muon detectorwith a 3-GeV threshold) on a signalfrom the array, which is sensitive toboth low-energy muons and elec-trons, we expect to be able to deter-mine the electron-to-muon ratio inthe shower core.

The array consists of 40 scintilla-tion counters (later to be upgraded to80 counters), located on a grid with10- by 10-m spacing, 60 m in radius,surrounding the Exp. 225 detector.Because of the topography in thebeam stop area, the various counters

24

RESEARCH


are located on roofs, hillsides, andparking lots. Each scintillationcounter is constructed from a disk ofplastic scintillate* 1 nr in area(salvaged from the Volcano Ranchcosmic ray array) that is viewed by a5-cm photomultiplier tube mounted6() cm above the center of the disk.The disk and photomultiplier tubeare enclosed in cone-shapedFiberglas that is lightproof andweatherproof.

The signals from thephotomultiplier tubes are sentthrough coaxial cables to the centraltrigger electronics located in theExp. 225 electronics trailer, where amajority coincidence of scintillationcounters in the array triggers thedata-acquisition electronics and thedetector. The time of the trigger (de-termined by a 60-kHz WWV clock)and the charge and relative timingfrom each of the counters are recorded. Preliminary tests lead us toexpect better than a 2 ns time resolu-tion for each counter. An offlineanalysis will derive the shower frontdirection from the timing and chargeinformation. The number and densityof particles in the shower also will bemeasured by the charge in eachcounter.

The past year's efforts were primar-ily concerned with the physical de-sign and fabrication of the array andits electronics. We plan to devote asubstantial effort to developing theanalysis in the forthcoming year. Wehave a preliminary analysis packageand are examining different fittingstrategies to determine the optimalalgorithim. We expect to begin taking data by the end of February 1986.

25

RESEARCH


EXPERIMENT 657 — EPICS

Plon Inelastic Scattering from theN = 28 Isotones and Neighbors

Univ ot le.sas, Los Alamos, New MexicoState Univ Univ ot Pennsylvania,Biadtord Univ m the United Kingdom,Univ of Minnesota

Spokesman: D. S. Oakley (Univ. ot Texas, Austin)

Experiment 657 is one of severalEPICS experiments that havecentered on the measurements of thedifferences between the neutron andproton multipole matrix elements Mn

and Mp (Refs. 1 and 2). Althoughthere have been some theoretical in-vestigations (Ref. 3), the differencesbetween Mn and Mp observed in(7t,7i') are still not fully understood.

In this experiment we measuredthe cross sections for 7t+ and TI~ scat-tering from 48Ti, 50Ti, 5tV, 52Cr, 54Fe,and 56Fe. Angular distributions weremeasured for all targets between

0lab = 18 and 55 ° at Tn = 180 MeV. Inaddition, 48Ti, 50Ti, MFe, and 56Fe weremeasured simultaneously as striptargets in the incident beam.

The data have been replayed andare now being analyzed. Distorted-wave impulse approximation(DWIA) calculations using collec-tive-model transition densities havebeen used to extract the matrix ele-ments for the 2 | states in several ofthese nuclei, but other models willbe needed to measure the higher-lying states (Fig. 1).

Ic:

10-q

-

I T

0.1--

0.01-(

. . . / • • • * \

D 20

'k ?\ at

yV

40

56Fe(n+,7T

2,+ :

x E

-

_

*»

9 +

i

\

u7 \1 ' 1 *• • 1 " i 1 / • 1

60 80 0 20 # 60(deg) V

80

FiGURE 1 Comparison of collective-model DWIA calculations and data for the 2 |and 2J states ol56Fe

References

1. K. G. Boyer et al., Physical Review C 24, 598 (1981).

2. S.J. Seestrom-Morris, in "Progress at LAMPF," Los Alamos National Labora-tory report LA-10429-PR (April 1985), p. 20.

3. V. R. Brown, A. M. Bernstein, and V. A. Madsen, Physics Letters 164B, 217(1985).

26

RESEARCH


Previous experiments at LAMPFhave shown that angular distributions on 7 = 1 nuclei in the piondouble-charge-exchange (DCX) re-action to residual double-isobaric-analog states (DIASs) do not exhibitminima at the expected diffractiveposition. There have been differentexplanations of these data, which areconsistent for T= 1 nuclei. For 7"= 2DIAS transitions, however, these vari-ous theories predict contradictory re-sults for the angular distributionshapes. Experiments 773 and 906were designed to measure the shapesof angular distributions on two T= 2nuclei, 44Ca (BrookhavenExp. 906)and56Fe (LAMPF Exp. 773), thus dis-tinguishing between correct and in-correct theories. The experimentsran at EPICS between October andDecember 1985 (cycle 44). Replay

and analysis of the data are currentlyunderway. Here we present someonline results from the experiments,along with predictions of the angulardistribution shapes.

A sample spectrum for56Fe(n+,TC~)is shown in Fig. 1. The spectrum isthe sum of all data at 292 MeV and isdominated by the residual DIAS. Theresolution (determined by elasticscattering) is about 700 keV(FWHM), whereas the 4-4Ca(Tt+,rc")resolution was only about 1 MeV. Ineach case the residual DIAS is at anexcitation energy of about 9.5 MeV.At lower energies several other statesare also strongly excited, includingthe ground state, a state just belowthe DIAS (in excitation energy), andone or more states just above theexcitation energy of the DIAS.

70

60

50

30

20

10

o

•

-500 500

LITT

1500

• 1

1 iMjllfli

f i2500 3500

X

\

\. A.4500 5500

EXPERIMENTS 773 and 906 •EPICS

Plon Double-Charge-ExchangeAngular Distributions for T = 2Douhle-lsobarlc -Analog States

Univ. of Texas, Los Alamos, New MexicoState Univ., Univ of Pennsylvania

Spokesmen: G. R. Burleson (New Mexico StateUniv.), H. T. Fortune and R. Gilman (Univ. ofPennsylvania), and P. A. SeidlfUniv. of Texas,Af 'in)

FIGURb 1 Spectrum for double charge exchange (DCX) on 56Fe at 292 MeV

27


10° g—Et i

10-

o 10"

10°

10-

icr

44Ca(it+.n-)44Ti

B f 9 s

IDIAS

t

fi

'A i ,

100 150 200 250 300

T,(MeV)

- G^1-^ J t • : tation functions tor DC.x

;o the res!duai groundstate a"~a ["'-o

A 5 ° excitation function obtainedfor^Ca is shown in Fig. 2. Both thenonanalogground-state (g.s.) transi-tion and the DIAS transition exhibitthe usual characteristics. The g.s.transition is peaked near 140 MeV,which is very similar to s6Fe —»s6Ni(g.s.) but about 20 MeV lower than inlighter nuclei. The DIAS transitioncross section increases mono-tonicilly between ~ 160 and~300 Mev, as seen for all DIAS tran-sitions.

Angular distributions are shown inFig. 3. (A partial angular distributionwas also obtained for the 56Fe DIAS at164 MeV and for correspondingground-state transitions.) The curvesrepresent predictions of three dif-ferent models. The curve with a for-ward minimum (dot-dashed)predicts no shape difference be-tween DIAS transitions on T= 1 andT= 2 nuclei. The middle curve(dashed) is a standard lowest-orderoptical-model calculation, and thecurve with the minimum movedoutward (solid) is a prediction of thesecond-order optical-potential the-ory of Johnson and Siciliano. Thecross sections displayed result from

summing area gates (zero back-ground has been assumed). Thealmost constant results are mostsimilar to the second-order predic-tion. However, given the 4tTi and 5<iNispectra, estimates of the backgroundwill have to be made to better esti-mate the uncertainty in the angulardistribution shape.

56Fe(7i+,jT)56Ni(DIAS)!;

292 MeV

Ca(7t+,7t-)4'1Ti(DIAS):

10"3!0 10 20 30 40 50 60

e

FIGURE 3 Comparison of the angular

distribution at 292 MeV lor56Fe(7i+,7t")56Ni (DIAS) with prediction ol

the PIESDEX lowest-order calculation,

and of the angular distribution at164 MeV lor 44Ca(jt+,7t~)44Ti (DIAS)with predictions of various model0.The curves are described in the text.

28


The amount of data available forinvestigation of the mass dependence of pion double charge exchange (DCX) has increased severalfold over the past few years. Beforeany experimental evidence becameavailable, Johnson' derived the massdependence of sequential singlecharge exchange leading to double-isobaric analog states (DIASs) as

do(qx=0) cc (,V-Z)

dii.

Several subsequent articles havemade graphical comparisons of data(tvpically at 0lab = S°) with the aboveexpression.2 6 No similar expressionhas been derived for nonanalogg.s. —» g.s. (ground-state) DCX, butthe mass dependence has beenclaimed to be A~A/i in some articles,again based on graphical com-parisons. Here, we report results of anumerical comparison of data withsome possible DCX expressions.

For both nonanalog and DIASDCX. we have simultaneously fittedthe mass dependence of 5,°b crosssections at several incident beamenergies. We have used three dif-

ferent mass dependence functions:1. (TV- Z)(N- Z-\)A~\

2. A~x,and

3. MTV- l)A-\The function ( W - Z H / V - Z - 1)A~X,with -v ~ 10/3, represents the ex-pected form of the DIAS mass de-pendence. The function A~x, with-v ~ 4/3, has been used previously2'7

to describe nonanalog DCX. TheMJV-1 )A~X mass dependence, with.\- ~ 10/3, represents a collectiveenhancement in the cross sectionsover the expected A~Wi because thecross section is proportional to thetotal number of neutron pairs ratherthan the number of excess neutronpairs to which we expect DIAS DCXto be sensitive.

The results of these fits are givenin Table I. For the nonanalogdata, the large x2 for the(TV- Z){N— Z- \)A'Xmass de-pendence indicates that it is in-appropriate. This is to be expected,as there are many nonzero cross sec-tions for N = Z nuclei. TheN(N— l)A~x and/T* formulas resultin comparable fits. For the large frac-tion of the nonanalog data that hasbeen measured on N= Z targets,these two dependences are indis-tinguishable (given the experimentaluncertainties). A reduced y? value of2.3 for the A~xdependence, however.

EXPERIMENTS 777, 780, and826 — EPICS

Mass Dependence of Plon DoubleCharge Exchange

Univ. of Texas, Los Alamos, New MexicoSlate Univ., Univ of Pennsylvania

Spokesmen: G. R. Burleson (New Mexico StateUniv.), H. T. Fortune and R. Gilman (Univ. olPennsylvania), C. L Morris (Los Alamos), andP. A. Seidl (Univ. of Texas, Austin)

T"BL.F S'mijitaneous Fits ol the 4 Dependence at all Energies

ype Form Exponent

Nonana'og(N— Z ) ( N —(N){N - 1 )A~

M

(N- Z ) ( / V -I— 1)4"

Z- 1)4"

Z- 1)4-

2152

737

30948

481503

— 1- 3- 3 .

- 1- 3- 3

35 ±025 ±051+0

79 ± 029 ±072 ±0

061306

0704.07

29

RESEARCH


may indicate that this is an inade-quate representation of the data. Wenote that one effect that will increasethe x2 is the decrease of the peakenergy of the excitation functionwith increasing target mass. Belowthe peak energy, this will result inheavier-mass nuclei being closer tothe peak and will slow the mass de-pendence. Above the peak energy,the mass dependence will increase.We return to this point below.

In Table II we present fits to thenonanalog data, done independentlyat each energy with the A~x function,and fits of two energy-independentparameters. The quantity g is a mag-nitude parameter for fits to thenonanalog excitation-functionshapes (all are peaked near 160 MeVand are represented with Breit-Wig-ner functions). The quantity o( To) isthe maximum cross section of thenonanalog excitation functions inde-pendent of energy. The energy de-pendence is consistent with the de-scription given above; a more quan-titative comparison is made below.Given the energy-dependent results,

the fits to the energy-independentquantities CT( TO) and g, and the simul-taneous fit to all energies, we con-clude that, on average, an A depend-ence of A"*n represents nonanalogDCXwell.

Fits to DIAS DCX with the variousmass dependences are also shown inTable I. The only possibly adequaterepresentation of the DIAS mass de-pendence is the expected mass de-pendence formula, for which the ex-ponent agrees with the expectedvalue of—10/3. Table III presents fitswith the expected mass dependenceformula at each energy. At everyenergy the best-fit exponent is con-sistent with —10/3 within errors. Themajor energy dependence is thelarger %2 at the lower energies thatresults from the greater scattering inthe data.

In Fig. 1 we present the energydependence of the fitted exponentsof Tables II and III. The DIAS expo-nents are essentially independent ofenergy, despite a variety of excita-tionfunction behaviors. We know ofno simple explanations of the fact

TABLE

7*

120

130

140

164

180

210

a(7"0)

9aThe da/

II Results of Nonanalog A "Fits at Each Energy,3

X2

2 16

0 0 1

0 8 7

1.38

3.15

1.01

0.30

1.29

dn[A(nb/

1

93(±12)

54(±28)

133(±16)

118(±8)

50(±5)

53(±9)

142(±29)

Exponent

- 0 77(±O 16)

-0.40(±0 20)

-O97(±O 15)

-1.42(±0.09)

- 1 81(±0.13)

-1,28(±0 20)

- 1 11 (+0 22)

O.O25(±O.OO5) -1.47(±O.2O)

sr)} = l'A/A0r*.with^o = 4 0

Constrained A~*/3 Fit

X2

3,58

3 58

1,37

1 36

3.98

0.91

1 19

0 3 8

f

60(±6)59(±12)

105(±9)124(±6)

56(±5)

51(±4)

117(±12)

0028(±0.003)

30

RESEARCH


that at lower energies there is nochange to the DIAS mass depend-ence. Nuclear-structure effects mightbe expected to only add scattering tothe data. The p2 terms, six-quark bags,and doubleisobaric nonanalog-transition (DINT) mechanisms that havebeen proposed as important to understanding resonance-energy DIASDCX, however, might be expected tomodify the A dependence.

The nonanalog exponents, in contrast, have a striking energy depend-ence, even though the whole data setwas simultaneously fitted by an exponent that was about —4/3- We haveestimated the effects of the variationin nonanalog excitation-functionshapes with mass on the A dependence. The result (with error band) isshown as a set of dashed lines inFig. 1. The variation with energy issimilar to that of the fits to the dataand agrees with the description givenabove. This comparison indicates

FIGURE 1 Variation with energy of the best-fit exponents for the DIAS and nonanalogmass dependences The DIAS exponents are compared with the expected value of— 10/3 (solid line) The nonanalog exponents are compared with a prediction (seetext) based on the Breit-Wigner excitation-function fits The dashed lines show theprediction and error bands, and the dotted line is at—4/3

TABLE III Results o( D lAS( /V- Z)(N- Z- 1 )A~* Fits at Each Energy a

T* x2 ' Exponent

100

120

140

164

180

211

230/5

260

292

79

64

6 7

4 0

34

003

28

1 8

2 1

12(±4)

24(±5)

16(±4)

15(±2)

18(±1)

29(±4)

39(±4)

64(±13)

68(±3)

-332(±O,32)- 3 23(±0 21)

- 3 31 (±0 23)

- 3 43(±0 14)

—3.47(±0.11)

-3,23(±0 20)

- 3 37(±O 16)

-3,00(±0 26)

-3.24(±0.05)a T h e d o / c < n [ 4 ( n b / s r ) ] = I { N - Z ) [ N - Z- 1 ) I A / A o r * . w i t h A 0 = 4 2

31


that much of the energy variation ofthe exponents arises from the factthat the nonanalog energy dependence is slightly different for dif-ferent nuclei.

In summary, the mass depend-ences of both analog and nonanalogDCX may be approximated by re-latively simple formulas,

(TV- Z)(N- Z- l)/r'0/3forDIASDCX and A~m for nonanalog DCX,that are applicable over a wide rangeof masses. In both cases the quality ofthe agreement between data and for-mula varies with energy. For DIASDCX the mass-dependence exponentis independent of energy, but thequality of the agreement is muchworse at lower energies. Fornonanalog DCX the quality of theagreement is fairly good at eachenergy, but the exponent varies withenergy.

References

1. M.B.Johnson, Physical Review C 22,192 (1980).

2. C. L. Morris et al., Physical Review C 25, 3218 (1982).

3. S. J. Greene et al., Physical Review C 25,927 (1982).

4. P. A. Seidlet al., Physical Review Letters 50,1106 (1983).

5. K. K. Seth et al., Physics Letters 155B, 339 (1985).

6. P. A. Seidlet al., Physical Rei'ieiv C 30, 973 (1984).

7. L. C. Bland et al., Physics Letters 128B, 157 (1983).

32

RESEARCH


Measurement ot neutron andproton transition amplitudes in "2Neusing 7i~ and 7t+ inelastic scatteringallows meaningful comparison withsophisticated shell-model calcula-tions in the lightest T= 1 nucleus notplagued by low-lying "intruder"states.

Experiment 800 was run during cy-cle 43 using the EPICS cooled-gastarget with the rare-gas-handlingequipment. Spectra were obtainedfor22Ne(Ti,7t') at an incident pionenergy of 180 MeV in the angularrange from 14 to 90 °.

Figure 1 shows the spectra ob-tained at 0,ab = 70°. The data fromthis experiment have been replayedand extraction of the angular dis-tributions from the spectra is in pro-gress. Figure 2 shows the angular distributions for the first 2+ and 3" statesin"Ne.


Inelastic Plon Scattering from uNe

Los Alamos, Michigan State Univ , Univ.ot Minnesota, Ui liv. ol Pennsylvania,Univ of Texas

Spokesmen: H. T. Fortune (Univ. ol Pennsylvania)and C. F. Moore (Univ. ol Texas, Austin)

Io

0.1

0.0

i r \ • T ^ r r i ^ i ^ i

„ c^ X O 7Y

x 5

-—^L^j^jy\,^^0.04 *>

0.00

-0.04

I

a 0.1

0.0

x 571

'.,. L0 4 8 12 16

Excitation Energy (MeV)

FIGURE 1 Then+and)x spectra at 0iab = 70° along with the quantity (o_ — o+)

•§.

c:

CO

10

1

0.1

0.01

0.001

0.0001

1 1 1 1 . 1 . 1 .

1.275-MeV

- • SB

M

1

T M g - ,

r

I 5.910-MeVr X 1/10

. 1 . 1 . 1 . 1

3 20 40

t ' ( • I '

2f 7T

TV

* * 8x« *m

X

'"sX(D

3T X « «

f l

. i . i . i .

60

(deg)

1 ' 1 ' :

+ :X

__ -i

o i'._:

I

• l

? l :

a,

80

FIGURE 2 The cross sections (c m ) lorrt') to the first 2 + and 3 " states

33

RESEARCH


EXPERIMENT 833U — EPICS

Large-Angle Excitation Functionsfor Elastic Scattering of R- from "Cand"0

Me-A Me * ico>' '.tale Univ , Univ ot Texas,

LOS Alanx-:., Mmv oi Pennsylvania,

'jni'v ol rvVvieouKi

Spokesman: G. R Burleson (New Mexico StateUniv.)

Although a great deal has been'earned about the pion nucleus inter-action from measurements that haveprincipally involved scattering overthe forward hemisphere, very little isknown about scattering at anglesgreater than ~ 120 ".The only published large angle data, for nucleiwith A > 4 and pion energies in therange of the A( 1232) resonance, inelude angular distributions for JT* on

1213CatlOOMeV(Ref. D . ^ o n 12Cat162 MeV (Ref. 2),Tt*on 16O at114 MeV(Refs. 3and4),and7t+on16O at 163 and 244 MeV (Ref. 4).There is much interest in studyingelastic scattering in this angular re-gion because the predictions of vari-ous theoretical models, which arefairly successful in describing the for-ward-angle data, diverge considerably beyond 100°.

1C

t

101

10°

10"1

10"2

io-3

10°

10"1

10"2

=•

-

=•

-

80

1 1 ' 1 ' 1

5 s

\ *

X0

\ »

\ \

i I , i i I

110 140 170

Energy (

1 i •

TTTT~

s

1

200

MeV)

nm

i TT+ =J TT" _

X

PIRK+ Solid IDashed \

z

1 1

230 260

FIGURE 1 Measured excitation lunctions (at 1 75°) lor n+(crosses) and ;t (opencircles) on 12C and 16O The lines are optical-model (PIRK) calculations

34

RESEARCH


Recently, measurements showinglarge differences between 7t+ and ri~scattering from l6O at 114 NieV forangles near 180° were reported.3 Calculations using pion-nucleus scatter-ing models that include the Coulombinteraction and second-order termswere unable to reproduce the dataover the full angular region. We feelthat it is important to study thesedifferences further, because they mayhelp determine certain features ofthe nuclear amplitude, as has beenfound at small angles.5

We also feel that measurements ofpion-scattering cross sections at largeangles will help in understandingsecond-order effects in the pion-nucleus interaction. For thesereasons we have made an experimen-tal determination of the rc+ and 7t~scattering differences near 180°, aswell as a study of the generalbehavior of large-angle scatteringwith energy. Here, we report the firstmeasurements of large-angle excita-tion functions for n+ and 7i~ scatteringon nuclei with A > 4. The data weremeasured using 12C and l6O targets at175° for ;t+energies between 100 and230 MeV and TC~ energies between100 and 200 MeV.

The experiment6 was performed atEPICS. The measurements were car-ried out with the back-angle EPICSsetup, which is described in Ref. 7.Absolute normalizations were ac-complished through the comparisonof i^p yields, measured with a CH2

target ofareal density 211 mg/cm2,with the u^p cross sections calculatedusing the phase shifts from Ref. 8.The normalization uncertainty was±10%.

The data are presented in Figs. 1and 2. All the excitation functionsdecrease with increasing incidentenergy and exhibit a broad structurewith a minimum between 100 and150 MeV. The 7t+ and iC excitationfunctions on 12C are similar in shapeand position of the minima and aredifferent by less than 30% in magni-tude. For 16O the 7i+ and K~ shapes arealso similar, but the 7t~ minimum

101

10°

10"

^ 10"

1 10"

•° io°

10"

10"

10"8

-

-

=

i 11

• ••

•! i

ii

IIIIII I II

IIIIII i

-

0

1

"c

16Q

, 1

no

i • i

" " • \

\ J

l '

imn

iiin

il

i i

1 TT _

z

-

Ernst et al. *

TT+ Solid Iir Dashed ;

i

i ,

140 170 200

Energy ( MeV)

z

1 ,

230 260

FIGURE 2 Data as in Fig 1, but with the calculations of Ernst et al (see text)

35


occurs about 10 MeV lower than then+ minimum. The differences in magnitude between the 7t+ and n~ data arelargest near ~ 120 MeV and aregreater for l6O than for 12C. For 1(1Othere is a suggestion of a secondminimum near 180 MeV, but for UCthe data appear to vary smoothly inthis region.

To investigate the origin of thestructure seen in the excitation func-tions, we have performed various op-tical-model calculations. One ofthese used the elastic-scattering codePIRK,9 as modified by Cottingame andHoltkamp.10 This code uses a zero-range coordinate-space model with amodern version of the Kisslinger op-tical potential." The results of thecalculations are displayed in Fig. I.Although these calculationsreproduce some features of the ex-citation functions, the calculatedcross sections are generally smallerthan those in the data by at least afactor of 2 at lower energies and by anorder of magnitude at higherenergies. The minima seen in thedata are reproduced by PIRK within15 MeV. At higher energies, however,the calculations indicate similarstructures that are not observed in thedata, except possibly for lf'O at a reduced level.

We have also used the field-theo-retical momentum-space model ofErnst et al.12 Features of this ap-proach include an exact treatment ofrelativistic kinematics, the incorpora-tion of the finite range of the pionnucleon amplitude, and the exactevaluation of the Fermi averaging in-tegral. This last feature allows themodel to incorporate the formation,propagation, and decay of theA( 1232) resonance. The results areshown in Fig. 2. The qualitative fea-tures of the measured excitationfunctions are again reproduced witha noticeable improvement for UC.However, the magnitudes of thepredicted cross sections at higherenergies are still too small.

In summary, the qualitative agree-ment of the optical-model calcula-tions with the data is encouraging.However, the question of the originof the generally larger absolute magnitude of the data is still unresolved,as is the disappearance of thepredicted minima at the higherenergies. As was found in an earlierstudy,3 higher-order terms in the op-tical potential or additional effectsnot included in the models may benecessary to reproduce the cross sec-tions at large angles. (Calculationsalong these lines are in progress.)Because the n+ and n~ excitationfunctions are not reproduced in de-tail, a better understanding ofCoulomb distortions and of the inter-ference of Coulomb and nuclearamplitudes is needed. In this respect,it is clear that large-angle pion-nucleus scattering affords a uniqueopportunity to explore further thepion-nucleus interaction.

36

RESEARCH


References

1. I.E. Antonuk et al., Nuclear Physics A420, 435 ( 1984).

2. B. Chablo/.et al., Physics Letters SIB, 143 ( 1979).

3. K. S. Dhuga et al., Physical Review C 32, 2208 ( 1985).

-1. V. Bason et al.. Physics Letters 118B, 319 ( 1982).

5. J. F. Germond and C. Wilkin, Annals of Physics (New York) 121, 243(1978).

6. H. A. Thiessen and S. Sobottka, Los Alamos National Laboratory reportLA-n3-i-MS(1970).

7. \V. B. Cottingame et al., Los Alamos National Laboratory report LA 10201 •MS (1984); and G. R. Bnrleson et al., "A Large-Angle Pion-NucleusScattering Facility for EPICS at LAMPF" (submitted to Nuclear Instru-ments & Methods).

8. G. Rowe, M. Salomon, and R. H. Landau, Physical Review C 18, S84

9. R. A. FJsenstein and G. Miller, Computer Physics Communication 8, 130( 1974).

10. W. B.Cottingameand D. B. Holtkamp, Physical Review Letters 45, 1828(1980).

11. L. S. Kisslinger, Physical Review 98,761 (1955).

12. L). L.Weiss and D.J. Ernst, Physical Review C 26, 605 (1982); and M. B.Johnson and D.J. Ernst, Physical Review C 27,709 (1983).

37



Energy Dependence of PlonScattering to the Giant ResonanceRegion of l l lPb

Univ ol Minnesota, Univ ot Pennsylvania,Los Alamos, Univ ot Texas, Univ olColorado. Univ ol Orsay

Spokesperson: Susan Seestrom-Morris (Univ. otMinnesota)

Experiment 836 ran at EPICS inJuly 1985. The objective was tomeasure the energy dependence ofthe ratio Mn /Mp extracted for thegiant quadrupole resonance (GQR)in 208Pb as a function of incident pionenergy. We hope that these measure-ments will be helpful in understand-ing the large ratios previously ob-served at 7J, = 162 MeV in Exp. 672.

Cross sections were measured forK+ and 7t~ scattering to the GQR at7; = 120,162,200,250, and 300 MeV.The 162-MeV data were measured foran overlap with the existing 162-MeVdata as well as to add a new 7t+ pointat 162 MeV. At 120 MeV, JI+ data weretaken at 23,26, and 29°, and n~ datawere taken at 19 and 24 °. At 200 MeV,the Jt+point is at 18° and then" pointis at 16°. At 250 MeV, the 7t+data were

taken at 12,15, and 17°, and the ndata were taken at 12,14, and 16°,The 3OO-MeV7t+point was at 13°; the7t~ point was at 12°. In the cases forwhich only a single angle wasmeasured, this angle was chosen tobe at the same momentum transfer asthe peak in the 162-MeV angular dis-tributions. The replay and normaliza-tion of the data are complete andpeak fitting of the spectra is in pro-gress.

The results of the preliminary peakfitting indicate some energy de-pendence to the ratio of 7t~ to 7t+ crosssections. At 120 and 162 MeV thisratio is about 3, whereas from 200 to300 MeV it is <2. The preliminaryangular distributions have beenanalyzed by comparing them withdistorted-wave impulse approxima-tion (DWIA) calculations usingTassie-model transition densities toextract values for the neutron andproton matrix elements Mn and Mp.These are plotted as a function of

38

RESEARCH


pion energy in Fig. 1. There is someevidence for an energy dependenceto the extracted Mn. The Mp — M»seems to increase with increasingpion energy, whereas Mn seems todecrease. However, because of thelarge uncertainties in these quan-tities, a straight line would also give areasonable description of the data.Using the average values of Ma andMp gives a ratio of Mn/Mp — 2.8,which is smaller than that de-termined at 162 MeV, Mn/Mn - 3.8.

We are investigating the effect ofthe shapes of the transition densitieson bodi the values and energy de-pendence of Mn and Mp. So far thetransition densities studied are lim-ited to Tassie and collective models,with variation in geometry. No signif-icant differences were found be-tween results obtained using Tassiemodel transitions densities and thoseobtained using collective-modeltransition densities. A test wasperformed by varying the radius pa-rameter of the distribution, whosederivative is used to calculate the

Tassie model transition density. Thisessentially moves the peak of thetransition density without changingthe shape. If this parameter ischanged so that there is a 1 -fm dif-ference between its value for neu-trons and that for protons, the extracted value of Mn/Mpu\n be reduced from 3.8 to 1.54 (N/Z). This isan unreasonably large difference be-tween the neutron and proton distributions; also, it does not changethe energy dependence of the ex-tracted Mn and Mp. However, it is stillpossible that, by use of transitiondensities for which the neutron andproton shapes are different, a value ofMn /Mp nearer the theoretically expected value of N/Z could be ob-tained. Such shape differences couldresult from random-phase-approx-imation (RPA) calculations that seemto predict larger tails for the neutrontransition densities than for theproton transition densities.

208Pb(ji,n')20BPbGQR

Tassie Model (cD - cn = 6.51)

<Mn> - 1 0 5 e f m 2

<MP> - 38 elm2

<Mn>/<Mq> - 2.8

100 150 200 250 300 350

Pion Energy (MeV)

FIGURE 1. Preliminary values of Mn andMD for the GQR in 20BPb extracted usingTassie-model transition densities

39

RESEARCH



New Test of Superratlo by n+ ElasticScattering on JH and 3He

UCLA, George Washington UnivAbilene Christian Univ

Spokesman: B. M. K. Nefkens (UCLA)

Experiment 905 is a new measurement of n+ and 7t~ scattering on 3Hand 3He to investigate, simultane-ously, elastic and inelastic scatteringslightly above nuclear breakup. Theexperiment was done at EPICS atthree different energies (142,180,and 220 MeV) and at five differentangles (40,60,80,90, and 110°). Theobjectives of the experiment are

1. to probe the nature and extentof charge symmetry breaking asmanifested in the deviationfrom unity of the superratio,

do(K+ 3H) "I / [ " da(n+ 3He)"|

*J(B"JHe)J/ L dotor JH) JL«*J(B

(1)

Our previous result1 at7; = 180 MeV and Qn = 60 ° forelastic scattering implied thatthere is a definite intrinsiccharge-symmetry violation inthe strong interaction; and

2. to compare the 3H,3He, and 4Heform factors. In the vicinity of70° a comparison of da(n+ 3H)with da(r(~ 3He) elastic scattering is a comparison of the un-paired nucleon of 3H and 3He-,similarly, outside 70° indaiiC 3H) and da(.K+ 3He) themass form factors of the pairednucleons are compared.

Finally, coupling the new resultswith existing da(n+ ''He) provides aninteresting comparison of the formfactors and radii of 3He and 4He.

It has been argued by Weinbergand others2 4 that quantum chromo-dynamics (QCD) implies a small in-trinsic violation of charge symmetry.Unfortunately, this violation has thesame magnitude as that caused by theeverywhere-present electromagneticinteraction, which makes it difficultto pin down the intrinsic violation ofcharge symmetry in any reaction,

A novel test for the validity ofcharge-symmetry violation can bemade by measuring the supeiratio,which we have defined [see Eq. (1)]as the ratio of ratios of two pairs ofcharge-conjugate reactions. If thecharge symmetry is valid, R= 1 ateach angle and at all energies aftercorrections have been made for elec-tromagnetic effects. Looking at thecharge-symmetry violation using thesuperratio has several distinct advan-tages.

1. Electromagnetic corrections aresmall (we estimate, less than afew per cent).

2. The A resonance plays a majorrole in pion scattering on lightnuclei, specifically the A~ in theJT 3H scattering and A4""1" init+ 3He. Quark-model calcula-tions58 give a mass difference ofabout 5 MeV between A"1"1" andA" leading to R= 1.

3. Pion scattering covers a largerange of four-momentum trans-fers t, up to 10 fm"2 in our case.This permits a measurement ofpossible differences in the 3Heand 3H matter and spin form factors over a wide range of /.

40

RESEARCH


4. From an experimental point ofview the superratio method ismore elegant, mainly because ameasurement of R is completelyindependent of the absolutebeam calibration as well as theefficiency and acceptance of thepion detector.

Our previous results for the super-ratio1 R at pion energies of 142 and180 MeV deviate very much fromunity. Among the suggested explanations for the observed deviations of Rfrom unity are

1. do(K+p) ¥= do(iCn), which isexpected if A"1"1" and A~ have dif-ferent masses;

2. F(3H) =£F(3He), where F is theform factor. Such a differencecould in turn be the conse-quence of different" couplingconstants, g(pp7t°) ¥= g(nnn°);

3. a possible charge-symmetry-violating, three-body interac-tion9-, and

4. all of the above.Important insight into the reaction

mechanism for the pion-nucleus scat-tering comes from a comparison ofthe ratios p, = rfa(7i+3H)/rfa(jc+3He)and p, = daiiC 3He Wa(jc~ 3H) orclastic and inelastic scattering. Theseratios have no special values exceptthat charge symmetry requires thatPi = P2' They are easily measuredwithout having to worry aboutabsolute beam calibration. Our previ-ous result shows striking dissimilaritybetween elastic and inelastic scatter-ing. This difference is due mainly tothe suppression of the spin-flip con-

tribution in the elastic channel. Thus,measurement of the ratios p, andp2

for the elastic channel together withthe inelastic channel provides apowerful, yet simple, measure of thespin-flip contribution to nT 3H scat-tering. Also, the comparison of thesuperratio for elastic scattering withthat for inelastic scattering is a novelprobe of the contribution of the elec-tromagnetic interaction.

To differentiate among the abovepossibilities requires knowledge of Rat various pion energies, Tn =* 140 to290 MeV, covering the A resonanceand spanning a wide range of anglesfrom 30 to 120 °. The variouspossibilities each have their ownsignature. If R at 100° changes signfor high momentum, it is suggestiveof explanation 1; if R depends onlyon t, it must be explanation 2.

The experiment was performed atEPICS from June 17 to July 6,1985.EPICS has the appropriatecharacteristics for this experiment,namely a large pion flux(~ 10a pions/s), good energy resolu-tion, and a large acceptance for si-multaneous measurements of elasticand inelastic scattering. This enabledus to measure the superratio for theelastic and inelastic scattering with aminimum relative error.

We used five targets having a cylin-drical shape 12.7 cm in diameter and22.9 cm high, made of specialaluminum (aluminum alloy 2024-T3511), which has a small diffusioncoefficient for tritium and a high

41


tensile strength (65 000 psi mini-mum). The walls of the cylinderswere 1.85 mm thick. The cylinderswere tested thoroughly for gas leaksand strength by pressurizing up to700 psi with helium before beingfilled with the gases. The gases usedwere T2, H2,

3He, and D2.The fifth cylinder was evacuated to

make the empty target. The averagepressure in the cylinders was 450 psi.The pressure and weight of eachcylinder were accurately measuredbefore and after the experiment. Thepurity of each gas was determinedspectroscopically. Because of thehigh radioactivity involved, a special

tritium enclosure and vent/recapturesystem was used. The target ladder atEPICS was slightly modified to ac-commodate the new target system.We used an incident momentum ac-ceptance of 2% for all the runs. Theenergies of the incident pions (Jt+

andTt") used were 142,180, and220 MeV at lab angles of 40,60,80,90,and 110°. At each angle, wemeasured successively the n+ yieldfrom the tritium, 3He, and hydrogentargets with the spectrometer tunedfor pion-tritium kinematics, yielding

Pl =Y(n+ 3H -» 7t+ 3H)

rc+ 3 He — 7t+ 3He)

i . o -

12-

1.1-

0.9-

0.8-

0.7-

I

i

T, = 142 Mrif

l 1 • i

i i i

20 40 60 80 100

SCATTERING ANGLE (DEG)120

FIGURE!, Preliminary results for the superratioR at Tn = 142 MeV.

142


The background was measured usingthe hydrogen as well as the emptytarget. The measurement of p, wasfollowed by data collection on thehydrogen target, deuterium target,and empty target, with the spec-trometer tuned to the JI-D kinematics.A comparison of these data with theknown hydrogen and deuteriumcross section will give the normaliza-tion that will be used to calculate theabsolute cross section. The same sequence with the same kinematics wasrepeated for the iC beam to get p2,

Now the superratio is obtained asR—Pi • p2. Because at large anglesthe cross sections are small, we werenot able in the time allocated for theexperiment to collect enoughstatistics for the 120° angle. Also, wedid not look for the dip around9^= 70° very carefully. We plan an-other experiment in the near futurefor this purpose.

The analysis of the data is proceeding. Preliminary results for the super-ratio R at TK = 142 MeV are shown inFig. 1.

Hit" Hie — jT'He)

References

1. B. M. K. Nefkens, W.J. Brisco, A. D. Eichon, D. H. Fitzgerald, J. A. Holt, A.A. Mokhtari, J. A. Wightman, M. E. Sadler, R. Boudrie, and C. Morris,Physical Review Letters 52,735 (1984).

2. S. Weinberg, in "A Festschrift for I. Rabi," Transactions of the New YorkAcademy of Sciences 1,185 (1977).

3. P. Langackerand H. Pagels, Physical Review D19,2070 (1979).

4. D. Gross, S. Treiman, and F. Wilczek, Physical Review D19,2188 (1979).

5. H. R. Rubenstein, Physical Review Letters 17,41 (1966).

6. R. P. Bickerstaff and A. W. Thomas, Physical Review D 25,1869 (1982); andN. G. Deshpandeetal., Physical Review D15,1885 (1977).

7. K. F. Liu and C. W. Wong, Physical Review D 17', 920 (1978); and N. Isgur,Physical Review D 21,779 (1980).

8 F. Myhrerand H. Pilkuhn, ZeitschriftfuerPhysik 29,675 (1984).

9. j . Friar etal., Comments on Nuclear and Particle Physicr, 11,51 (1983).

43

RESEARCH


EXPERIMENT 392 — HRS

Measurement of the WolfenstelnParameters for p + p and p + nScattering at 500 and 800 MeV

Univ o' Texas at Austin, Rutgers Univ

L os Alamos

Spokesman: G. W. Hoftmann (Univ ot Texas,Austin)

The protonnucleon scatteringamplitudes are necessary first-orderingredients for microscopic descrip-tions of proton-nucleus scatteringthat use the impulse approximation(IA) (both the nonrelativistic and rel-ativistic approaches). Lack of suffi-cient data forpnucleon scatteringfrom 500 to 800 MeV, particularly atsmall momentum transfers, has in thepast led to ambiguous or poorly de-termined scattering amplitudes. Theobjective of Exp. 392 is to provideadditional p-nucleon scattering dataat 500 and 800 MeV that will furtherconstrain the scattering amplitudes atsmall-to-medium momentum trans-fers.

The experiment is divided into twophases at each energy: (1) freeproton-proton {pp) measurementsusing a liquid-hydrogen target and(2) quasi-elastic proton-proton andproton-neutron (pn) measurementsusing a liquid-deuterium target. Inboth phases, incident beams ofprotons, polarized in the h(up, down),S (left, right), and C(parallel, antiparallel-to-the-beammomentum) direction, are scatteredfrom the target.

The high-energy scattered protonsare detected by the HRS and arerescattered at the HRS focal-plane-polarimeter (FPP) carbon analyzer inorder to determine the spin compo-nents of the outgoing protons (trans-verse, vertical and transverse,horizontal). Because of the pre-cession of the spin components thatare not parallel to the HRS magneticfields, the spin components de-

termined by the FPP are actually mix-tures of the orthogonal set of spincomponents at the target. This pre-cession facilitates measurements ofthe outgoing spin components thatlie along the momentum of the parti-cles at the target, and it is also thereason that certain spin componentscannot be determined over certainangular ranges (at some angles thesecomponents precess to longitudinalor nearly longitudinal spins at thefocal plane). The polarizations de-termined at the focal plane, there-fore, must be separated into the ap-propriate polarization components atthe target before the triple-scatteringparameters can be determined.

In the quasi-eleastic phase of theexperiment, a second arm, the recoil-particle-detection system, is used todistinguish betweenpp andptt scat-terings. By requiring either a recoilproton or a recoil neutron in coin-cidence with the event detected bythe HRS, both quasi-elastic pp andpn triple-scattering parameters maybe measured. A comparison betweenelastic and quasi-elastic pp data isalso made to indicate the validity ofusing quasi-elastic pn (deuteriumtarget) results to determine free-scat-tering amplitudes.

Both the 500- and 800-MeV phasesof Exp. 392 are complete. The 800-MeV results are published in Refs. 1and 2, and the 500-MeV data are nowin final form. These data are com-pared with recent phase-shift predic-tions of Arndt* in Fig. Ka)-(e) forpp data and in Fig. 2(a)-(e) for pndata. An overall normalization

•Reference 3. and information on the WI84 solutionprovided by Richard A Arndt, Virginia PolytechnicInstitute and Slats University, 1984

44


uncertainty of ±0.01 (±0.02 for theparameters DLS and Du , has notbeen included in the error bars butshould be applied to all data. As seenin the figures, the 500-MeV scatteringamplitudes appear to be reasonablywell determined. The agreement be-tween data and phase-shift solution

also provides further support for theequivalence of free nucleon-nucleonand quasi-elastic (deuterium)nucleon-nucleon measurements atthese bombarding energies and inthe range of momentum transferspanned by Exp. 392.

,1 R

0 4

(b)

'0 20 30 40 50 60

0 10 20 30 40 50 60 0 10 20 30 40 50 60

9cm (deg)

:> 3

0 6

"1 .!

0 2

0

•Vi

(e)

•

0 10 20 30 40 50 60

9cm (deg)

FIGURE 1 The 500-MeV elastic and quasi-elastic pp triple-scattering parameters(a) DNN, (b) Dss. (c) DSL, (d) DLS, and (e) DLL. The solid curves are phase-shiftpredictions (solution WI84) The free pp data are indicated by solid dots, and thequasi-elastic data are indicated by crosses

45


1 4

l 2

• 1.0

0 8

06

04

(a)

Q

1 0

08

,0.6

' 0 4

0.2

0

(b)

0 10 20 30 40 50 60 0 10 20 30 40 50 60

(d)

10 20 30 40 50 60

1.0

0.8*

^ 0 6

10 20 30 40 50 50

e c m (deg)

Q04

02

0

(e)

0 10 20 30 40 50 60

Bcm (deg)

FIGURE 2. The 500-MeV quasi-elastic pn triple-scattering parameters (a) Dm,(b) Dss, (c) DSL. (d) DLs, and (e) DLL The solid curves are phase-shift predictions(solutionWI84).

References

1. M. L. Barlett, G. W. Hoffmann, J. A. McGill, R. W. Fergerson, E. C. Milner, J.A. Marshall, et al., Physical Review C 30, 279 (1984).

2. M. L. Barlett, G. W. Hoffmann,J. A. McGill, B. Hoistad, L. Ray, R. W.Fergerson, et al., Physical Review C32,239 (1985).

3. R. A. Arndt, L. D. Roper, R. A. Bryan, R. B. Clark, B. J. VerWest, and P.Signell, Physical Review D 28,97 (1983).

46

4- — pB pT (^ I nfl pT /-. r N r N *-N.N.0~ ^ r N r NN ^N.

1 3- PT

N»C0,NN,N+- PTNC0,N,N

N CN.O.N+ - PBN PT

NN CN,NN,N ,

- PBNPT

NCN,N,N ;

for 5-polarized beam:

- I — pT AT _I PT AT

- PTNN CS,NN,S+ - PT

N CS.N.S_3

2

l(oN)/In= - PTmC0,NN,N+~ PT

NC0,N,N ,

/ < o £ > / / 0 PB= CSAl + 1 PTNN CS,NN,L + - PT

N CSML ;£ 2


The analysis of the data taken withthe Af-type polarized deuteriumtarget at HRS in rb" summer of 19f 3is now complete. • he connectionsbetween measured and deduced oh-servables can be written

EXPERIMENT 685 — HRSMeasurement of Third-Order SpinObservables for Elastic pdScattering at 800 MeV

for /V-polarized beam:

nT

UCLA, Los Alamos, KEK Laboratory,Hiroshima Univ., Kyoto Univ., Univ olEducation in Japan, Univ, olMinnesota, Univ. of Texas at Austin

Spokesmen: G. J. /go and M. Bleszynski (UCLA)

47


and for /-polarized beam:

_30 2 '

/ < o S > / / 0 P f = Q , o , s + - PTNNCL,NN,S+^ PT

N CL.N.S

l(aN)/lo = P + - pTm CO,NN,N+ - PT

N CO,N,N

l(oL)/I0 Pf= CLAL + - PTm CL,NN,L + - PT

N CLML

Here, PBN, PT

N, and PTNN are beam

and target, vector and tensor polariza-tion, respectively, in the vertical (N)direction. The A'/s are the proton anddeuteron analyzing powers and P isthe induced proton polarization. /„ isthe yield one would observe withunpolarized beam and target, / is thecorresponding quantity withpolarized beam and target, and (oz)is the polarization of the scatteredproton beam as measured with theHRS focal-plane polarimeter(5= sideways, N= vertical, andL = along the beam direction). TheCWt's are the two- and three-spin observables that one wishes to obtainfrom the measurement, where / denotes the polarization direction ofthe incoming beam;/ the polariza-tion of the target; and k, the polariza-tion of the scattered beam (i,j, ork = 0 denotes unpolarized incomingor unmeasured outgoing polariza-tion).

The polarizedtarget setup is de-scribed in earlier LAMPF Progress Re-ports. The analysis of the data is dis-tinguished from that of a conven-tional HRS spin-rotation measure-ment only by the presence of the 10-kG holding field of the polarizedtarget. This strong magnetic fieldcaused a bend in the horizontaldirection of the 800-MeV protonbeam of 5.0° and a proton spinprecession of about 17°. This spinprecession made necessary correc-tions to the measured values of theCIJik's of up to 1.0. Figure 1 (a)- (g)shows the new variables we wereable to extract from the measure-ment. The solid lines are theoreticalpredictions from nonrelativistic mul-tiple-scattering calculations by E. andM. Bleszynski.

There are no tensor observablesamong the deduced quantities. Witha deuteron vector polarization of 0.3or less, the residual tensor polariza-tion is less than 0.07; no tensor ob-servables could be extracted withuseful accuracy.

48

0.4 -

e °-2

x

( j 0.0

-0.2

0.T

0.8

». 0.6

J" 0.40 2

0.0

02

-I

• o.oin

O

•0.2

0.6

0.4n• I 0.2at

0.0


-0.210.000

-0.2 -

0.000 0.050 0.100 0.150

-t (GeV/c)

0050 0100 0.150 0.200

-t (GeV/c)2

FIGURE l(a) (g) Deduced two- and three-spin observables tor elastic pd scatteringat 800 MeV

49

RESEARCH


Calibration of the DeuteronTarget Polarization by theDeuteron Magnetic Resonance(DMR) Signal Asymmetry

The area of the deuteron magneticresonance (DMR) signal is (nearly)proportional to the deuteron vectorpolarization. One way to calibrate theproportionality constant is to exploitthe asymmetry of the DMRsignallineshape. This asymmetry determinesthe intensity ratio of the transitionsbetween the magnetic substates ofthe deuteron. Assuming that all deu-terons have a common spin tempera-ture, the polarization then followsfrom the measured intensity ratio.Following is a brief description ofthis method that we developed fordetermining the deuteron targetpolarization in Exp. 685.

It has been demonstrated1 that theassumption of a common spin tem-perature Ts for the deuteron spin inthe target sample is valid. The rela-tive populations p+,pa, and />_ of themagnetic substates m = +1,0, — 1 arethen determined by a Boltzmann dis-tribution,

and Boltzmann constants, respec-tively. The ratio r, defined by thisequation, can now be extracted fromthe DMR-signal line shape thanks tothe interaction of the deuteron quad-rupole moment with the molecularelectric-field gradient. This interac-tion shifts the substate levels, de-pending on the orientation of themolecule with respect to the mag-netic field. The DMR signal thereforeconsists of two peaks correspondingto the two transitions

and

w = 0 ^ m = - l .

The two peaks overlap each otherbecause the molecules are orientedisotropically. The transition in-tensities 1+ and /_ are proportional tothe population differencesp+ — p0

andpo ~ P-y respectively, and theirratio turns out to be

4 p+-p0 r-\

P+ Par= - = -

Pa P-

where v is the deuteron Larmor fre-quency and h and k are the Planck

Hamada et al.z have analyzed therather complex structure of the DMRsignal for fully deuterated pro-panediol, the target material that weused in our experiments, and derivedthe general mathematical functionfor its line shape. One of theparameters of this function is theratio r, which thus can be obtained byfitting the DMR signal. The vector

50


and tensor polarization follow, then,from the normalizationp+ + pn + p_ = 1 and from Eq. (1),

Pz s p+ - p_ = -r - 1

r+ r+

and

r" — li

r + r+ 1

A first attempt to fit the DMR sig-nal, following the suggestion ofHamada et al., failed. The fits werequite poor and the results inconsis-tent (large discrepancies betweenthe area/polarization ratios forpositive and negative signals). A de-tailed analysis finally showed that theline-shape function used in the fit-ting lacked two essential ingredients:

1. In the paper of Hamada et al., itis implicitly assumed that theDMR signal has the same shapeas the absorption part x" of the

magnetic susceptibility, thusneglecting the dispersion partX*. However, it turns out that x'causes quite significant effectson the signal shape, as has alsobeen demonstrated recently byKiselevet al.3

2. To obtain consistently good fitsfor both positive and negativesignals, it was also necessary toaccount for the coaxial cable (oflength X/2), which connectsthe DMR coil at the target sam-ple to the preamplifier.

Figure 2 shows a typical fit to aDMR signal recorded during the 1984run of Exp. 685, at a magnetic tield of2.5 T (DMRfrequency= 16.34 MHz),using a constant-current parallel res-onant circuit. The dashed curve rep-resents the base line, that is, the volt-age signal in the absence of DMR(X' = x" = 0). The polarization re-sulting from this fit isp = —0.348. Weestimate the uncertainty in thepolarization, determined by this fit-ting procedure, to be less than 0.010.

FIGURE 2 Fit to a deuteron magneticresonance (DMR) signal recorded duringthe 1984 run ol Exp 685. The dashedcurve represents the base line, that is, thevoltage signal in the absence ol DMRThe deuteron polarization obtained Iromthis fit is —0.348. The horizontal axisgivas the difference to the DMR fre-quency of 16 34 MHz

References

1. M. Borghini and K. Scheffler, Nuclear Instruments & Methods 95,93(1971).

2. O. Hamada et al., Nuclear Instruments & Methods 189,56l (1981).

3. Y. F. Kiselevet al., Nuclear Instruments & Methods 220,399 (1984).

51

RESEARCHNuclear and Partcte Physics


Measurement of Cross Sections andAnalyzing Powers for Elastic andInelastic Scattering of 400- to 500-MeV Protons from "C

LOS Alamos, ijniv o\ Minnesota. ArizonaState Univ . Univ ot Couth Carolina,tjnu. ol FVunsvlvcinici. Univ (>l ln<as

Spokesman: M. Plum (Los Alamos)

During a 1 week period in August1984, HC(/>,//) data were obtained forl i angles, 375° < 91;ib < 28.0°, at anincident energy of Ep = 497 MeV.The salient features of most types ofangular distributions are containedwithin this angular region, One ofthe primary objectives of this experi-ment was to measure an angular dis-tribution for the cross section andanalyzing power for the 6.90-MeV

0 state. However, the thick MC target(170-mg/cm2 14C-12C powder and 45-mg/cm2n;"Ni foil windows) limitedthe resolution to about 280 keV, so aclean observation of this state was notpossible. Most other states below 11 •MeV excitation are resolved, and dataanalysis is proceeding for these andall other resolved states.

In addition to the MC target, 12C andnMNi targets were required to subtractthese impurities from the 14C spectra.A sample spectrum, with the 12C andn!ItNi subtracted, is shown in Fig. 1.The peaks at -0.39- and 5.76-MeVexcitation are due to unexpectedcontributions from 16O.

4000

3200

2400

S 1600oO

600

16O Ground State

14C Ground State

l4C(p,p')1' lC*497-Meveiab=16.0°

Spin Down

4 6 8 10 12 14 16 18Excitation Energy (MeV)

FIGURE 1 Sample spectrum with I2C and ndlNi subtracted

52

BESEABCH


The response of nuclei tothe spin^isgspin fields

(where q is the momentum transfer)holds general interest for understanding the properties of hadronicmatter. The transverse (a X q) andlongitudinal (c • q) response func-tions have simple connections to theexchanges of p and iz mesons between nucleons and betweennucleonsand A isobars, and henceare very relevant to current investiga-tions into the effects of the isobar onnuclear properties. Beyond this thereare many issues connected with thespin-isospin responses that carr\r overinto the discussion of the role ofquarks and gluons in describing nuclear properties and interactions.One such issue is the interpretationof the European Muon Collaboration(EMC) effect.

The experiment reported hereuses a new and general technique forthe measurement of the spin-depen-dent response function. It relies onmeasurement of a complete set ofpolarization transfer observables andis applicable, in principle, to nucleoninelastic scattering or charge-ex-change reactions for the entire q-mresponse surface, including discretestates and the continuum. In this report we present data derived fromSOO-MeV proton scattering for boththe transverse and spin-longitudinalresponse functions for calcium andlead at a momentum transfer of1.75 fm~" for a range of co from 20 to100 Me V. Some of the data have beenpublished in a previous letter.1

The principle of the experiment issimple. For targets of 2H, Ca (natu-ral), and Pb (natural), one measuresspin-flip probabilities (SFPs) thatbear a simple, although modeldependent, relation to the spin-isospinresponse functions. One then looksfor differences in these observablesbetween 2H and the heavy nuclei.Deuterium is assumed to be a freeneutron-plus-proton target andhence free of any collectivity thatmight occur in the heavy nuclei.

As in the earlier reporting of theexperiment, we find no difference inthe longitudinal SFP between theheavy targets and deuterium. Thenew data have higher statisticalprecision and thus weigh even moreheavily against pionic collectivity.

The major theoretical emphasis ofthis work has been to analyze the datawith the best theoretical model avail-able—the semi-infinite slab model ofBertsch, Scholten, and Esbensen.23

Beyond this we have examined sev-eral corrections to the model thathave been discussed in the literaturebut not considered quantitatively.Specifically these are

• spin-dependent distortion effects,

• kinematic effects in the 2H data,and

• double scattering.


Continuum Polarization Transfer in500-MeV Proton Scattering andPicnic Collectivity In Nuclei

Los Alamos, Indiana Univ. CyclotronFacility, Argonne

Spokesmen: T. A. Carey and J. B. McClelland(Los Alamos)

Participants: L B. Rees, J. M. Moss, K. W. Jones,N. Trtnaka, A. D, Bacher, and H. Esbensen

53

RESEARCH


The conclusion based on the com-plete analysis is that no evidence exists of pionic collectivity in nuclei. Amajor consequence of this is thatthere are no excess pions that couldaccount for the low-A-EMC effect.This is clear from a comparison ofseveral theoretical calculations toboth our data and the EMC data. Thenuclear-structure model, identical

for the calculation of both data sets,contains a parameter g", which scalesthe degree of pionic collectivity. Fig-ures 1 and 2 show that the calculationg = 0.55, which gives a reasonableaccount of the EMC experiment, failscompletely to account for our data.Thus one is forced to consider moreseriously the quark-level models ofnuclei that have been proposed toexplain the EMC effect.

J

2

0

i

-

0.0 05

9

A

KM2

l

1 i • i

-

i

. i

0 20 40

i

i

10q

1 1

8 1i

60CO

i

i

15

i

80(MeV)

—

2.0

1 * 1 '

Pb}C o *

• .T100 120

-

2.5

-

-

-

MO

FIGURE 1 The ratio ol spin-longitudinal to spin-transverse response lunctions withg' =0.55 (dot ed line), 0.7 (dot-dashed line), and 0 9 (solid line).

54


FIGURE 2 The 4-corrected ratio ol F\on structure tunctions from the EMC and SLACas a function of the scaling variable x. The curves are semi-infinite-slab calculations,asm Fig 1

References

1. T. A. Carey eia\., Physical Review Letters 53,144 (1984).

2. G. F. Bertsch and O. Scholten, Physical Review C 25, 804 (1982).

3. H. Esbensen and G. F. Bertsch, Annals of Physics 157,255 (1984).

55

RESEARCH



Characteristic Dlrac Signature InLarge-Angle Elastic Scattering at500 MeV

Los Alamos, Univ of Texas at Austin

Spokesmen. G. W. Hoffmann and M. L Barlett(Univ. ol Texas at Austin)

VIRTUAL-PAIR CONTRIBUTION

N p N

I VWWWV4

i rwvwwv i

N pTARGET BEAM

NTARGET

FIGURE 1 Virtual-pair p r o c e s s involving

a beam proton and two target nuc leons

The success13 of the relativistic im-pulse approximation (RIA) in de-scribing 500-MeV pnucleus elastic-scattering observables is due to theautomatic inclusion in the Diracequation of virtual-pair processes involving the beam proton and twotarget nucleons. This process, some-times called the Z diagram, is shownschematically in Fig. 1.

Recently, Hynes, Picklesimer,Tandy, and Thaler4 reported resultsof momentum-space calculations thatsuggested a characteristic Diracsignature would be seen inlarge-angle /(-nucleus elastic analyz-ing-power data. For the center-of-momentum angular range from 45 to60°, nonrelativistic and relativisticimpulse-approximation (NRlAand

I

IO3

IO2

10'

Iff'

Glff2

IO3

icr4

10-5

Iff6

\ « EXP 425/433\ • EXP879

\ RtA FIT TO FIRST\ jC^V "-- XMT FIT TO FIRST

p + Co v&*~'5 0 0 MevElastic Differential Cross Section

-

(a) .

30°30°

_

"* f

10 20 30 4 0 50 60

EXP425/433EXP 879

RIA ---KMT

60

FIGURE 2 Large-angle 500-MeV p-40Ca (a) cross-section data and (b) analyzing-power data obtained in Exp 879 compared with RIA (solid curve) and NRIA (dashedcurve) predictions (KMT indicates results from Kerman-McManus-Thaler )

56


RIA) approaches predicted extremedifferences in AY. In fact, near 55 ° theNRIA analyzing power was approx-imately + 1, whereas the RIA analyz-ing power was approximately —I.This signature was claimed to be in-sensitive to other uncertainties as-sociated with the calculations.4

Experiment 879 extended the 500-MeV />-40Ca elastic cross-section andanalyzing power data to a center-of-momentum scattering angle of 60 ° toprovide data that would confirm ordisclaim the Dirac signaturehypothesis. The data are shown inFig. 2(a) and 2(b). Interestingly, thecharacteristic diffractive structureseen in both the cross section andanalyzing power of the earlier dataset (angular range from 5 to 30 °)

continues out to the largest momen-tum transfer. This is in contrast to thepredictions of Ref. 4, where thepredicted diffractive pattern changesabruptly and qualitatively for angleslarger than about 30°. The solid inddashed curves are standard RIA a?dNRIA predictions, respectively, madeusing coordinate space codes. In thisinstance, the NRIA and RIA curvesare qualitatively similar io each otherand to the data at large momentumtransfer. Therefore, we conclude thatthere is no large-angle characteristicDirac signature in p-nucleus elasticscattering (experimental or theoreti-cal).

References

1. J.ShepardJ. A. McNeil, and S.J.Wallace, Physical Review Letters 50, 1443(1983).

2. B. C. Clark, S. Hama, R. L. Mercer, L. Ray, and B. D. Serot, Physical ReviewLetters 50,1644(1983).

3. B. C. Clark, S. Hama, R. L. Mercer, L. Ray, G. W. Hoffmann, and B. D. Serot,Physical Review C28,1421 (1983;.

4. M. V. Hynes, A. Picklesimer, P. C. Tandy, and R. M. Thaler, Physical ReviewLetters 52,978 (1984).

57



Development of a 0° Focal-PlanePolarimeteratHRS

Los Alamos, Univ ol Minnesota, Rutgers

Univ , Umversite Paris * l

Spokesmen: J. B. McClelland (Los Alamos) andS. K. Nanda (Univ. of Minnesota)

This experiment was to extend in-elastic spin-flip measurements, Snn,toO°. Our previous work had demon-strated the feasibility of inelasticcross-section measurements at 0" forlight- to medium-mass targets. Thiswould be an integral part of the Mlspin-flip measurements now underway to 3° at the HRS.

The considerable spin-flipstrength seen in the 90Zr(p,//) studiesat forward angles has been tentativelyidentified as being from Ml, M2, andM3 contributions, based on multi-pole decomposition using angulardistributions of a and Snn. However,the sensitivity of these measurementsis compromised because the smallestangle achievable corresponds to thepeak in the A/2 cross section at318 MeV. To gain increased sensitiv-ity to Ml contributions, it is necessaryto go to smaller momentum transfer.

Angles between 1 and 3° are com-pletely dominated by pole-face scat-tering, within the spectrometer, ofthe very strong elastic peak so that 0 °is the only other possibility. A tenfoldincrease in sensitivity to the Ml spin-flip cross section is predicted, basedon distorted-wave impulse approx-imation (DWIA) calculations ob-tained only if the instrumental back-ground can be maintained at a levelas good as at 3°.

Experiment 891 was our first at-tempt at 0° spin-flip measurements.A completely new detector systemwas installed at the HRS to accommo-date the new requirements. Smallerfocal-plane wire chambers, triggerscintillators, and a left/right scin-tillator system to detect the reseat -tered protons were installed. An ad-ditional beam-profile monitor andbeam integrator were added forenergy calibration and cross-sectionnormalization. In this configuration,the unscattered beam was clearly de-livered through the spectrometer,above all detectors and out a hole inthe detector shielding assembly.

The large overhead involved in theinstallation of new equipment, andthe substantial beam preparation andtuning required, allowed time onlyfor measurement of I2C. Figure l(a)shows the yield between 11 and18 MeV; Fig. Kb) is the spin-flipcross section in arbitrary units.Absolute normalization will be avail-able after further off-line processing.

It is clear from Fig. 1 that in-strumental background is almost en-tirely suppressed in the spin-flipcross section. The preliminary valueof Dnn for 15.11-MeV 1+, T= 1 is0.6 ± 0.1, in good agreement withDWIA calculations. Extensive non-0"elastic data were taken for systematicchecks.

We feel we have demonstrated thefeasibility for 0 ° inelastic spin-flipmeasurements using the HRS andplan to continue the program over alarge range of target masses in anattempt to cleanly identify Mlstrength in nuclei.

58

200

160

%Q120

ao

40

T

(a)

-

1

12.7

1.

• • i - i

I

_ 15

.11.

wj'lj11|lll|/

"T T —1

18C(p,D')«C*f Ep = 319-MeV 6^ =

\

I1 1

V

~\0.0°

-

400

2D

6<£200

•q

of100

(b)

-i \ 1 r -i r

_D_

110 11 12 13 14 15 16 17 18

EXCITATION ENERGY (MeV)

FIGURE! (a) Yield between 11 and 18 MeV and (b) spin-flip cross sectionin arbitrary units

10 11 12 13 14 15 16 17 18 19 20

19 20

RESEARCH


59

RESEftRCHNuclear and Particle Physics


Continuum Spin-Flip Cross-SectionMeasurements from *'Ca

Los Alamos. Umv ol Minnesota, RutgersUniv .Umv of Pans x|, Umv olGeorgia. Bngham N oung Univ

Spokesmen: S. K. Nanda (Univ. ol Minnesota), C.Glashausser (Rutgers Univ.), and K. W. Jones(Brigham Young Univ.)

The purpose of this experiment isto study the distribution of spin-flipstrength at medium excitationenergies (Ex < 40 MeV) and ground-state correlations in the doublyclosed-shell nucleus'"'Ca. Previousmeasurements on9"Zr, MV, and ™Niindicate unexpectedly large spin-Hipprobabilities up to an excitation ofabout 25 MeV at small laboratory scat-tering angles (8 < 5°).

Esbensen and Bertsch have calcu-lated the response of a semi infiniteFermi liquid to a spin-isospin depen-

dent probe.1 Collective effects wereincluded using the random phase ap-proximation (RPA); there were nofree parameters in the calculation.The results are shown in Fig. 1,where they are compared with datafrom previous measurements onl)"Zr(Exp. 66()).2 It is noteworthy that thecalculations indicate that the spin-flip cross section should be decreas-ing steadily for excitation energiesabove 20 MeV.

We have measured the spin-Hipcross section from 3 to 12° in the

FIGURE 1 Spin-llip cross section lor proton scattering Irom 90Zr at 3 5 1 The curvesare the predictions of Esbensen and Bertsch

60


laboratory, spanning an excitationenergy range from 6 to 40 MeV forproton inelastic scattering from "'Ca.The MRS focal plane polarimeterwasused for these measurements.

Preliminary on-line data are shownin Fig. 2(a) (c). It is clear from thesefigures that the spin flip crosssection is large at small angles, evenfor excitation energies up to 40 MeV.The known, strong 2~ state in 4"Ca atK. 12 MeV excitation is easily seen inthe ..pectra and has a large spin-flipcross section. The weak M1 transi-

tions at 10.2 and 12.0 MeV were alsoobserved in the small-angle data, andwe hope that values of the spin-flipcross section for these states can beextracted from the data during replay.

Study of these Oftco excitations mayimprove our understanding of 2p2bcorrelations in the ground-state wavefunction of this nucleus. A multipoledecomposition of the data is plannedto determine the strengths andangular distributions of M1 to A/3spin-flip transitions.

IS

£J- 18

$U 12

C a

I!Bo

00

OS

0.4

OJ

02

01

i-- L

i-i—<-

-

•

4 0Ca (p.p'

= .i 1 J Mex

U'll

1 '

' { i

| 4 0 C a * !

e,Ht, = 3 • ;

-

i . j -hi i 1

--

5 10 15 20 25 30 35

EXCITATION ENERGY (MeV)(al

40Ca(p.p')40Ca*

hii !

{

T 1 1~

10 1 5 2 0 2 5 3 0 3 5 * 0

EXCTTATION ENERGY (MeV)(b)

4OCa(p,p')4OGa*

= 319 MeV 6,Hl, =

' • I ' , "10 15 20 25 30 35

EXCTEATION ENERGY (MeV)(C)

Gi Rt ..' ' I 'D u ' o h a b i h i v a n d re la t i ve s p i n Nip c r o s s s e c t i o n at (a) 3 0 , (b) 7 0 ' , a n d ( c ) 12 0 "

References

1. H. Esbensen and G. Bertsch, Annals of Physics 157, 255 (1984).

2. S. K. Nand. C. Glashausser, K. W. Jones, J. A. McGill, T. A. Cary, J. B.McClelland, etal., Physical Review Letters 51, 1526 (1983).

61

RESEARCH


EXPERIMENT 487"— LEP

Measurement of the E2 ResonanceEffect in Plonlc Atoms*

Univ ot Mississippi; LOS Alamos,Techmsc'ne Univesitat in. Munich,Get many, Univ ot VVvoming

Spokesmen: J. Reidy (Univ. of Mississippi) sndM. Leon (Los Alamos)

Measurements on the x raysemitted by pionic atoms have provided the principal means of study-ing the zero-energy pionnucleus interaction. A negative-pion incidenton a target slows down and is eventu-ally captured by a target atom. Thecaptured pion then cascades downthrough the pionic-atom levels, atfirst emiUing Auger electrons andlater pionic x rays. Near the end ofthe cascade the strong short-rangepion-nucleus interaction comes intoplay. This is reflected in changes inthe intensities, energies, and widthsof the observed x-ray lines comparedwith what would be observed in apurely electromagnetic cascade.These x-ray data are used for de-termining semiphenomenologicaloptical potentials that give goodagreement with most of the x-ray dataand that are consistent with the op-tical potentials used to describe low-energy pion-nucleus scattering.

However, the strong-interactioninformation derived from x-raymeasurements comes from ratherlimited regions of Z for each pionic-atom level (Is from Z < 11, 2p from8 < Z< 33, 3rffrom39 < Z < 60,and 4/from Z > 67). The reason forthis is that for a given nucleus theobservable x-ray lines terminaterather abruptly at a "last line" as theoverlap with the nucleus and hencethe absorption widths increase. Al-though it clearly would be desirableto test the optical potential for levelswith greater overlap with thenucleus, this is not generallypossible, so these levels stay hidden.

A method to probe a few examplesof such hidden levels, the £2 nuclear-resonance effect, was proposedby Leon. This effect occurs when anatomic deexcitation energy closelymatches a nuclear-excitation energyand the electric-quadrupole cou-pling induces configuration mixingof the two states. A pion in the («,8)state (with the nucleus in its groundstate) is also partly in a («',£--2) state(with the nucleus in its excitedstate). Because the (w',8—2) stateatomic wave function has a greatlyincreased overlap with the nucleus,even a very small amount of con-figuration mixing can result in a sig-nificant induced width Yind in the(«,8) state, which leads to a reduc-tion of the (n,8) —• (w—1,8—1) x-rayintensity. Measurement of this at-tenuation allows one to extract infor-mation1'2 about the (M',8—2) pionlevel. The attenuation may bemeasured with precision by compar-ing the intensities of the(«,8) — («—1,6—1) lines in the spec-tra of two isotopes, one of whichpossesses the resonance.

The purpose of the present workwas to make high-precision measure-ments on a number of pionic atomswhere the E2 nuclear-resonance ef-fect is significant. The nuclei studiedwere48Ti, 104Ru, 1I0Pd, l uCd, U2Cd,125Te, and 150Sm. We have previouslyreported results for some of theseisotopes,3 5 but the present work rep-resents new, more precise and ac-curate results for all cases. Com-parisons are made with theoreticalestimates.12 Because they give themost intense lines, we deal ex-clusively with transitions between

•Published in Physical Review C 32, 1646 (1985)

62

BESEABGH


circular states, for which S. = «—1.This work was motivated in part by

the persistent discrepancy betweenan earlier observation and the predic-tions of the optical potentials for the3p level of pionic palladium3'5

(Z = 46); this discrepancy remains,even when comparison is made withthe more complete calculations ofDubach et al.2 instead of the simplermodel of Leon.1 The 5p state is alsothe lower admixed state in UMRu and>2'Te. The highest Z nucleus wherethe hadronic contribution to the Isstate can be studied is 48Ti, and it hasthe greatest mixing. A more precisedetermination of the attenuationwould provide a sensitive test for thismixing. Dubach et al. have pointedout that pionic l50Sm is potentiallyvery interesting because a precise determination of the attenuation mayallow one to distinguish between twonuclear models for 150Sm. Of all thepionic examples of the £2 resonanceeffect, mCd and U2Cd are the moststudied.w They are important testcases because the lower admixedstate is directly observable ratherthan hidden.

The theoretical description of the£2 nuclear-resonance effect was firstgiven by Leon1 and later extended byDubach et al.2 to include mixing ef-fects that are due to the strong interaction. Let | 1) denote the state consisting of the nucleus in its groundstate and the pion in an atomic state(w,8), and | 2> the state with thenucleus in an £2 excited state andthe pion in a lower atomic state( n',H—2). Denoting the quadrupole-coupling Hamiltonian by W = H1

slrong

+ tf em, we can write for theeigenstate 11')

(1)

where a, the admixture coefficient, isgiven by

(2)A£

The complex energy difference A£ is

= e — ;y ,

(3)

where E^uc is the energy of the £2excited nuclear state, En! is the bind-ing energy of the pion in the «,£pionicatom state, and Fn 8 is thewidth of this level. From this admix-ture of the lower level, the upperatomic level now has an inducedwidth Tind, which is given by

(4)

This induced width leads to an at-tenuation of the x-ray intensity fromthe «,C state. Conversely, a de-termination of the x-ray attenuationgives information about the strengthof the coupling.

The pionic x-ray transitions thatare usually detected are those £1transitions involving circular orbits

63

RESEARCH


(maximum 2). One determines for agiven isotope the intensity ratio ofthe observed lines

r(Z,A) 3=[ n-1,8-1

./(n+l,B+l

(5)

where /(«,£ —» n—l,fi—1) representsthe measured intensity of the transi-tion between the state n,C and thestate w—1,8—1, and where Z,A repre-sents the isotope. We refer to theisotope where mixing occurs as theresonant isotope. For a nonresonantisotope Z,A', one measures the sameratio and then forms the ratio of ratios

r(Z,A)

r(Z,A') '(6)

The attenuation A is defined as thecomplement of R, that is,

A=\- R , (7)

and is a direct measure of the in-duced pion absorption out of thelevel «,C (to the extent that un-resolved noncircular transitions areabsent). One can readily show1 thatcontours of fixed attenuation are cir-cles in the (E,Y) plane (assuming thatthe mixing-matrix element is fixed)

The energies and widths of thepionic-atom states are obtained bysolving numerically the Klein-Gordon equation* with the nuclear-Coulomb potential plus the hadronicoptical potential. The potential ofSeki and Masutani,6 with parametersgiven in their Table 111 (a — 1R), waschosen. Following Leon,1 the mixing-matrix elements are calculated usingnonrelativistic point-nucleus wavefunctions (electromagnetic contribu-tion only). One then obtains predic-tions of the attenuation that can becompared with experiment.

Additional factors can contributeto the induced width, such as nu-clear-size effects, isomer shifts, nu-clear states above the collectivequadrupole state, and the inclusionof ap-wave optical potential. Dubachet al.2 have included these.

These experiments were carriedout at LAMPF using the P3 and LEPbeams. The experimental arrange-ment was similar to that described inRef. 3.

Using the fitted-line intensitiesand Eqs. (5) and (6), we determinedthe experimental values of/?. Theselvalues were then corrected for thefact that the targets were not allisotopically pure.

The relevant x-ray lines are listedin Table I. Columns 3-6 give the linesthat were analyzed in order tomeasure the attenuation. For the cad-mium isotopes the reference line isan unresolved doublet; furthermore,two lines, 5 —- 4 and 4 — 3, exhibitattenuation. The correspondinglvalues are denoted Ra and /^.re-spectively.

•ComputerprogramMATOM, from R Seki, CaliforniaSlate University at Norlhridge. 1985

64


TABLE I Relevant

Nucleus

22T'

'?44Pd

"IjTe'ISJSm

X-Ray Lines

Levels

3 d -

4 / -

4/ -

5 3 -

4 / -

(Mixed)

- Is

- 3 p

- 3 p

- 3d

- 3 p

- 4d

Attenuated Lines

3 —

4 —

4 —

5 —4 —

4 —

5 —

0

3

3

43

3

4

Energy (keV)

254

355

389

194424

500

326

Reference Lines

4

5

5

6 — 5

5

6

— 3

— 4

— 4

+ 8 — 6

— 4

— 5

Energy (keV)

88

163

i 78

105

227

176

The relevant parameters and calcu-lated results for the induced widthsare given in Table II. Row 2 gives thecalculated energy difference of therelevant pionic-atom levels using thecode MATOM. For the cadmiumisotopes the measured value is used.Row 3 lists the energy of the nuclear£2 excited state. The static quadrupole moment of the excited state islisted in row 4; two values are givenfor 110Pd that correspond to twopossible results from Coulomb-ex-citation measurements. Row 5 liststhe interaction energy of the excited-state quadrupole moment with thelower atomic state. For the odd nu-clei, which have spin 1/2, there aretwo possible orientations withj= 2 ± 1/2; the values for the anti-parallel case are given in brackets.The sum of rows 2, 3, and 5 ispresented in row 6; this correspondst o e = KeA£[seeEq. (3)]. The calcu-lated (measured for cadmium) levelwidth of the lower mixed state islisted in row 7. Rows 9, 10, and 11give the contributions to the uncer-tainty in r(3c that are due to the un-certainties in %,TjV and B(E2\), re-

spectively. (For hidden levels we as-sume a ±10% uncertainty in the shiftsand widths.) Finally, the calculatedinduced widths, with uncertaintiesobtained by adding in quadrature thevalues given in rows 9,10, and 11, aregiven in row 12. Even though thereare two values for the induced widthfor the odd nuclei, the smaller valuehas little effect on the total inducedwidth.

The results of the measurementsand comparisons with theory arepresented in Table III. Column 1lists the target composition andchemical form used for the nonreso-nant and the resonant measurement.Column 2 gives the x-ray line desig-nation for the experimental ratio,which is given in column 3. Thevalues in column 4 have been cor-rected for the isotopic abundances inthe resonant and nonresonanttargets. Column 5 presents the resul-tant attenuation values derived fromthe values in column 4. Previousmeasurements are given for

65

TABLE II Summaw

ROA

7

2

3

5

6

8

9

10

12

Mi/.ed levels

E^keV)

Qnuc

Eo(keV)

- r r f S . IkeV)'

isr.ivev,

[SFn^ir , (eV)

[Sr^ jg^ (eV)

r,rw

c Parameters arid Caic4 eTi

3o-1 s

-1029 5 + 37 5

983 5 ' 2 + 0 002

0 26 ± 0 08

0 0

-46 3 ± 37 5

84 55 ± 8 46

0 072 ± 0 003

+0 775

- 0 387

+0.003

-0010

+0 030

- 0 030

jiated Mesults tor theiO4PlJ

4/-3p

-346 01 ± 0 98

358 02 ± 0 07

- 0 70 ± 0 08

- 1 45 ± 0 17

10 56± 1.00

22.28 ± 2 23

0 834 ± 0.044

+0 11

-0 09

+0 01

-001

+0 06

-0 06

••3 «;?

induced .Vidths110pa a

4/-3P

-373 41 ± 1 52

373 81 ± 0 06

- 0 72 ± 0 14

(-0 47± 0 03)

-1 71 ± 0 33

(-1.11 ± 0 08)

-1 31 ± 1 56

(-0 71 ± 1 52)

25.54 ± 2 55

0 91 ± 0 06

-rO 04(+0 0)

-0.09(-0 07)

+0 29

- 0 22

+0 18

- 0 17

9 R9 + 0 - 3 4

2 6 2 -0.29

(2.65 ! ° 03

24

g

n ' C d D

og-3d

-618 711 ± 0 034°

620 2 ± 0 4

- 0 2 + 0 2e

-0.15 ± 0 15

[+0 26 ± 0 26]

1 34 + 0 43

[1 75 ± 0 48]

1.638 ± 0 0833

0.126± 0017

+1.72[+0 13]

-0.98[-0 06]

0 06[+0 10]

- 0 06[-0 05]

+0 40[+0 03]

- 0 50[-0 02]

\ r +017

J [ - 0 08

5g-3a

—618 r 1 1 ± 0 034a

617 494 ± 0 097

—0 37 ± 0 04

- 0 285± 0 031

- i 502 ± 0 107

1 638 ± 0 083d

0 484 ± 0 004

+0 56

- 0 48

+0 12

- 0 14

+0 04

- 0 04

4 73 + 0 5 7

- 0 50

' 2 S 1 e L

4r-3p

-460 36 + 3 42

453 387 ± 0 011

0 2 ± 0 2e

- 0 69 + 0 69

[2 19± 2 19]

2 34 ± 3 49

5 22 ± 4 06]

38 81 ± 3 88

0 158± 0 005

+0 02[+0.006]

- 0 08[-0 009]

+0 14[+0 007]

- 0 11 [-0.066]

+0 04[+0 002]

- 0 04[-0 002]

1 25 ± 0 15

-336 74 + 0 59

333 95 ± 0 01

-1 28 ± Or.

0 90± 0 08

-3 69 ± 0 60

6 67 ± 0 67

1 33 ± 0 02

+0 33

- 0 26

+0 01

- 0 02

+0 03

- 0 02

. ^ +0 33

—0 26

?leat

and P

a

0QTl

•<WO

aSee Nuclear Data Sheet tor explanation ol two possible O values, values in parentheses correspond to smaller Q value

^Values in prackets correspond to the quadrupole moment and orpital angular momentum Peing antiparatlel, olher values are for the parallel casecUncertainties are assumed to Pe 10% of the strong-interaction energy except as noteddMeasured values are taken from Ret 7eAssumed value is Irom systematics of neighboring nuclei'Uncertainties are assumed to Pe 10% ot the width except as noted9Uncerlainties are obtained by summing m quadrature rows 9. 10, and 11

RESEARCH


TABLE III Results ol Measurements and Comparisons with Theory

Present Results

Target Pan Lm^s Compared

3—24 — 3

4—3

Ffa°"Previous Resultsa Theory

Aa(%) Aa(%)

na,104R

rBtJlOp^

0 955 ± 0 010 0 941 ± 0 013

09!3±0014D 0897±0016

Z I

4 — 3

o— o + 3—»6

5 — 4

nat.112,C d 0

6—5

5

4

6—5

4

5

5

+ 8—6

—- 4

+ 8—6

—* 3

+ 8—6

— 3— 4

— 4

0 860 ± 0 007

0 908 ± 0 007

j = O922±OO13

0 624 ± 0 005

i = 0 710 ± 0 011

0 840 ± 0 008

0 780 ± 0 007

0818±00l4

0 528 ± 0 006

0.623 ± 0 012

0 994 ± 0 012 0 994+0 012

6 — 50 888 ± 0 007 0 868 ± 0 008

5 9+13

10 3 ± 1 6

16.0 ±0 08

22 0 + 0 7

= 18.2 ± 1.4

47 2 ± 0 6

= 377±1 2

06± 1 2

13 2 ±0.8

1 9± 32 120+ 1 0 3

- 67

7 2± 10.5 10 5 ± 1 0

194± 28

21 8+ 3 720 4+ 3 6"

9 2 ± 598.6+ 5.7b

50.5 ± 2,9C

44 3 ± 2 2C

28 5 ± 5 832 2 ± 3 7C

140+ 34aFromRel 5 except as notedBCorrected tor targe! thickness and density dillerenc.escRelerence 7

152+ 1 3

21 1 ±32

164 + 2.8

46.0 ± 1 7

37 4 + 1 7

2 9 ± 0 3

111 + 11

comparison in column 6. Calculatedresults using the widths from Table IIare listed in column 7.

All the parameters used in the cal-culation of the induced width forulCd and ll2Cd have been measured.In addition, as described in Leonet al.3 and Batty et al.,7 x-ray intensityvalues for transitions between non-circular orbits have been measured.Consequently, one can constrain theinitial distribution. Figures 1 (a) and1 (b) give a plot of/^, and/^ versusthe

7—5

6—5 + 8—6

and

6-4

6—5 + 8—6

ratios for u lCd and "2Cd, respectively.The ranges for these latter two ratios,determined by Leon et al.5 and Battyet al.,7 are indicated. The upper and

67

RESEARCH


0. ISO 0.200 0.250

0.900

0.800

0.800

0700

Cd-111(5*4)

(a)

0.160 0.180 0.200 0.220 0.240 0.?60

0.150 0.200 0250

0.620

0.580

0.550

0500(b)

_L7 - S

^ 6 - . 5 * B - 6 I0.160 0.180 0.200 0.220 0.240 0.260

(-iG'JRE ' -t!«nuation •.alues ft. and Rn -.ersusthp

-5 + 3-

x - rav ' i ne intensity rat io lor (a) C d a n d ( b * " C d

lower bounds for each f^ and fy aredetermined by the range of uncer-tainty in the induced width. Thedashed regions correspond to themeasured values. The dotted lines inFig. l (b) correspond to 'he curve ob-tained by using only calculatedvalues for the x-ray paramerers inT.ible II. The calculated values givenin Table III ;>re the weightedaverages of the values determinedwith the three separate measured x-ray intensity ratios.

The excellent agreement betweenthe measured values and calculatedvalues for both u lCd and "2Cd lead usto deduce that the energy of the nu-clear-excited state in u lCd is mostlikely620.2±0.2keV.

The contour plot for iaTi is shownin Fig. 2(a). The attenuation values(in per cent) are given for each con-tour. The measured attenuationrange corresponds to the shadedarea. The elongated ellipse boundsthe region determined from the in-duced width value in Table 11. Wesee that the major uncertainty in thecalculated value is due to a largeuncertainty in e. This reflects the as-sumed 10% uncertainty in the strong-interaction contribution to energy ofthe Is state (see Table II). The agree-ment between the calculated and ex-perimental values is marginal for thiscase. One expects that strong mixingwould be significant for this 15 state,so the treatment of Dubach et al.2

f hould be more appropriate. Indeed,including strong mixing could de-crease the calculated attenuationvalue in the present case to approx-imately 4.5%, in excellent agreementwith the experimental value.

68

RESEARCHNuclear and Panicle Physics

^ zoo

£

-!O -5

i

(a)

1 1

—

i - 1 /

( l1 - \ \ II

i i

i

^ R3——

(

i

^ s . (4

i

-110- 3 ) "

-

(c)

o s-€(KeV)

8m - ISO(5-4)

(e)

-e(K»V)

\ I

-e(KeV)

50

I"V 30

20

10

1

1

1 1 1 , 1

( ' • • •

\ {^i i -TSw i -

t i

- To-(4

\\

125 '-3 )

> 1 * A " "

} , '4,1

-/: lMr

(d)

-40 -3O -20 -10 0 tO 20 30 40

-€(KeV)

FIGURE 2 Contour plots for (a) 48Ti, (b) 104Ru,(c) 110Pd, (d) 125Te,and(e) 150Sm. Each attenuation value is next to its contour Therange of experimental values is represented by the shaded region, and each calculated v 'ue with its region of uncertainty is shown bya po;nt and an associated ellipse.

69


The contour plot for 104Ru is shownin Fig. 2(b). The striking agreementbetween the simple theory and ex-periment is evident. The contour plotfor u0Pd is shown in Fig. 2(c).Inthepast a great deal of effort has goneinto trying to reconcile theory andexperiment for this case The theoret-ical calculations, even with strongmixing and unequal neutron andproton distributions, gave attenua-tion values that were too low com-pared with experiment.2 However,from Fig. 2(c) we see that even thesimple theory now gives excellentagreement with experiment. This isprimarily due to the fact that the calculated width of the 3p state usingthe parameters of Seki and Masutani6

is somewhat lower than that calcu-lated by Dubach et al.2 FromFig. 2(c) we see that a given changein y will lead to a larger change inattenuation than a correspondingchange in e. Comparison of Table IIwith the calculations of Dubach et al.shows that the values of y and e usedin their work are about 7 keV largerthan those used in the present work.

Including strong mixing in the pres-ent work would increase the theoreti-cal attenuation, which would leadonly to a marginal improvement inthe overlap between theory and ex-periment.

The same atomic levels are in-volved in '"Teas for 1(MRu and ll0Pd.The contour plot is presented inFig. 2(d). For the theoretical region,only the parameters in Table I i,which give the larger induced width,are used. Unlike the 104Ru and noPdcases, the experimentally de-termined attenuation value is nearly2 std dev from the theoretical value.This is the heaviest nucleus that in-volves the p- wave pion-nucleus inter-action on which experiments havebeen performed, and it is possiblethat for such a large A the form of theoptical potential or the values of thepotential parameters are not ap-propriate. Neutron-proton densitydistribution differences would play agreater role for 125Te than for lower-mass nuclei; this could be anotherfactor leading to the discrepancy be-tween theory and experiment.Dubach et al. did not treat odd A nu-clei, so the effect of strong mixinghas not been investigated.

The contour plot for l50Sm is shownin Fig. 2(e). The experimental valuefor the attenuation is about

70


2.5 std dev larger than the theoreticalvalue. Dubach et al. have shown thatthe attenuation can be increased to14.6% if a three level strong-mixingconfiguration is used. However, thisvalue is still about 1.5 std dev fromthe experimental value. A two-levelcalculation produces a decrease inthe attenuation.

In conclusion, the agreement ofthe experimental results for the cad-mium isotopes (where the lowermixed level is observable) with sim-ple theory is excellent, and indeedfor u lCd the data can be used to de-duce a more precise value of the(5/2)+ excitation energy. The persis-tent discrepancy between theory andexperiment for "°Pd, involving thehidden 3p level, now appears to beresolved, and the ln4Ru result alsoshows good agreement. However,'"Te, the last 3p case, does have adiscrepancy of 2 std dev. Althoughthe 150Sm value differs from the sim-ple-theory prediction ofLeon1bymore than 2 std dev, the calculationof Dubach et al.2 provides much bet-ter agreement. Finally, for the potentially very interesting case of 48Ti,more careful theoretical work isneeded fora meaningful comparison.

In summary, the basic El reso-nance mechanism is understood, butit is not clear that the effects of the

strong interaction are properly in-cluded. The present work providesexperimental values that shouldenable one to test more rigorouslythe inclusion of strong-interaction ef-fects

This work was supported in part bythe National Science Foundation,attenuation than a correspondingchange in e. Comparison of Table IIwith the calculations of Dubach et a!.shows that the values of y and e usedin their work are about 7 keV largerthan those used in the present work.Including strong mixing in the pres-ent work would increase the theoreti-cal attenuation, which would leadonly to a marginal improvement inthe overlap between theory and ex-periment.

The same atomic levels are in-volved in 125Te as for 104Ru and U0Pd.The contour plot is presented inFig. 2(d). For the theoretical region,only the parameters in Table II,which give the larger induced width,are used. Unlike the 1(MRu and U0Pdcases, the experimentally de-termined attenuation value is nearly

71


2 std dev from the theoretical value.This is the heaviest nucleus that in-volves thep-wave pion-nucleus inter-action on which experiments havebeen performed, and it is possiblethat for such a large A the form of theoptical potential or the values of thepotential parameters are not ap-propriate. Neutron-proton densitydistribution differences would play agreater role for l25Te than for lower

mass nuclei; this could be anotherfactor leading to the discrepancy be-tween theory and experiment.Dubach et al. did not treat odd A nu-clei, so the effect of strong mixinghas not been investigated.

The contour plot for 150Sm is shownin Fig. 2(e). The experimental valuefor the attenuation is about2.5 std dev larger than the theoreticalvalue. Dubach et al. have shown thatthe attenuation can be increased to14.6% if a three-level strong-mixingconfiguration is used. However, thisvalue is still about 1.5 std dev fromthe experimental value. A two-levelcalculation produces a decrease intheattenuatior.

In conclusion, the agreement ofthe experimental results for the cad-mium isotopes (where the lower

72

RESEARCHNucltar and Particle Physics

mixed level is observable) with simpie theory is excellent, and indeedfor l uCd the data can be used to deduce a more precise value of the(5/2)+ excitation energy. The persistent discrepancy between theory andexperiment for ll0Pd, involving thehidden 3p level, now appears to beresolved, and the "MRu result alsoshows good agreement. However,125Te, the last 3p case, does have adiscrepancy of 2 std dev. Althoughthe l50Sm value differs from the simpie-theory prediction of Leon1 bymore than 2 std dev, the calculationof Dubach et al.2 provides much bet-ter agreement. Finally, for the poten-tially very interesting case of 4BTi,more careful theoretical work isneeded for a meaningful comparison.

In summary, the basic £2 resonano-' mechanism *s understood, butit is not clear that the effects of thestrong interaction are properly ineluded. The present work providesexperimental values that shouldenable one to test more rigorouslythe inclusion of strong-interaction ef-fects.

This work was supported in part bythe National Science Foundation.

References

1. M. Leon, Physics Letters 50B, 25(1974), and 538,141 (i974) ;and-Nuclear Physics A260,461 (1976).

2. J. F. Dubach et al., Physical Review C 20, 725 (1979).

3. M. Leonet a!., Physical Review Letters 37', 1135 (1976).

4. J. N. Bradbury et al., Physical Review Letters 34, 303 (1975).

5. M. Leonet al., Nuclear Physics A322, 397 (1979).

6. R. Seki and K. Masutani, Physical Review C27', 2799 (1983).

7. C.). Batty et z\., Nuclear Physics A296, 56l (1978).

73

RESEARCH


EXPERIMENT 813 — L E PPlat. Charge Asymmetries for "C atLow Beam Energies on the LEPSpectrometer

Univ ot Colorado. Los Alamos, Univ olSouth Caioiina, Arizona State Univ ,Virginia Polytechnic Institute and State'Jm>.

Spokesmen: R. J. Peterson and J. J. Kraushaar;Univ. ol Colorado)

Previous pion inelastic-scatteringexperiments at resonance1 have revealed several transitions in 13C thatexhibit large asymmetries with respect to n~ and K+ scattering, The aimof Exp. 8i3 was to examine thesesame transitions at lower beamenergies where T= 3/2 amplitudesmay not be so dominant. Ofparticular interest is t h e / = 9/2+,7"= 1/2 state at an excitation of9.50 MeV. This state is due to astretched (pi/2clwl) neutron particle-hole configuration.2 At resonance,the cross section for scattering to thisstate exhibits a 9/1 ratio for 7C~ to vt+

scattering.1 Because this state has asimple and known structure, we hopethat low energy data will shed somelight on the reaction mechanism forinelastic pion scattering at energieswell below (3,3) dominance.

The experiment was performed inSeptember at the LEP channel usingthe new Clamshell spectrometer.Data were taken at an incident energyof 65 MeV at lab angles of 45,65,84,and 105°, with both7i+ and ri~ beams.In addition, we took a n~ spectrum at105° with a beam energy of 50 MeV.Characteristic spectra at a lab angle of84 ° with an energy resolution of500 keV are shown in Fig. 1. As canbe seen from the figure, we will alsobe able to obtain information aboutseveral other states, especially thequadrupole collective transitions at3.68 and 7.55 MeV and the monopoletransitio t 8.86 MeV. Broad, excitedstates are -en up to 20 MeV in excita-tion.

The data are currently beingreplayed and analyzed at the Univer-sity of Colorado at Boulder. Prelimi-nary results suggest that the ratio ofri~ to 7t+ cross sections at 65 MeV forthe 9.50-MeV state is much less thanthe 9/1 ratio found at resonance. It isperhaps as low as 2 or 3 to 1. At65 MeV, absolute cross sections willbe obtained by normalizing to theTC* D measurements of Balestri et al.3

from our spectra on deuteratedpolyethylene.

74

RESEARCH

Nucleai and Particle Physics

375

c3OO

J

65-MeVn'84°

Channel

375

oO

65-MeVrc+

84°

Channel

FIGURE'1 Spectra tor 65-MeV (a) n and(b) 7t+scattering on 13C, obtained with theClamshell spectrometer An enhancement ol ;t~ over j t+ excitation of the 9 50-MeVMA transition is observed, but this is not as great as that seen at resonant pion beamenergies

References

1. S. J. SeestromMorris, D. Dehnhard, M. A. Franey, G. S. Kyle, C. L. Morris, R.L. Boudrie, et al., Physical Review C26, 594 (1982).

2. T. S. Lee and D. Kurath, Physical Review C 22,1670 (1980).

3. B. Balestri, G. Fournier, A. Gerard, J. Miller, et al., Nuclear Physics A392,217(1983).

75


EXPERIMENT 884 — LEP

Plon Double Charge Exchange on UCat Low Energies

Los ^ I . . I " 'v> -"'it'ortj State Univ , Virginia

.•I,:*., him. Institute and HtateUmv .

Spokesmen M J Leitch and H. W. Baer (LosAlamos)

Participants: R L Burman, M. D. Cooper, J. R.Comlort, A Cui. B. J. Dropesky, G. C. Giesler,R. Gilman, F. Irom, J. N. Knudson, M. J.Leitch, C L. Morris, andD. H. Wright

' ochemadc diagram ol the

Introduction

This is the first double charge-exchange (DCX) experiment performed with the Clamshell spec-trometer. The goal is to determinethe energy dependence and mass dependenceof double-isobaric analogstate (D1AS) transitions at low pionenergies. The few previous measure-ments at low energies can be foundinRefs. 1-3.

In the 1985 runs we measured the14C DIAS transition at energies 30, 50,65, and 80 MeV, and the 4BCa DIAStransition at 35 MeV. Our measure-ments cover a much broader angularrange (from 20 to 130°) than do theEPICS measurements at higherenergies, and therefore we can deter-mine the angle-integrated DIAS crosssections.

A unique feature that distinguisheslow-energy (30- to 65-MeV) DCX re-actions from higher energy reactions(TK > 100 MeV) is the inhibition ofthe double-forward-scattering mech-anism at the low energies, i i.,j is dueto the small forward-angle, single-charge-exchange (SCX) amplitudenear 50 MeV that results from thenear cancellation of the s and ppartial waves in the rc/Vcharge-ex-change reaction. Calculations byGibbs et al.4 show that at 50 MeV suc-cessive near-90° scatterings producemost of the forward-angle DIAS crosssection, whereas at 180 MeV successtve near-0° scatterings produce most

of the 0° DIAS cross section. A conse-quence is that the average separationdistance of the two nucleons participating in the double scattering issignificantly less for 50-MeV scatter-ing than for 180-MeV scattering.1

Thus low-energy DIAS transitionshold some promise for providing amean» of study for the short-rangeAW dynamics in nuclei.

Experiment

The DIAS measurements reportedhere were made using the Clamshellspectrometer at the LEP channel. TheClamshell spectrometer is a single-dipole spectrometer with nonparallelpole faces and a flight path of about2 m. It has a solid angle of 40 msrwith a resolution of several hundredkiloelectron volts and a maximummomentum of 260 MeV/c. Aschematic diagram1 is shown inFig. 1. A trigger is provided by one ormore focal-plane scintillators (52,53, 54) and, for DCX, a front scindilator (51) in coincidence. Two x-ydrift chambers5 in the focal planeprovide the position and angle inboth x and y at the focal plane thatare used to construct the momentumof each particle. The acceptancecurve across the focal plane is shownin Fig. 2. Our group has been ex-tensively involved in the com-missioning of this spec'rometer andis primarily responsible for develop-ing its DCX capability.

The present DCX capability of theClamshell rests on the rejection ofevents with low pulse height in 52

76

RESEARCH


1 0 0 0

5 0 0

UJ

FOCAL-PLANEACCEPTANCE

- 3 0 - 2 0 - 1 0 10

~ measured local plane acceptance curve tor the Clamshell

and V3 (electrons primarily) and therejection by time of flight between SIand SI (rejection of muons and anyelectrons surviving the previous re-jection). The water Cerenkovde-tector used in our first runs to rejectelectrons was unnecessary at lowenergies because of the excellentelectron rejection by pulse heightand time of flight. During our mostrecent run it was replaced with athick (lS-cm) scintillator that stopsre's up to 70 MeV and, along with theother scintillators, gives a totalenergy determination for the parti-cles.

Figure 3 shows a plot of time offlight versus E difference, where the£ difference is the difference between the total energy deposited inthe scintillators and the energy de-termined from the bending in themagnetic field as measured by the

wire chambers (assuming a pionmass).The7t's, (i's, and e'scanbeclearly seen as separated groups. ForJt~'s, the JI group can be smeared inthe ^-difference direction because ofthe possibility of huge energy dep-ositions from stopped JT'S that"star."

Several deficiencies in this systemlimit it to angles larger than 20 ° andto energies > 15 MeV. The mostserious problem is the necessity forthe front scintillator, which providesthe excellent time-of-flight informa-tion for particle identification (PID).At forward angles its rate becomesexcessive because of decay muonsand large elastic-scattering cross sections. In test runs without this front

e

" . . . • , "

-

ELASTIC

5 10 tS 20

TWE-OF-FLK3HT (ns)

(b)OCX

S 10 IS

TME-OF-FUGHT (ns)

FIGURE 3 Scatter piot cf the variableE ditference versus time ol (light, whereE difterence = [IE, (scintillation) —!„ (Ciamshell)], and time ol Might =traiectory-corrected time ot Might be-tween S1 (entrance scintillator) and 52(local-plane scintillator) tor

(a) 22-MeV7t+elastic scattering at40°and

(b) 35-MeVDCXon4aCaat45°

77


20

>

10

Oo

OIAS

45*

_•_

so*

n nn n0 5 10

EXCITATION ENERGY IN 14O (MeV)

FIGURE 4 Spectra lor the uC(n+,n~) reaction for 30 MeV at 45 and 90° The DIAS isvirtually the only component in the spectrum.

scintillator we were unabk co seeeven the strong well-separated DIAStransition on UC at 50 MeV and 40 °.We see two possible solutions to thisproblem:

1. remove the front scintillatorand use, instead, a scintillatorplaced part way through thespectrometer in the vacuumwhere particles of the samecharge as the beam have beenbent out by the magnetic fieldso that the rate will be muchlower. We have already de-signed this system and couldimplement it next year; and

2. install a sweeping magnet at thescattering chamber similar tothat used at EPICS for forward-angle DCX measurements.

Other more straightforward modi-fications are also planned to improvethe very low energy capability andthe ^-difference PID:

1. install a thinner front and a thin-ner first-focal plane scintillatorto reduce energy loss and mul-tiple-scattering effects for thevery low energy pions, and

2. construct a layered and seg-mented stopping counter in thefocal plane to replace the

78


EXCITATION ENERGY IN14O (MeV)

FIGURE 5 Spectra lor the MC(ji+,7t~) reaction at 60 MeV (preliminary data, thisexperiment)

present 15-cm stoppingcounter. Also, further shieldingnear the scattering chamberwill be added to reduce back-grounds and singles rates.

The results presented here wereobtained in September and Novem-ber of 1985. The 14C target, which wasthe same one used in our previousmeasurements2 at 50 MeV, had athickness of 0.29 ± 0.02 g/cm2. Thedata were normalized at each angleand energy to UC elastic scatteringusing the cross sections fromRefs. 6-10. The 48Ca target consistedof a stack of four 3- by 8-cm plates,each approximately 0.115 g/cm2

thick. The ^Ca isotope enrichmentwas 91%.

Results

Carbon-14. Measurements weremade at 30,50,65, and 80 MeV. Wediscuss some of the interesting newresults.

1. A new effect we observed wasthat the states between 5 and 12 MeVare very weakly populated when thebeam energy is near 30 MeV, whereasthey are strongly populated near 65and 80 MeV. Spectra measured at 30and 65 MeV are shown in Figs. 4 and5. This is not just a momentum

79

RESEARCH


I \ [_0 40 80 120

FIGURE 6 The I4C angular distributionsat 30, 50, Uo. and 80 MeV comparedwith PIESDEX calculations (solid lines) The53 datum at 80 MeV is taken IromRef 11 * The dashed lines represent theconvenient lunction discussed in the textused to extract 0° cross sections andintegrated cross sections

transfer (q) effect. For a state at 5-MeV excitation in UO, we have thefollowing results.

30 MeV: q= 131 MeV/cat90°65 MeV: q= 113 MeV/ t a t 40°80 MeV: q= 73 MeV/c at 25°

Thus there is a larger q in the 90°data at 30 MeV than in the higher-energy data. Yet, comparison ofFigs. 4 and 5 shows that the 5- to 12-MeV region in 14O is much morepopulated at 65 and 80 MeV. Thelarge reduction in the nonanalogcross section between 65 and 30 MeVand the near constancy of the for-ward-angle DIAS cross sections overthis energy interval should be usefulin determining the relative contributions of the nonanalog and analogintermediate states for DIAS tran-sitions.

2. Figure 6 shows the measuredangular distributions together withthe fitted function AeUcoi0~u + B.These were used to obtain the 0 °cross sections, t/o/</QDIAS(0°) =A + B, and the angle-integrated crosssections,

ODIAS = 27t[2B + .4 (1 - e"a) A],

Preliminary values are given in thefollowing table:

*Add'iional information lor Figs b 8 is Irom RGilnian, University of Pennsylvania, 1935 Inforrnationon 14CislromRels 1 and2. on48Ca, fromRef 12

80

RESEARCH

Nudeai and Particle Physics

(MeV)

2 9 1

4 9 2

64.-1

/a/rf&2D1AS(0(|ib/sr)

. V

3.9> >

' °D1AS

(jib)

231

1=5.0

X

D . T l

2.312."ii

The angular distributions becomemore isouopic (X = 0) as the beamenergy is lowered.

Also shown in l:ig. 6 are calcula-tions with the optical -model programPIESDEX using the Si) MeV parametersdescribed in Ref. 13- Ii is interestingta-note that, although the second-order isoscalar and isovector

1.0

i J{b

•D

1.0

h

' 1

0

1 |11

11

100

}

t

2 0 0

Tw(lib)

\ \

0/S'DIAI

1 \- e .

StiO

•

1

1I

1-ij1-I

:

L'iG'.!RE ' t •C'iation lunct 'ons al 0 5

•p< :hp D!-'>c; stales n I J C and "IB|.\-i

Data are i ron-Reis I ; and ' 2 ex-

cept Tor the iSCa oomt at 35 MeV which

is a preliminary result from this e-.peri

parameters used are known to havestrong energy dependences that havenot been ;: luded here, the agree-ment is quite good for the 30 and 65MeV data. This may be an indicationthat the isotensor second orderparameters have little energy dependence.

3. Another interesting result isthe forward-angle excitation function. Wit! the addition of our newdata points between 30 and 80 MeV,the UC excitation is mapped outrather completely between 30 and300 MeV (Fig. 7). These data exhibitthe deep minimum between 100 and140 MeV that was predicted in someearly theoretical calculations (for ex-ample, Fig. 8of Lui and Franco").This minimum is due to the strongabsorption of pions near the reso-nance energy. The rise indo/dQDlAS(0°) at the lower energiesis in part due to the weakening of theoptical potential and the consequenthigher transparency. In addition,there may be enhancements fromshort-range AW correlations.

An important question in the studyof DIAS transitions concerns the roleof scattering through the inter-mediate-analog state. At 50 MeV it ap-pears that double scattering throughthe isobaricanalog state (IAS) ismuch less than double scatteringthrough nonanalog intermediatestates.15 At 300 MeV, it appears thatthe analog route dominates.16 APIESDEX calculation, similar to those

10.0

g

\ \

• " ^ x

10 40

C(7t+,jt~)M0(DIAS) '

\

e = o--'

1 , 1 -

00 170Tn(MoV)

FIGURE 8 Excitation lunction lor ''T-DC* to the DIAS The data are IronRets 2 and 11 except tor our preliminaryooints at 30 and 65 MeV The solidcurves are calculations with the opticalmodel program PIESDEX using potentialparameters determined in Rel 13 Thesecalculations include second order (p

2)isoscalar and isovector parameters butdo not include an isotensoi termParameters have been adjusted to give agood description ot elastic and IAS crosssections at 50 MeV on light nuclei (Noenergy dependence in these second order parameters has been included here )

81

RESEARCH

Nuclear and Panicle i

in Fig. 6 but with no isotensor p2

strength, is compared with the 14Cexcitation function data in Fig. 8.This curve essentially represents se-quential scattering through the IASand clearly shows a need for sequen-tial scattering through nonanalog intermediate states or for mechanismsinvolving short-range correlations.

Calcium-48. These are the firstDIAS cross sections measured w lowenergies for a nucleus heavier than26Mg. Cross sections were de-termined at 35 MeV and upper limitsfor 50 MeV.

1. The 48Ca spectra at 35 and50 MeV also show the substantialsuppression of the nonanalogstrength at lower energies, as wasdiscussed above for UC. The 35-MeVspectra shown in Fig. 9 can be contrasted with those for 50 MeV inFig. 10. At 35 MeV the DIAS domi-nates the spectrum with somenonanaing strength at higher andlower excitation energies. At 50 MeVthe nonanalog strength fills the spec-trum, making it difficult to observethe DIAS.

2. The angular distribution at35 MeV is shown in Fig. 11. By com-paring it with the 14Cdata (Fig. 6) we

20

16

12

1"3O 10o

-i 1 1 rDIAS

"f r

40*

nninOIAS

nnnoiinO 5 10 15 20 25 30

EXCITATION ENERGY IN 4 8 T i ' (MeV)

FIGURE 9 Specda trv ih

the e* Dec ted posit ion tor the D i - 8 are ciea' iy u

menu", data tn, - pen

82


see that the 48Ca cross sections areabout 3 times smaller than those for14C at 30 MeV. Thus, although thereare 4 times as many valence nucleonsavailable in 48Ca, the cross section issubstantially smaller. The solid curvein Fig. 11 is a PIESDEX calculationwith the same parameters as wereused for the comparison with the 14Cangular distributions in Fig. 6. Thecalculation overestimates the 48Cadata by a factor of 3. However, thisdiscrepancy cannot be taken tooseriously because the isospin-in-variant coupled-channel (IICC) ap-proach used cannot take Coulombeffects or Q-value effects into ac-

count. For 48Ca(QD1AS = -12.1 MeV)at these low beam energies, theseeffects may be quite important.Siciliano is extending the PIESDEXwork to include the effects by using adistorted-wave impulse approxima-tion (DWIA) approach thatreproduces the IICC well but canalso include Coulomb and Q-valueeffects.13

3. The excitation function for48Ca at 35 MeV is compared with thatfor l4C in Fig. 7. The 48Ca data arequalitatively similar in shape buthave a broader minimum that appearsto be at a higher energy.

EXCITATION ENERGY IN 4 8Ti (MeV)

FIGURE 11. Angular distribution lor the48Ca(rt+,ji")48Ti (DIAS) reaction at35 MeV The solid curve is a PIESDEX

calculation with the same parameters asthose used in Fig. 8. The dashed linesrepresent the convenient function dis-cussed in the text {A = 0,493, S = 1.38,A. = 5.85).

FIGURE 10 Spectrum for the 48Ca(7t+,n~) reaction at 50 MeV. The expected positionof the DIAS is indicated by the arrow (preliminary data, this experiment)

83

RESEARCHNuclear and Panicle Physics

References

1. I.Navonet al., Physical Review letters 52, 105 (1984)

2. M.J. Leitchet al., Physical Review Letters 54, 1-I82 (1985).

3. A. Altaian et al., Physical Review Letters 55, 1273 (1985).

4. W, R. Gibbs, W. B. Kaufman, and P. B. Siegel, "Proceedings of the LAMPFWorkshop on Pion Double Charge Exchange," Los Alamos NationalLaboratory report LA-1O55O-C (September 1985).

5. L. G. Atencio et al., Nuclear Instruments & Methods 187, 381 (1981).

6. B. Preedom et al., Physical Review C 23,1134 (1981).

7. M.Blecheret al.. Physical Review C 20,1884 (1979).

8. M.J. Leitch et al., Physical Review C29, 56l (1984).

9. F. E. Obenshain et al., Physical Review C 21, 2753 (1983).

10. M. Blecheret al., Physical Review C28, 2033 (1983).

11. P. A. Seidl et al., Physical Review C 30,973 (1984).

12. M. Kaletka, Ph.D. thesis, Northwestern University, Los Alamos NationalLaboratory report LA-9947-T (1984).

13. E. R. Siciliano, M. D. Cooper, M. B.Johnson, and M.J. Leitch, "Effects ofNuclear Correlations on Low-Energy Pion Charge-Exchange Scattering"(submitted to Physical Review C).

14. L. C. Lui and V. Franco, Physical Review C11, 760 (1975).

15. T. Karapiperis and M. Kobayashi, Physical Review Letters 54,1230(1985).

16. G.A. Miller, Physical Review C 2^,221 (1981).

84

RESEARCH

i ann I--'article Phvsica

At the resonance energy, the Knucleus optical potential is stronglyabsorbing. The optical absorptiondominates true absorption, the p-wave amplitude dominates the .<•wave amplitude, and the interactionis strong. Tor the most part the infor-mation obtained concerns propertiesof nuclear surfaces. In the ultra low-energy region (below SO MeV> theopposite situation occurs. The .'.•-waveinteraction is larger than the p-waveinteraction, true absorption domi-nates optical absorption, and the in-teraction is weak. In this energy re-gion the pion mean free path in thenucleus becomes comparable to theinternucleon spacing and the infor-mation obtained concerns the nu-clear interior.

In the last few years a substantialamount of data for low-energy pionsingle charge exchange (SCX) to theisobaric-analog state (IAS) has beenproduced with the 7t° spectrometer.In particular, in cycle -»1 we sueceeded in measuring excitation func-tions12 for 15N(7t+,n°) (IAS) andHC(7t+,Tt°) (IAS) in the range from 35to 65 iMeV. Also, we have measuredexcitation functions1 for39K(Tt+,n")(IAS)and12"Sn(7[+.Jt°) (IAS)in the range from -40 to 80 MeV. Datah.iVe been published for angular dis-tributions for 1SN ( Ref. 3>.-wKand48Caat 50 MeV ( Ref. -1), and for an excita-tion function for "Li (Ref. 5).

In this experiment we havemeasured forward-angle differentialcross sections for IASs for"Li(7t+,ic°),HC(7t+,7t0),15N(jt+,7C0),6nNi(it+.7c"),and12oSn(n+,K°) at 20 MeV. Also, the dif-

ferential cross sections tor the~Li(it+,Jt") (IAS) were measured at180a for 20 MeV incident beamenergy. This is the first measurementof pion SCX at 180°.

The experiment was performed atthe LEP using the TI" spectrometer,"which was set in its two-post configuration. A 1 5 m, crossed field dcseparator was used to obtain nearlypure 20-MeV K+ beam. Sufficientspatial separation of the jr., n, and obeams was achieved at a mass slitimmediately downstream of theseparator to remove all but a smallpart of the beam contaminants atthe target position. The pion flux of~ X 105 7t/s was determined directlyby a sampling-grid scintillator (SGS),which consists of a number of cylin-drical plastic scintillators embeddedin a Lucite sheet. The nominal sampling ratio R for this grid is

scintillator area

total grid area

The use of the sampling grid thenmakes it possible to monitor the in-tensity of the particle beam by count-ing individual particles at a samplingfraction, 1:100 in our case, that can behandled by conventionalphotomultipliers and their as-sociated electronics. The samplingmethod was independent of beamphase space and divergence. The


Study of the Mass Dependence ofPion Single Charge Exchange at20 MeV

s Aiar-'os oeo'ge .'.asnmgton Un

Spokesmen: F. IromandJ. D. Bowman (LosAlamos)

85

RESEARCH

Nuclear and Particle Phases

20 30KINETIC ENERGY (MeV)

40

30 -

20 -

UJ

I5 -

7Li(n*. 7i°) OAS)

20 MeV

180°

•

O 207T" KINETIC ENERGY

30 40

sampling fraction, measured with alow rate beam, agreed with MonteCarlo calculation to within 5%. Theuncertainty in the beam normaliza-tion was about 5%.

Typical Tt° spectra for the incidentbeam energy of 20 MeV on the 7Litarget at 0 and 180 ° spectrometer set-tiags are shown in Fig. l(a) and Kb),respectively. The 7t° energy resolu-tion (FWHM) in these measurementswas 3 to 3.5 MeV. A Monte Carlo sim-ulation of the spectrometer, beam,and target7 gave the angle-dependentline shapes that were used to fit thedata, and described them well. Thedecomposition of the spectra intobackground and the IAS peak for the7Li measurements can be seen fromthe solid lines in Fig. 1. The datawere fitted by the maximum-like-lihood method described in Ref. 7.

In Fig. 2 we present our prelimi-nary results for the measured crosssections at the mean acceptanceangle for each bin. The cross sectionfor7Li(Tt+,7t0) (IAS) at 180" is as largeas the cross section for this reaction at0°. This result is remarkable andtotally unexpected.

The A dependence of the forward-angle differential cross sections tothe IAS is presented in Fig. 3. Theshape is well represented by a formg{N— Z)A~a. The fitted parametersare g = 698.4 \ib/sr and a = 0.92.This result is contrary to what onemight expect from the transparentlimit, which is that the cross sectionsimply scales with the number of ex-cess neutrons (N— Z).

FIGURE 1 Measured Jt° spectra for the 7L\{K+,n°) (IAS) react ion at 20 MeV with the

spectrometer setting at (a) 0 ° and (b) 180° The sol id curve s h o w s a fit to the IAS.

86

RESEARCHNuc it.ai .md Particle Physics

Currently, there are no SCX data at180 °, with the exception of our measurernent of 20-Me\'\i( n:\jt1''). Recently, measurements" of large -angleelastic scattering at KIMCS have dem-onstrated that the firstorder opticalmodel calculations fail to reproducethe large angle data. These studiesshow that higher order terms in theoptical potential have their greatestinfluenc-.1 at back angles. To under-stand the effect of the isovect >r

higher order terms and to establishthe systematic^ of the back angleSCX at low energies, a larger body ofthe data is needed. The present workshows that the 180° SCX cross sections to the IAS are large enough tobe measured. Future experiments areplanned to further map out the massand energy dependence of lowenergy SCX at back angles.

1CJ

io3

IO2

IO1.

IO*

10*

IO1.

10*

10':

IO2

,0'

' 1 1 '

._ fFf

r|lf

" , 1 , 1 ,3 40

i ' ' ' 1 i ' i 1

l20Sn j

-

60Ni - i

-

1 , I , 1 , 1 , 1 , 1 ,80 120 160

FIGURE 2 Angular distribution for theisobanc-anaiog states (lASs) ol'Ll(7I+,JtO),14C(TC+,7UO),'5N(jt+,JtO),6ONi(jt+,7to),and'2OSn(jE+,rc°)witha2O-MeV pion beam

liT|M1

^ ^

•a

1(f

102

10'

1 0 1

- A(ir*.n°) (IAS) -

V 20 MeV

"1 Ul

1 \

I I

I

; \ ;

; 0=0.92 :

» BO

A

FIGURE 3 The A dependence ol the for-ward-angle (7i+.;i0) differential cross sec-tion to the isobaric-analog state nor-malized with the neutron excess [N — Z)The solid line represents a lit to the datawith the gxA~a function

87

RESEARCHUnclear .-ti"'i:i F n'

References

1. F. Iromet al., Physical Review Letters 55, 1H62 (1985).

2. J. L. Ullman et al., "Pion Single Charge Exchange on HC from 35 to295 MeV" (submitted to PhysicalRevieu Letters)

3. M. D. Cooper et al., Physical Review Letters 52, 1100 ( 1984).

-!. M.J. Leitchet al., 'Tion Single Charge tixchange Angular Distributions al7; = 48 MeV," Physical Review C 33,27H-2H6 (1986).

5. F. Irom et al., Physical Review C31, 1464 (1985).

6. H. W. Baeret al., Nuclear Instruments & Methods 180, 445 (1981).

7. M. D. Cooper et al., Physical Review C 25,4W (1982).

8. K. S. Dhuga et al., Physical Review C 32, 2208 (!985).

88

RESEARCH

Hdi ancl Particle l-'iiysics

We have studied the165Ho(7t+,Jt")1MErisobaric analog-state (IAS) reaction at energies nearthe KN (3,3) resonance as a test of thefeasibility of the full experimentplanned for Exp. 899, which is designed to make :i < 15"-o determina-tion of the shape of the neutral-matterdistribution in ""Ho. This studyalso compared the IAS reaction on*Ho, which has a very deformednucleus, to previous work' where thesystematics of the IAS reaction wasestablished using primarily sphericalnuclei. The forward-angle cross sec-tions for "*Ho are consistent with thesystematics, thus supporting thegeometric model2 of pion singlecharge exchange.

Angular distributions from 0 toabout 20° at incident pion energiesof 100,165, and 230 MeVweremeasured using the JI° spectrometer,which performed well after being re-furbished during the 1985 shutdown.The target was amorphous holmiummetal with a total areal density of2.80 g/crn2. The technique of targetcompensation3 was used to minimizefinite target-thickness effects. Al-though the rc° spectrometer is notcapable of resolving excitation to ad-jacent components of the lWHoground-state rotational band, the ob-served energy resolution of 3.2 to3.5 MeV is sufficient to discriminatebetween a strongly populated IAStransition and one whose isobaric-analog strength is widely dispersed.

The 100- and 165-MeV data wereeach divided into three angular binsof roughly equal acceptance, but a

lack of statistics for the 230-MeV dataallowed only a single bin encompassing the entire acceptance. The forward angle 7t" kinetic-energy spectrum at 165 MeV is shown in Fig. 1.The IAS is strongly populated, as it isfor the other two energies. Peak areaswere extracted using a fittingroutine1 method of maximum likelihood based on I'oisson statistics,with monoenergetic ft" line shapescalculated by a Monte Carlo routine'that also determines the spec-trometer solid angle. The results ofone such peak extraction are shownin Fig. 1 as two smooth curvesrepresenting the background fit andthe total fit, respectively. Differentialcross sections were calculated in theusual manner.

EXPERIMENT 8 9 9 - - L E P

Angular Distributions for themHo(7t .TtT'Er Reaction to theIsobarlc-Analog state at 100,165,and 230 MeV

Arizona State Univ , Los Alamos, NationalBureau ol Standards

Spokesmen: J. N. Knudson and J. ft. Comfort(Arizona State Univ.) and H. W. Baer (LosAlamos)

90

80 - e5Ho(n+17T

0)165Er (IAS)„ . Tn = 165 MeV0 0 70 h 0 = 4.0°

— 7T° Line-shape fit

U)

zo(J

r^ifusj-^ „,

100 120 140 160 180 200

7T° KINETIC ENERGY (MeV)

FIGURE 1 Kinetic-energy spectrum of Jt°'s produced in 165Ho(7i+,jt°) lor7", = 165 MeV The smooth curves are (he result of a fit using a Monte Carlogenerated line shape

89

RESEARCH

\udear and particie Priv

ic

,p

••§

ION

,

i—

uLJ

inmUlOcco

Eu

0.1

165

J

•T i i i r

HO(TT+,7T°

1

I•1

\

100 MeV

165 MeV

230 MeV

1

5

—1 1 | 1 1 1 1 -

)'65Er (IAS) !

II :

I "1

K)

(deg)

5

piGURE 2 Angular distributions of ail-ferential Cross sections 'or 16sHo(7t+ 7t°)ro 'he isobanc-ana'ug state m "s5Er Erroroars indicate statistical uncertainties

The calculated cross sections areshown in Fig. 2. The error bars rep-resent only the statistical uncertain-ties in the experiment. Normalizationuncertainties are 12% forthe 165- and230-MeV data and 16% tor the 230-MeV data. These angular distribu-tions were extrapolated to 0° by litting them to linear functions of c/2

and cos"9 and averaging the results at9 = 0".

In Fig. 3 the extrapolated crosssections are shown along with theearlier n° IAS cross sections1 at 0°.These earlier data established the

systematic behavior of the IAS reac-tion on the nuclei as a function ofN- Z and A. The results of the l65Hoexperiment are consistent with theestablished systematics. This impliesthat the same physics applies to boththe undeformed nuclei and thehighly deformed 1MHo—that is, thatihe strong-absorption model,6 whichforms the basis of the single-charge-exchange (SCX) systematics, appliesto deformed nuclei as well as tospherical nuclei.

These l65Ho SCX data also establishthe feasibility of the full experiment,

FIGURE 3 Extrapolated 0° cross sections, divided by neutron excess, lor previouswork (Ret 4, solid dots) and this work (open circles) as a function ol mass number AThe nuclei reported m Ref 4were7Li, 14C, 1 80, 6 0Ni, 90Zr, 120Sn, 140Ce, and208PbError bars represent statistical as well as normalization uncertainties

90

RESEARCH


whose aim is to determine the dis single-crystal l65Ho sample. The spectribution of neutral matter at the nu- trum shown in Fig. 1 is consistentclear surface. The full experiment, with our ability to measure the asym-based on the theoretical work of metry to <10%, which will allow aChiang and Johnson,6 will attempt to determination of the shape of themeasure an asymmetry among dif- neutral-matter distribution to <15%.ferent orientations of an aligned,

References

1. U. Sennhauser, H. Piasetzky, H. W. Baer,J. D. Bowman, M. D. Cooper, H. S.Matis, H.J. Ziock.J.Alster, A. Erell, M. A. Moinester, and F. Irom, PhysicalReview Letters 51,1324 (1983).

2. M. B.Johnson, Physical Review C 22,192 (1980).

3. S. Gilad, Ph.D. dissertation, Tel Aviv University, 1979 (unpublished).

4. M. D. Cooper, H. W. Baer, J. D. Bowman, F. H. Cverna, R. H. Heffner, C. M.Hoffman, N. S. P. King,J. Piffaretti, J. Alster, A. Doron, S. Gilad, M. A.Moinester, P. R. Bevington, and E. Winkleman, Physical Review C 25,438(1982).

5. H. W. Baer, R. D. Bolton, J. D. Bowman, M. D. Cooper, F. H. Cverna, R. H.Heffner, C. M. Hoffman, N. S. P. KingJ. Piffaretti,J. Alster, A. Doron, S.Gilad, M. A. Moinester, P. R. Bevington, and E. Winkleman, NuclearInstruments & Methods 180,445 (1981).

6. H. C. Chiang and M. B.Johnson, Physical Review Letters 53,1996 (1984),and Physical Review C 51, 2140 (1985).

91

RESEARCHNuclear and Partiae Phvscs

EXPERIMENT 645Area

Neutrino

Search for Neutrino Oscillations atLAMPF

Orno Orate 'Jn.w- Argonne National L.ab

Caitecn i_3>Atence Berkeley Lab LOS

Alamos. Louisiana State L'ni\-

Spokesmen. T. Y. Ling and T. A. Romanowski(Ohio State Univ.)

Participants: ft W. Harper, J. W. Mitchell, E. S.Smith, M. Timko, S. J. Fieedman, J.Napolitano, B. K. Fujikawa, ft D. McKeown, K.T. Lesko, E. B. Norman, ft D. Carlini, J. B.Donahue, G. T. Garvey, V. D. Sandberg. W. C.Choi, A. Fazely, ft L Imlay, and W. J. Metcalf

The decays of stopped pions in theLAMPF beam stop present a uniqueopportunity to probe neutrino os-cillations, in the mass region ofbm2 ~ 0.1 eV2, and mixingparameters as low as sin22B ~ 10~\The appearance of vt, will bemeasured with high sensitivity byExp. 645 during the run cycle thatbegins in summer 1986.

Intermediate-energy proton ac-celerators provide neutrino sourcesin the energy range from 10 to50 MeV, which is ideal for oscillationsearches in the mass region8m2 ~ 0.1 eV2. In addition, the avail-able beams are very intense, allowingthe experiments to be sensitive tomixing parameters as low assin220 ~ 10~3. The distance of the detector from the beam stop L and neu-trino energy Ev set a typical oscilla-tion scale of L/Ey, ~ 0.6 m/MeV, avalue intermediate to that obtainedin reactors and high-energy experi-ments.

LAMPF provides a 670-uA protonbeam with a kinetic energy of800 MeV. The beam is absorbed in acopper beam stop, producing on av-erage 0.09 pions for every proton.1

Although both positive and negativepions are produced, 7t~ quickly fallinto atomic orbitals and are absorbedinto the nucleus by strong processes.The n+ come to rest and decay,producing the beam stop neutrinospectra via the decay sequence7t+ —• u+v,,, u+ — e+vev(1. Thesedecays provide a clean point sourceof ve, v^ and v,,.

LAMPF Exp. 645 is located 24 mfrom the beam stop at a polar angle of17° from the main proton beam.The liquid-scintillator detector is thetarget for the inverse beta decay reac-tion vep—* e+n, which, if seen, wouldprovide a signature for the appear-ance of ve. The construction phase ofthe experiment is complete andcalibration and cosmic-ray back-ground studies are currently underway. The first data run is expected tobegin July 1986.

The design and construction of theexperiment are dictated by the ex-pected backgrounds rather than bythe signal of a single isolatedpositron. Because of the long ac-celerator duty cycle (~9%) and be-cause Los Alamos is 2100 m above sealevel, cosmic rays constitute a seriousbackground.

The detector will operate inside atunnel with an overburden of3000 g/cm2, enough passive materialto eliminate the hadronic componentin the cosmic-ray flux (see Fig. 1).The estimated integrated muon fluxinside the tunnel is 8 kHz. In addi-tion, the central detector is coveredby a 4n cylindrical cosmic-ray shield,2

which contains an outer layer ofliquid scintillator (15.2 cm) and aninner layer of lead and iron (12.7 and5.1 cm, respectively). The outer layeris used to veto charged particles. Thepassive layer is designed, inparticular, to eliminate the back-ground of muons stopping outsidethe active layer, where an electronfrom the decay radiates a photon thatcan pass through the scintillator un-detected before it converts inside theshield. To minimize inefficiencies inthe shield, the scintillator fills onlythree optically isolated sections: the

92

RESEARCH


TABLE I Backgrounds Caused by Interactions m the Detector

Targei12C13C27Al

Mass (Tons)

~ 150 150 2

o(1Q-"cm:!Rate/Day in Detector

(Ev > 35 MeV)

cylinder and one end cap, the bot-tom, and the other end cap. The scin-tillator is viewed by 360 photo-multiplier tubes (EMI 48^0-B) toprovide ample redundancy.

The central detector has 40 layers,each one consisting of a scintillatorplane followed by vertical andhorizontal proportional driftchambers (see Fig. 2). The liquidscintillator is contained in horizontalLucite tanks (366 by 30 by 3 cm3) andis viewed at both ends by HamamatsuR878 phototubes. Particles lose 75%of their energy in the scintillator; therest is deposited in the Lucite anddrift-tube walls. The drift-chamberplanes consist of 45 wires assembled8.1 cm apart. Drift-time and pulse-height information are recorded for

1 5<5<5

<0 01<005<0 03

every wire. Nuclei with looselybound neutrons—for example, 27Aland l3C—provide a target for ve interactions and are a source of back-ground because we are not able todistinguish between electrons andpositrons (see Table 1). Thus, thedrift tubes are constructed oflaminated Kraft paper, with only a 25-u.m aluminum inner layer to shapethe electric field.3 The detectorweight is 20 metric tons, of which2.3 tons is hydrogen.

We must be able to distinguishprotons from electrons with high effi-ciency in order to eliminate knock-on protons produced in fast-neutroninteractions. The granularity of thedetector permits such identification

Beam

55m-

AssemblyBuilding - ,

Water Plug [Porch for

Electronics

Rails

(b)

5.1-cm Ironand 12.7-cmLead

FIGURE 1. Cosmic-ray shielding lor theneutrino tunnel (a) side view and (b) frontview. The shielding includes3000 g /cm 2 of overburden, an activecharged-particle veto, and an inner layerof lead and iron

-ff ,

Liquid Scintillator(366 by 30 by 3 cm3)

Vertical ^and

HorizontalDrift Tubes i

(8.1-cm Spacing)

5mg/cm 2

Gd2O3/Sheet

HamamatsuR878

Phototube

7 m

FIGURE 2 Neutrino detector sandwich (elevated view), consisting of 40 scintillatorand drift-chamber planes.

93


102

10

1

10"''

; OscillationSensitivity

i i J

10"4 10~3 10~2 10 " '

Am2(eV2)vssin2(29!

FIGURE 3 Expected sensitivity oiExp 645 to neutrino oscillations Thedashed curve assumes the experiment istree ot background, the lull curve as-sumes a background rate otO Ievents/day, and the dotted curve showscurrent oscillation limits

to be made by comparing the particlerange with the energy loss measuredin the scintillator. An additionalselection can be made based on thedE/dx measurement in a single ac:r;tillator plane. Using these criteria, wehave rejected protons by a factor of3 X 10"* in a prototype detectorstudied in the LAMPF test beam chan-nel. Given the present estimates ofneutron backgrounds (~ 1000/day)in our detector, this rejection is ade-quate to eliminate knock-on protonswith kinetic energies greater than100 MeV.

The signals from the detector andthe shield are digitized with Hashanalog-to-digital converters (ADCs)and stored in cyclic memories con-taining 150 (is of data. After thepositron trigger is flagged by hits inthree consecutive planes, data con-tinue to be read into the memoriesfor 100 u.s, so that when the data areeventually transferred to the com-puter, only 50 \is of information arerecorded before the event trigger.

The history is used to tag any signalsthat might be associated with the trig-ger—for example, a stopping muon.The data recorded after the triggert:s;p iucTitny' liiv; neutron u.ai wouldbe present if the evei.i were in fact av8 interaction.

Mylar sheets painted with naturalGd2O3 are located between all scin-tillator planes. Neutrons from the in-teraction may thermalize in the scin-tillator and capture on gadolinium,which deexcites by emitting4.5 gamma rays on the average. Thedetection of these gammas (totalenergy is 7.9 MeV) provides a neu-tron signature. The detection effi-ciency of the neutrons is expected tobe about 25%, but depends on re-quirements imposed on the detec-tion of the resulting gammas.

In Fig. 3 we show the expectedsensitivity of Exp. 645 to neutrino os-cillations. The vEp-interaction crosssection4 is 11 X lO-41 cm2. Assuminga positron detection efficiency of50%, the event rate for maximum os-cillation is 47 events/day. We hope tokeep background rates, which limitthe sensitivity of the experiment, toless than 0.1 events/day. For com-parison, the best published limits arealso shown in the figure.5

94


References

1. R. C. Allen et al., Physical Review Letters 55,2401 (1985); and H. H. Chenet al., Nuclear Instruments & Methods 160, 393 (1979).

2. S.J. Freedmanetal., Nuclear Instruments & Methods215,71 (1983).

3. J. Fitch etal., Nuclear Instruments & Methods 226,373 (1984).

4. S. E. Willis et al., Physical Review Letters 44,522 (1980); and S. E. Willis etal., Physical Review Letters 45,1370 (1980).

5. L. A. Anrens et al., Physical Review D 31, 2732 (1985); F. Bergsma ec al.,Physics Letters 142,103 (1984); and G. N. Taylor et al., Physical Review D28,2705(1983).

95

RESEARCH


EXPERIMENTS309, 750, 859,and 957 — P3

A Dependence of Inclusive PlonDouble Charge Exchange

Los Alamos, MIT. Univ of Wyoming,Univ. ol New Mexico, Tel Aviv Univ ,Colorado College

Spokespersons: P. A. M. Gram (Los Alamos), J. L.Matthews (M1V, and G. A. Rebka. Jr. (Univ. ofWyoming)

Participants: C. A. Bordner, D. A. Clark, S.Hoibraten, E. ft Kinney, D. W. MacArthur, P.Mansky, £. Piasetzky, D. A. Roberts, C. R.Schermer, T. Soos, S. A. Wood, and H.-J.Ziock

TABLE I

"iuc'eus4He

1 5 Q

4 0Ca

'03Rh2O8pD

Total inclusive Double-Charge-Exchange Cross Sec-tions for the A(n+,K~lion in Severaland 240 MeV

180 Me-/

0 5 4 + 0 05

1 92 ± 0 23 30 ± 0 445 -'2 ± 0 74

16 2 ± 2 033 7 ± 4 0

") *Nuclei at

]

49

59

27

73

Reac-130

240 MeV

09347947

3824

± 0± 0± 0± 0± 0± 3± 7

1

5354q

00

The strength of the elementarypionnucleon interaction suggests,and analysis of pion-nucleus reac-tions confirms, that multiple scatter-ing plays an important, if often in-direct, role in all pion-nucleus reac-tions.1 Inclusive pion double chargeexchange (DCX) is of special inter-est because charge conservationalone demands that at least twonucleons within a nucleus explicitlyparticipate in the reaction. Thus DCXprovides a way directly to study mul-tiple scattering in pion-nucleus reac-tions. At present there is no adequatetheoretical description of multiplescattering of strongly interactingparticles in nuclei. To promote theconstruction of such a theory it isuseful to establish the systematics ofthe DCX reaction.2

Our experimental program, startedin 1981, has produced accurate, sys-tematic measurements of the doublydifferential cross sections for in-clusive DCX, establishing its de-pendence on the energy and chargeof the incoming pion, the outgoingpion energy, the angle of observa-tion, and the target nucleus in ninenuclei3'6 ranging in atomic weightfrom 4 to 208. Important informationabout the reaction mechanism is con-tained in the dependence of the DCXcross section on the number of neu-trons r>nd protons in the targetnucleus. We present here a sample ofour observations of this dependencein the total-reaction cross sections forboth the A(n+.K~) and the A(n~,n+)reactions at two incident pionenergies.

In a simple classical picture theDCX reaction proceeds as two suc-cessive quasi-free single-charge-ex-change (SCX) scatterings. In the(7t+,n~) reaction the SCX reactionstake place only on the neutrons,whereas in the (Jt~,7t+) reaction theSCX reactions take place only on theprotons. In the limit of a weak pion-nucleon interaction, the probabilityof the first SCX scattering would thusbe proportional to N (the number ofneutrons) or Z (the number ofprotons), depending on the charge ofthe incoming pion. The probabilityof the second scattering would beproportional to N— lo r to Z— 1.Therefore, we might expect the crosssection for DCX to be proportional toQ(Q— 1), where Q is the number ofnucleons of the appropriate type.This picture also suggests that a com-parison of (rt+,7O and (K~,K+) on agiven nucleus may lead to informa-tion on the relative neutron andproton structure of the nucleus.

In these experiments the doublydifferential cross section G( Tfi) wasmeasured for each target and inci-dent beam at several angles, withcomplete coverage of the outgoingpion energy spectrum from 10 MeVup to the kinematic cutoff for in-clusive DCX. Absolute cross sectionswere obtained by normalization withrespect to np scattering. The a(7",0)was integrated over outgoing energyat each angle to yield singly differen-tial cross sections c(9). These werefitted by sums of Legendrepolynomials. Total-reaction crosssections were obtained by integratingthe fitted functions over angle. Thecross sections, given in Tables I and

96

BESEABCH


II, are all preliminary results exceptthose for l6O and40Ca.

Figure 1 presents the variation ofthe reaction cross section with A forthe (7t+,jT) reaction at 180 and240 MeV. The monotonic rise of thecross section according to a powerlaw in A is not unexpected. Only thecross section for 9Be, which has an

100

10

Ie

1

1

r »

: i

in

i

]

m l

10

i

r*.rr-

«

I

A

)X

ii

Ml

100

I

i

Hill

1000

FIGURE 1 Total inclusive DCX crosssections for the A{ j t + . i r ) reaction at 180and 240 MeV as a lunation of A (0,240 MeV)and V(180 MeV)

A possible explanation of this ef-fect is that the large neutron excess inheavy nuclei shields the protons fromthe incoming negative pions. At theA-resonance energy, negative pionsinteract strongly with neutrons andrelatively weakly with protons, but itis the protons on which DCX takesplace. Moreover, there is theoretical

10

1

*

i

10

Mr

i

i

i

A

X

1

i

100

f

-

-

1000

FIGURE 2 Total inclusive DCX crosssections lor the ,4(jt~,;i+) reaction at 180and 240 MeV as a lunction ot A.

TABLE II, Total Inclusive Double-Charge-Exchange Cross Sec-tions lor the /A(JI~,JI+ )X Reac-tion in Several Nuclei at 180and 240 MeV

Nucleus

"He9Be

16Q

4 0 Ca103R h

20Bpb

3

180 MeV

.43 ±6,69 ±55

43 ±.48 ±

0.440 8 51.01 0

1

25

101112

240 MeV

26.23.32.22.96

±++±++

0,160 30.540.951.02,0

extra neutron, deviates significantly,lying about a factor of 2 above thegeneral trend. The surprising result isshown in Fig. 2. The cross section forthe (7r"",it+) reaction rises approx-imately parallel to that for the (K+,TC)

reaction up to about A = 40, where itbecomes constant and remains so upto A = 208, despite the fact that leadhas over 4 times as many protons ascalcium.

reason to believe that in heavy nucleia fraction of the neutron distributionlies outside the proton distribution.Therefore, DCX is inhibited by com-peting reactions that occur on theneutrons. Naturally, neutrons andprotons exchange roles for positiveincoming pions, but there are noheavy proton-rich nuclei, so the crosssection does not saturate at somevalue of A Observation of DCX in3He, planned for the future, will bevery interesting.

97

RESEARCH


T, = 180 MeV

o(jt+,jt")Q

X(n",jt+)Q

0.001

Igo

1

01

0.01

\\

• (b)• • • •

C

\

• • • • • ' • * "

24 J MeV

<(7t-,7r+)Q = Z ;

(A-Q)- " 1 :

\i10 100

A - Q

FIGURE 3. Total inclusive DCX cross sections at (a) 180 MeV and (b) 240 MeV,divided by 0 ( 0 — 1) and plotted against [A — Q), where O = N for (7t+,7t~) and Q = Zfor(rc~,7t+) The lines correspond to fits of the form Q{Q— 1)/[A — Q)D, For both lines,p = 1.4.

These qualitative ideas suggest anempirical parameterization of DCXtotal cross sections by the simplef o r m a - Q(Q- D / G 4 - Q)p,where A— Q represents the numberof spectator nucleons on which com-peting reactions can occur. Figure 3displays the cross sections for both(jt+,;t~) rnd (JI~,JI+) plotted accordingto this simple organizing principlefor 180 and 240 MeV. The verticalaxisiso/QCg— 1) and the horizon-tal axis is (A — Q). In these graphs,cross sections for both charges of in-cident pion occur at the same valuesof (A — Q) for N = Z nuclei, but atdifferent values of (A — Q) for N*£ Z

nuclei. Nevertheless, all the crosssections at a particular energy,including those for 'Be, lie accep-tably close to a straight line, whichhas a slope of—1.4 for both energies.Thus for the N= Z nuclei thisparameterization implies thata ~ A06, rather close to the AVi de-pendence characteristic of reactionsthat occur on the surface of thenucleus.

We are a long way from com-prehension of the reactionmechanisms at work in DCX, but thesuccess of this simple classical pic-ture suggests that sequential SCXscattering operating in competitionwith the much more probable quasi-free scattering process is a useful ideawith which to begin.

98


References

1. M. Baumgartneretal., Physics Letters 1128,35 (1982).

2. J. L. Matthews, in "Proceedings of the LAMPF Workshop on Pion DoubleCharge Exchange," Los Alamos National Laboratory report LA-1O55OC(September 1985).

3. S. A. Wood, Los Alamos National Laboratoryreport LA-9932-T (1984).

4. S. A. Wood et al., Physical Review Letters 54,635 (1985).

5. E. R. Kinney et al., Bulletin of the American Physical Society 29,1051(1984).

6. P. A. M. Gram et al., Bulletin of the American Physical Society 30,783(1985).

99


EXPERIMENT 804 — P3-EastMeasurement of the AnalyzingPower In i rp — yn and irp — n'nUsing a Transversely PolarizedTarget

UCLA George Washington UnivCdthonc Univ oi America, AbileneChristian Univ , Los Alamos

Spokesman: 8. M. K. Nelkens (UCLA)

The experimental setup is shownin Fig. 1. The major components aretwo sets of 15 neutron detectors, twosets of 15 gamma detectors, and theLos Alamos P-Division polarizedproton target. The incident beam wascentered on the target using twosteering magnets in the beam line5 m upstream of the target. Thesemagnets were used to correct for thebending of the beam at the target bythe "C" magnet of the polarizedtarget. A pair of thin scintillationcounters 5, and 52, located 60 cmupstream of the target, defined thebeam. The beam flux was typically0.9 X 106 iC/s on a 2-cm-diam spot on

FIGURE 1 Layout of the experimental setup The beam was centered on the targetwith the help ol x and v-steenng magnets Si and S2 are the beam-defininq scintillationcounters, Ni and /Vgare two sets of noutron detectors, and GA and Geare iwo sets olcorresponding gamma detectors WV4and VNB are charged-particle veto counters infront ol the neutron detectors, and VGA and VGB are veto counters lor the gammadetectors

the target. The central momenta andrespective momentum bites of theincident beam were 427 ± 2,471 ± 2,547 ± 4, and 625 ± 6 MeV/c.

The target consisted of 1-mm-diamethylene glycol beads contained in atruncated sphere 4.6 cm in diameterand 2.8 cm high. The target polariza-tion, typically 80%, was measuredwith a nuclear magnetic resonance(NMR) system.

The final-state neutron and gammawere detected in coincidence. Thegamma detector consisted of 15counters arranged in a 5 (ver-tical) X 3 (horizontal) rectangulararray. Each counter was a 15- by 15-by 25-cm-deep lead-glass block op-tically isolated from its neighborsand viewed by a 12.7cm AmperexXP2941 photomultipliertube. Theneutron detector also consisted of 15counters, each a cylindrical plasticscintillator 7.6 cm in diameter and45.7 cm long, viewed by an RCA 8575photomultiplier tube.

An important consideration in de-signing the experiment was the cleanseparation between the REX(radiative-exchange), n~p—* yn, andthe CEX (charge-exchange),n~p—• n°n, events. Experimentally,the REX and CEX events have ident-ical neutral particles in their finalstates, but the CEX reaction has across section very much larger thanthat for REX. The gammas from theREX reaction are kinematically re-stricted to a small area on the gammadetector. The n° yields two back-to-back gammas in the rc° rest frame thatare folded forward in the laboratoryframe by the Lorentz transformationand that illuminate the entire areacovered by the gamma detector.

100

RESEARCH


The neutron counters were arranged such that each counter wasmatched to a unique gamma counter,as dictated by the kinematics of thetwo-body final state of the REX reac-tion. Figure 2 shows the front faces ofa gamma detector and the matchedneutron counter array. The radial dis-tances of the detectors, between 2and 3 m, were chosen on the basis ofa Monte Carlo study in which weoptimized the REX-signal-to-CEX-background ratio within amatched neutron-counter-gamma counter pair. Radial distancesof both the neutron and gamma de-tectors were changed for differentscattering angles and incident pionmomenta, and the neutron counterswere also rearranged to preseive theone-to-one neutron-counter-to-gamma-counter matching.

Chargedparticle veto counters, VNand VG, were in front of the neutronand gamma detectors. There weretwo pairs of neutron-gamma detect-ors, each pair with a completelyseparate set of electronics. This ar-rangement allowed the measurementof two angular intervals simultane-ously. For each event we recordedthe pulse heights and time of flightsfrom all neutron and gamma countersand the time of 5,, S2, and the 200-MHz rf pulse on which the ac-celerator was timed. All times weremeasured relative to the gammacounter that triggered the event. Therf timing signal was used to correctfor small timing differences causedby different gamma counters startingan event, and to remove any timing

jitter caused by different gamma interaction points and the transmissionof light within a gamma counter.

In the data analysis the neutrontime of flight and the gamma pulseheight were very useful in eliminat-ing a large fraction of the backgroundevents from the 90%-by weightnonhydrogenic parts of the polarizedtarget. The neutron time of flightcould not be used to completelyseparate the REX and CEX eventsexcept at low energies or at very for-ward gamma angles; a fraction of theCEX events was removed by the useof a narrow window on the neutrontime of flight while retaining most of

DETECTOR

5

4

3

2

1

10

9

8

7

6

15

14

13

12

11

NEUTRONDETECTOR

Polarized ProtonTarget n

Beam intopage

15 cm

00©

7 6 cm diameter45 cm long

— 15 25 4 cm deepcm

FIGURE 2 The neutron counters and gamma counters arranged m one-to-onematching prescribed by REX kinematics

101

RESEARCH


15

£ 10

o

Eo

the REX events. The major challengeof the data analysis was the cleanseparation between the small REXevents and the preponderant CEXevents. The key to handling the prob-lem was to exploit as much aspossible the two-body character ofthe REX compared with that of thethree-body CEX reaction.

After applying the neutron time-of-flight and gamma pulse-height cuts,we constructed a scatter plot display-ing the event distribution from allneutron-counter-gamma-countercombinations. Using the one-to-oneneutron-counter-to-gamma-countermatching prescribed by the REXkinematics, the counters werenumbered such that neutron

m u

0Neutron counter #

FiGUPE 1 " : A'O-dimens;onal neutron-counter-gamma-counter event distributionThe diagonal elements ol this 2D histogram are events Irom the matched neutron-counter—gamma-counter pairs The circled elements are events Irom neutron- andneighboring gamma-counter pairs £ slight REX enhancement can be seen inneighboring elements

counter 1 corresponded with gammacounter 1, etc. (see Fig. 2). Figure 3displays a two-dimensional histo-gram of the number of events in eachneutron-counter-gamma-countercombination; the REX events ideallylie only on the diagonal whereas theCEX events are distributed over theentire histogram. Because the neu-tron-counter-gamma-countermatching was not perfect, there was aslight REX enhancement in the adja-cent counters.

The analyzing power is given bythe expression

1AN=-

Nu - Nd

P, Nu+ Nd-2B '

where P, is the known targetpolarization, Nu is the normalizedyield of evenis that passed the gammapulse-height and neutron time-of-flight cuts of the spin-up target, Nd issimilar for the spin-down target, andB is the normalized backgroundyield.

The background yields weremeasured in separate runs in whichthe target material was replaced byTeflon (C2F4) beads. The number ofevents is normalized by the beamflux. Only the events that lie on thediagonal of the ID histogram areconsidered REX candidates. The dif-ficult problem in calculating the REXasymmetry is the reliable subtractionof the CEX contamination among theREX candidates to yield the true REXevents. A 2D histogram of the CEXdistribution was produced using aMonte Carlo code. From this Monte

102

Carlo CEX distribution, the numberof CEX background events in thediagonal elements of the 2D histo-gram was calculated from thenumbers of CEX events from the non-diagonal and the nonadjacent ele-ments. Typically, the background was30%, of which 90";, uf the backgroundwas CEX events and the rest camefrom the nonhydrogenic material inthe target.

Some preliminary results of theanalyzing power AN in the REX reac-tion at 427,471, 547, 586, and625 MeV/c are shewn in Figs. 4-6.

The solid lines are the predictionsfrom the most recent energydependent partial wave analysis of singlepion photoproduction by Arai andFujii.1 The agreement is poor, whichleads us 10 question their value forthe radiative decay amplitude of theRoper resonance, A"/z = 23 ± 9 X10~3 Ge\r~1/2. Comparison is alsomadf with the prediction of a 197"7

partial-wave analysis (PWA) byNoelle2; the agreement with our datais good. The only other existingmeasurements of the asymmetry are afew points at 427 MeV/t by a SINgroup.3 Within their sizable error ofabout 0.2, there is good agreementwith our results, as shown in Fig. 5.

As a consequence of time-reversalinvariance, AN must be the same insign and magnitude as the recoilproton polarization P measured in K~photonroduction from a neutrontarget. Some results obtained with adeuterium target4 6 at 90°, shown in


0.8

0.1'N

0

-0.4

0.8

-0 .4 -

(a) 47IMeV/cif'pl—yn

Ami, Fu,ii

Noelle

^ This eiperimeflt

—i 1 1 1 1—

(c) 5B6MeV/c

| 547MeV/c

(d) 62SMeV/c

08 0.4 0 - 0 4 -0.8

cos Br

0.8 0.4 0 "0.4

cos Br

-08

FIGURE 4 Asymmetry parameter Admeasured in n p —• yn, using a transversely

polarized target The incident pion momenta are (a) 4 7 1 , (b) 547 , (c) 586, and

(d) 625 MeV/ c The solid lines are the predictions Irom the energy-dependent partial-

wave analysis ol single-pion production by Arai and Fujii (Ret 1) The dashed hnes in

(a) and(c) are the predictions tw Noelle (Ret 2) ot (a) p » = 471 MeV/ L and

(c) pK= 575 MeV/ c The statistical and systematic uncertainties were summed m

quadrature

0.8-

-0.4

127MeV/cF " p t — yn

Arai, Fuji!

\ Alder et al.

f This experiment

0.8 0.4 0

COS fly

-0.4 0.8

FIGURES Asymmetry parameter /^measured in K p—yn Results ol the presentexperiment are compared with the data o(Adleret al (Ref 3)at427MeV/c

103

RESEARCH


300

pT(MeV/c)

500 700

Aroi, Fu|ii

Noelle§ Beneveniano el al. ( P | -$ Kenemuih, Stein (P)i Takeda el ol. (P) "

This eipenmenl (&N)

500 700Ey(MeV)

900

FIGURE 6 The asymmetry parameter obtained in AN in this experiment compared•Mth !he recoil proton polarization data p measured man photoproduction reaction at90 using a deuterium target by Beneventano et al (Rel 4) ,J Kennemuth and P CStem (Ret 5),anc)H Tacedaetal (Rel 6)

Charge Exchange471 MeV/cKarlsruhe-HelsinkiVPI (1984)

-1.0

FIGURE 7 Asymmetry parameter/Admeasured in jt p —• n°n using a transverselypolarized target The solid curve is the prediction by the Karlsruhe-Helsinke (K-H)group (Rel 7] and the dotted curve is Ihe prediction by VPI (Ret 9)

Fig. 6, are compared with our work.Because there is currently no reasonto doubt the applicability of time-reversal invariance in this process,we conclude from the poor agree-ment between our data and that ofthe inverse reaction measured with adeuterium target that the deuteriumcorrections are not well understood.Hence the radiative decay amplitudeof neutral resonances based on deu-terium-target data should be re-evaluated.

Easily obtainable and very valuableby-products of our REX experimentarj; some accurate data on the analyz-ing power of the CEX reaction. Thesedata have become very important forchecking the correctness of thedouble Roper resonance pole, whichis the outcome of the 1984 VirginiaPolytechnic Institute and State Uni-versity (VPI) partial-wave analysis.Our preliminary CEX data atp^ = 471and 625 MeV/c are shown in Figs. 7and 8 together with the predictionsof the partial-wave analyses by theKarlsruhe-Helsinki (K-H), Carnegie-Mellon University/LawrenceBerkeley Laboratory (CMU-LBL), andVPI groups (Refs. 7,8, and 9, respec-tively). The predictions of the partial-wave analyses are in good agreementwith our AN data at 471 MeV/c. At625 MeV/c the predictions of variouspartial-wave analyses diverge atbackward angles and our AN dataagree best with the 1984 VPI solu-tion. This is very interesting becausethe VPI solution shows the Pu wavehaving two nearby poles in the com-plexplaneat (1359,-100/) and(1410,-80/) MeV/c.

104


1.0

0.5

-0.5

Charge Exchange T T " + p t - * 7 T ° + n -6£5 MeV/c

' Karlsruhe - Helsinki1 CMU-LBL '_

VPI (1984)- § This Experiment

.0 0.0 -1.0

COS dwa

FiGURb 8 Asymmetry parameter AN measured mit p - * jt°n The solid curve is theDrediction by K H(Ret 7), the dashed curve, CMU-LBL (Ref 8), and thedotted curve,VPi |Ret 9)

References

1. I. Arai and H. Fujii, Nuclear Physics B194, 251 (1982).

2. P. Noelle, Ph.D. thesis, University of Bonn report Bonn-IR-75-20 (1977);and P. Moelle, Progress ofTheoretical Physics 60, 778 (1978).

3. J. C. Adleret al., Physical Review D 27,1040 (1983).

4. M. Beneventano et al., LetterealNuovoCimento 3, 840 (1970).

5. J. R. Kennemuth and P. C. Stein, Physical Review 129, 2259 (1963).

6. H. Takeda et al., Nit clear Physics B168,17 (1980).

7. G. Hohleret al., "Handbook of Pion-Nucleon Scattering," Physics Data12-1(1979).

8. R. E. Cutkosky et al., Physical Review D 20, 2804 and 2839 (1979).

9. R. Arndt et al., Physical Review D 32,1085 (1985).

105

RESEARCH


EXPERIMENT 827 — P 3

Study of Isobarlc-Analog-StateTransitions with Plon Single ChargeExchange In the 300- to 500-MeVRegion

. ns -Marnos. Tel A;i\ Urv. ' Hah Stateunr. . Arizona State Univ , univ ol

, SiN

Spokesmen: J. Alster (Tel Aviv Univ.), H. W. Baerand E. Piasetzky (Los Alamos), and U.Sennhauser (SIN)

This was the first experimentperformed with the TI" spectrometermounted in the P3 channel. Thepurpose of the experiment is to ex-tend the empirical systematics ofisobaric-analog-state (IAS) differen-tial cross sections to energies abovetheA(P33) resonance. Questions ofparticular interest are whether the 0°cross sections are well representedby the form g(N — Z)A~a and, if so,whether the values of g and a con-tinue the trends observed at energiesbetween 100 and 300 MeV. Thesetrends show a to be a decreasingfunction of energy, going from 1.40 at100 MeV to 1.10 at 295 MeV. Theenergy dependence of g follows ap-proximately the shape of the freecross section da/d£l(n~p —»7t"«) at0°. From the preliminary analysis ofthe data, given below, we see largesurprises relative to expectationsbased on these trends.

Another goal of this experiment isto provide a test of pion-nucleus scat-tering theory at an energy where thistheory is expected to work best. Atenergies around 500 MeV the reac-tion mechanism is generally expected to be simplified considerablybecause of the lesser role of isolatedresonances in the 7C./V system, theweaker optical potential, and thesmaller pion de Broglie wavelength.Thus the data should give a less-am-biguous evaluation of the theory thanat lower energies.

In a 22-day data run in August-September 1985, we measured the(7i+,7t°) forward-angle differentialcross sections (0 to 8°) at four ener-gies on various targets (Table 1).

The resolution in the 7C° spectrameasured at P3 was not as good as thatin the LEP measurements because ofthe poorer momentum analysis of theP3 beam. The smallest value al'Ap/pwe were able to obtain was approx-imately 1% (even if the momentumslits were set for smaller values). Thiscorresponds to AE= 4 MeV at 300-MeV incident energy andAE= 6.6 MeV at 550 MeV. In addi-tion, it was necessary to put thickdegraders into the beam (11.5-cmgraphite at 550 MeV) to reduce theproton contamination; this degraderfurther broadened the incident pionenergy distribution. The final energyresolutions we obtained in the 7i"spectra were approximately 8 MeV at425 MeV and 11 MeV at 500 MeV.

The K° spectrometer was mountedin its two-post configuration to allowfor large target-to-detector distances(/?). All data were taken withR= 2.0 m and with a nominal setupangle of 0°. This gave a finite accep-tance for 7i° scattering angles in therange from 0 to 10°. In the off-lineanalysis the data were binned intothree groups according to measuredscattering angles.

The incident n flux was measuredusing the scintillator activation tech-

TABLE 1 Measurements ol (TC+

TjMeV)

300425500550

,JU°) Forward-Angle

Targets

TU, l dC>"Al '7L,.'4C,27AI7Li.MC

Dillerential

6 0Ni 9 0 7 ,6 0Ni

Cross Sections

i ?o G n 2os p b

106


nique. Because the protons in thebeam also induce "C activity, a coi-rection had to be applied based onthe measured proton contaminationsand known proton activation crosssections. The proton/pion ratios ateach energy were measured using asampling-grid scintillator. Typicalbeam conditions at which data weretaken are given in Table II.

Figure 1 shows the TI0 spectra atTK = 425 MeV at the most-forwardscattering angle for targets from 7Li to208Pb. The IAS peaks can be well identified at the expected energies. Themeasurement for the Jt~p—• Jt°« reac-tion, also shown in Fig. 1, wasperformed with a CH2 target. Thecarbon contribution was subtractedout using a measured carbon spec-trum. The solid curve represents aMonte Carlo calculation for the lineshape and gives a good description ofthe data. The curves shown with the(jt+,7t°) data represent fits done with asingle peak plus a polynomial function for the background. The peak isconstrained by the energetic positionof the IAS and the Monte Carlo lineshape. We see that this model gives afair representation of the data.

At 500 MeV we took data only on7Li,'-'C,27Al,and60Ni because of thelimited run time. The most-forward-angle spectra are shown in Fig. 2.Again, the IAS is clearly discernibleat the expected energies, and one cansee that the line shapes calculated byMonte Carlo simulation describe thedata quite well.

TABLE II

7", (MeV)

300425500550

Typical Beam Conditions

n+Flux (s"')

1 X 107

5 X iO6

2 5 X 106

8 X 10"

During Data Taking for Exp.

Ap/p(* )

020 20 405

827

Proton/Pion Flux

~00 020 16A 0

!

360 380 400 420

ir° Kinetic Energy (MeV)

FIGURE 1 Spectra lor the (n+,n°) reaction at 425 MeV for various nuclear targetsThese spectra were measured at the P3 channel with the LAMPF jt° spectrometer Tpeaks occur at the expected energies for the IAS transitions.

107

RESEARCHNuclear and Panicle Ph-,3ics

400

200

'Li

400

200

460 480 500 520 540

TT° Kinetic Energy (MeV)

FIGURE 2 Soectialor the iJi+,7t°) reac1 • • it 500 MeV lor various nuclear targetsThe peaks occur at the expected enerq.c TH the IAS transitions

In Fig. 3 we show the data on 60Niat 425 MeV for three values of scatter-ing angle. These show the IAS to be avery sharp forward-angle feature. At7° the IAS is hardly visible in thespectrum. We expect these angulardistributions to follow zj\{qR)shape. The first zero of a Bessel func-tion of order 0 is 2.405. For an inter-

action radius R = 1.25 41/3andabeam energy of 425 MeV, this wouldgive a first minimum for 60Ni at 10°,which is consistent with the data. Wewill analyze the data to obtain boththe 0° cross sections and the rate offalloffversus^CorG2).

In Fig. 4 we give preliminary -i°cross sections for 7Li and HC at 425and 500 MeV. Also shown are pub-lished cross sections at lowerenergies. The factor of 2 rise in crosssection between 300 and 425 MeV issurprising. Certainly this is not a fea-ture that exists in the elementaryri~p—- n°n cross section. Its energydependence (Fig. 4) is such that thecross section drops by approximately25% between 300 and 500 MeV. Itwill be interesting to understand theorigin of the sharp rise in the nuclearcross sections.

The near equality of the 7Li and 14Ccross sections between 230 and500 MeV is consistent with an(N— Z)/A dependence in the crosssections. In a plane-wave model oneexpects an (N— Z) dependence forthe 0° cross sections. In a strong-absorption model one expects an(/V- Z)/Ai/i dependence.

When we complete the data analy-sis, the excitation functions between165 and 425 MeV will be known for7Li,14C)

27Al,60Ni,90Zr,120Sn,and2o8Pb.For the lighter nuclei, 7Li to f0Ni, theexcitation functions will be de-termined up to 500 MeV. For 7Li andl4C they will be determined from 20to 550 MeV.

108

RESEARCH


!PU

bM

360 380 400 420 440

7T° Kinetic Energy (MeV)

FIGURE 4. Excitation function of the 0°IAS cross sections for 7Li and 14C. Thenew (preliminary) data at 425 and500 MeV show that the cross sectionrises sharply above 300 MeV. The freecross section da/d£2cm(n~p — n°n)versus Tn[\ab) is shown as a solid line.Between 300 and 500 MeV it is a gradu-ally decreasing function of energy, insharp contrast to the thape of the excita-tion lunctions for the nuclear targets.

FIGURE- 3 Spectra for the NifTt+.n3) reaction ai 42a MeV at three forward angles.The IAS transition has a sharp forward-peaked angular distribution.

109

RESEARCHNucleai and Particle Physics

EXPERIMENT 852 — P 3 •

Measurements of (nr,n) Reactionson Nuclear Targets to Study theProduction and interaction ofil Mesons with Nuclei

Los Alamos, Univ ot Virginia

Spokesman: J. C. Peng (Los Alamos)

Participants: J. E. Simmons, M. J. Leitch, J.Kapustinsky, J. M. Moss. C. Lee, S. Tang, J.C. Peng, J. D. Bowman, F. Irom, Z. F. Wong, T.K. Li, C. Smith, and R. ft. Whitney

Discussion on the physics motiva-tions of Exp. 852 and results from atest run appeared in the 1984 Pro-gress Report.

This experiment has receivedbeam time in 1985 for the followingmeasurements:

1. the 3He(7t~,/)T| reaction. Tritonsare detected with the large-areu-re spectrometer (LAS) atforward angles (5 ° < 9lab < 15")with 620- and 680-MeV/c n~beam.

2. the 3He(jT,Ti)f reaction. TheLAMPF 7t° spectrometer and theUniversity of Virginia 3He targethave been used to measure thisreaction through the detectionof T) —• 2y decays. Cross sec-tions at forward angles (0 °<9 l a b< 30°) have been

measured at six beam momenta(590MeV/c < / > ( O <700MeV/c).

3. the (rt+,Ti) reaction on 7Li,9Be,and 13C. Energy resolution inthese measurements is op-timized to examine whetherisobaric-analog states (IASs)can be strongly excited in the(n+,T|) reaction.

4. the inclusive (7t+,r|) reaction on3He,4He,7Li,9Be,12C,27Al,40Ca,120Sn, and 208Pb at 620,650, and680 MeV/c.

The data are currently beinganalyzed. Some of the preliminaryresults are presented in this report.

Figure 1 shows the triton spectrumobtained in the 3He(7i~,f) measure-ment using the LAS. A peak is ob-served in the triton spectrum at a

\ t ) , 680MeV/t,35

30 -

oCM

w"c73O

o

25

20

15

10

5

1 • ' I f i ( I ( i I r3He(Tr-,i)i7

Rt I I 1 I I 1 1 [ I I

XLi i i I i i i i

500 700 900Triton Momentum (MeV/c)

MOO

FIGURE 1. Energy spectrum of the 3He(7i ,f) reaction. The arrow indicates the ex-pected location of the 3He(7t~,f )T| peak.

110

RESEARCH


CH2(TT-,77) 705 MeV/c

lid,, i200 400 600

Mass (MeV)800

FIGURE 2 Invariant mass plot tor the two photons detected in the TI + CH2 reactiorusing thp LAMPF n° spectrometer

location expected for the 3He(7t ,/)TIbinary reaction. Note that this peakstands out rather clearly above someother possible backgrounds, such asthe 3He(7t~,?)7t+7i~Jt° reaction thatcontributes a continuum triton back-ground. Preliminaryanalysisgivesacross section of 1 fib/sr for the3He(7t~,J)T) reaction. Because tritonsare detected at very forward angles,the measured cross section cor-responds to the backward angle inthe 3He(7T,T|) t reaction. This is thefirst time that a discrete final state hasbeen observed in the (7t,rj) reactionon nuclear targets.

The LAMPF rc° spectrometer,moved to the P3-East area from theLEP channel during 1985, was usedfor the (JI,T|) measurements. Figure 2shows that the t| mesons are clearlyidentified from the invariant massplot. The T|-energy spectra are shownin Fig. 3 for the 3He(7C~,r|) reaction atthree pion beam momenta. At680 MeV, which is near the freep(7t~,T|) n threshold, the 3He(7C~,T|) /reaction appears as a shoulder of thequasi-free 3He(7C~,T|) reaction. As thebeam momentum is lowered to

111

RESEARCH


40

30

20

10

0

80

I 60

OJ

£ 40Coo

20

0

30

25

20

15

10

5

0

sHe Reaction

680 MeV/c -

620 MeV/c

590 MeV/c :

50 I00 I50

17 Energy (MeV)200

620 MeV/c, the separation betweenthe ground-state transition and thequasi-free continuum improvesgreatly. At 590-MeV/c pion momen-tum, which is just above the absolutethreshold of the 3He(7t~,Ti) t reactionand below the threshold of any other3He(jt~,r|) channels, the 3He(jt~,Ti) treaction is unambiguously detected.We expect to study the mechanism ofthe (7i,T|) reaction and the T|-nucleusinteraction through the energy de-pendence and angular distribution ofthis reaction. It is intriguing that thesubthreshold (n:,T|) reaction has ap-preciable cross sections.

Preliminary results also show thatIASs are excited in the (7t+,Ti) reac-tion on7Li, 9Be, and 13C. This issurprising because the momentumtransfer in the (7t,T|) reaction, unlikethe situation in the (7t,7t°) reaction, israther unfavorable for exciting theIASs. We note that the (i^ft) reactioncan be considered as an unconventional charge-exchange reaction. Theconventional charge-exchange reactions, such as (p,n), (3He,/), and(T^,n°), involve a pair of particlesbelonging to the same isospin multi-plets. In contrast, the (7 ,11) reactioninvolves a pair of mesons belongingtc different isospin multiplets. Weexpect that the (7t,r|) reaction couldalso shed new light on the mecha-nism of charge-exchange reactions.

FIGURE 3 The T|-energy spectra measured in the 3He(7t~,r|) reaction with threedifferent i t " momenta The arrows indicate the locations of the 3He(7t~,r|)r transition

112


An experiment was performed us-ing the Crystal Box detector to studythe rare radiative pion decayjt —- evy. The distribution of energysharing between the three particlesin the decay yields information aboutthe ratio of axial-vector-to-vectorform factors that describe the struc-ture-dependent part of the piondecay amplitude. This information isimportant for nonperturbative quan-tum chromodynamics (QCD) calcu-lations of low-energy sum rules andfor providing important informationon the current quark masses. Twoprevious experiments obtainedsimilar results for the magnitude ofthe ratio but had conflicting resultsfor the sign.

The experiment used a beam of~ 105 7i+/s stopped in a thin target atthe center of the Crystal Box de-tector. The trigger required a coin-cidence between one charged andone neutral particle, each with aminimum energy of «15 MeV. The

effective branching ratio for n —* evyis ~ 10~B. We collected several hun-dred events covering a broad regionof the allowed phase space; the datashould easily resolve the ambiguityamong results of previous experi-ments.

The data analysis is proceeding.The absolute energy calibration ofeach of «400 crystals has been de-termined using the known energyspectrum from normal muon decay.The data tapes have been processedto select candidate events. The mostdifficult part of the analysis is theseparation of the signal from acciden-tal coincidences in the region of lowelectron energy and high photonenergy. Results are expected in a fewmonths.

EXPERIMENT 888— SMC

Study of the Decay n+ — e+v,r

Los Alamos, Stanford Univ., Univ. ofChicago, Temple Univ.

Spokesman: Aksel Hallin (Los Alamos)

Participants: ft D. Bolton.M. D. Cooper, J. S.Frank, A. L Hallin, P. Heusi, C. M. Hoffman,G. E. Hogan, F. G. Mariam, ft E. Mischke, LPiilonen, V. D. Sandberg, ft Werbeck, R. A.Williams, S. L Wilson, M. Ritter, D. Grosnick,S. C. Wright, V. L Highland, and J.McDonough

113

RESEARCH

Nuclear and Particle Phvsics


MEGA: Search for the Rare Decay

Argonne UCLA Uni\, oi Chicago. Univ01 Houston. Los Aiarnos Staniorcl•_'P,i\ , le . ' .dS A&M-- ,1 ' i u .•-•Mr. J\

Virginia Univ ol Wyoming, vale Univ

Spokesman: M. D. Cooper (Los Alamos)

Par'.icipants: K. F. Johnson, D. Barlow, B. M. K.Nefkens, C. Pillai, S. C. Wright, E. V.Hungerford. III. D. Kodayh, B. W. Mayes, II, LPinsky. J. F. Amann, R. D. Bolton, M. D.Cooper, W. Foreman, C. M. Hoffman, G. E.Hogan, T. Kozlowski, R. E. Mischke, D. E.Nagle, F. J. Naivar, M. A. Oothoudt. L E.Piilonen, R. D. Werbeck, E. B. Hughes, R. H.Burch, Jr., C. A. Gagliardi, R. E. Tribble,K. 0. H. Ziock, A. R. Kunselman, P. S. Cooper,R. Lauer, andJ. K. Markey

The search for processes thatviolate conservation of muon numbercontinues to be a subject of highinterest because these reactions mustoccur through processes outside theminimal Standard Model of weak in-teractions. In placing the observedfermions in the group representa-tions of the model, the assignmentsare repeated three times and theparticles are assigned to generationsor families in the order of their mass.However, the minimal StandardModel is aesthetically incomplete be-cause it contains many unknownparameters and the family replicationis not explained. The apparent needfor an extension to the StandardModel and the requirement thatmuonnumber nonconservation beoutside the model have driven ex-perimentalists to redouble their ef-forts to find such a process.Furthermore, its nondiscovery at in-creasingly better limits restricts thetypes of models that can be built.

The future of this field at LAMPF iscalled MEGA, an acronym standingfor Muon decays into an Electron anda GAmma ray, and is a search with abranching-ratio sensitivity of9 X l(T14. The MEGA collaboration,formed in the spring of 1985, sub-mitted the experiment proposal toLAMPF last summer. The experimentwas approved but awaits final DOEfunding approval, we hope by Febru-ary 1986. Meanwhile, substantial ac-

tivity has begun at most of the 10collaborating institutions. Ourreasons for beginning a new searchfor (i+ —* e+y follow.

1. The search addresses some ofthe most compelling physics issuesof the 1980s—that is, physics beyondthe Standard Model. Many of thepossible extensions of the StandardModel would make |i+ —• e+7 ob-servable. In many models the massscale probed would be well abovethe energies expected, even at theSuperconducting Super Collider(SSC).

2. MEGA will have a factor of500 improved sensitivity comparedwith that of the Crystal Box, which iscurrently the best detector for|i+ —• e+y. The factor of 500 improve-ment is the largest that can be madeon any of the reactions that have al-ready been studied at a significantlevel.

3. The |i+ —<• e+y is the easiest totackle at LAMPF. A \T beam of suffi-cient intensity to warrant undertak-ing the uT/4 —* e~A conversion ex-periment does not exist, and the costof a new beam line is prohibitive.Each of the muon branches has beenpushed to the limit of acceptablebackground, and the technical im-provements required fora three-par-ticle final-state decay are more com-plex at a low-duty-factor accelerator.

4. Substantial expertise alreadyexists at LAMPF from the uey/ andCrystal Box experiments for detect-ing this process.

114


5. The new technology used inthis experiment will raise the tech-nical expertise available at LAMPF.MEGA will

• be the first with a large cryogenicmagnet,

• demonstrate the ability to takedata in a very high intensity en-vironment,

• use a multicrate FASTBUS sys-tem, and

• use low-cost microcomputertechnology, both in data acquisi-tion and in replay, to achieve5 times the computing power ofthe Data Analysis Center.6. There is a window of time for

the next 5 years when LAMPF willhave the most intense beam for doinga high-sensitivity experiment.

In the design of the experimentseveral features are considered.

First, the sought-after process isidentified through the measurementof kinematical variables, that is, con-servation of the four-momentum. TheH+ —• e+y decay has the signature ofback-to-back electrons and photonsthat are in-time, each 52.8 MeV andfrom a common vertex.

To reach the very high sensitivity,the second requirement is a largenumber of useful muon decays,

o= - zRT

4TI

where Qo is the solid angle, e is thedetection efficiency, and RT'\s thestopping rate times the running time.

MEGA is designed for 50% accep-tance, high efficiency, and the high-est stopping rate consistent with detector performance. The detectoruses a low-energy stopped-muonbeam and a thin target to achieve itsrequired stopping density.

A third requirement is good reso-lution, which stresses technology inhigh-rate environments and which isneeded to suppress backgrounds ofeither allowed processes or acciden-tal coincidences. The experimentmust be background free so that sen-sitivity will improve inversely as therunning time, rather than inversely asthe square root of the running timewhen background is present. Thereare two sources of backgrounds:prompt-allowed processes and ran-dom coincidences. These back-grounds are suppressed with goodresolution.

Fourth, the data processing is asearch for a rare process in a verygreat number of decays. Hence, aclever trigger is designed to controldata-encoding and tape-writing rates,and sophisticated analysis is used toselect any possible candidates.

Finally, to understand the detectorresponse, the allowed process|i+ —• e+yvv is measured to prove thatthe instrument can observe what itshould.

115

RESEARCH


Electron Scintillator.Annular Arrays Electron MWPC

Target

InnerBremsstrahlung'Veto(IBV)

-Lead

-Magnet Wall

' Photon Converter,Scintillator, and Wire Chamber Layer

0.5 m —|

FIGURE 1 End view of the MEGA apparatus with an idealized \i+ —• e+y decayshown

The MEGA apparatus is shown inFigs. 1 and 2 and is designed to findthe decay u+ —• e+y in a background-free experiment if its branching ratiois greater than 1CT13. The apparatus iscontained in a large magnet that willbe obtained from SLAC; it has a fieldof 1.5 T, a clear bore of 1.85 m, and alength of 2.2 m. The central region ofthe magnet contains the target, whichis a thin planar ellipse canted at alarge angle relative to the beam. Thisorientation provides adequate stop-ping power in the beam direction tocontain the muons and presents aminimal thickness to the decayproducts. The expected stopping rateis3X 107 Hz (average).

The detector is divided into anelectron spectrometer and a series ofphoton pair-spectrometers. All thecharged particles arising from muondecay are confined to a maximumradius of 29 cm, leaving the photondetectors in a relatively quiet en-vironment. A low-rate photon arm isessential to the success of the experi-ment. The design philosophy of theelectron arm is to optimize the reso-lution of the electron detectorswithout producing photon backgrounds.

The electron arm consists of twoparts. The electrons from muondecay first pass through a multiwireproportional chamber (MWPC) withthree layers of sense wires at radii of6,11, and 14 cm. The chamber,

116


ElectronScmttllatO'AnnularArrays

Beam and

Direction

Lead • ^

Photon _Converter,Scintillator,and WireChamberLayer

\

'•*-'-•-•-"r»-"r'r"T"

CfSf\7

/YYwT' J ^ N y

"S- ^

• —--y ri M i n i ) i H H i

Electron/ MWPC

^ Target

Internal

strahlungVeto(IBV)

T0.5m

1Wall

FIGURE 2 A sectioned plan view of the MEGA apparatus with the same idealized(i+ —• e+y event shown that was displayed in Fig 1

which is built of the thinnest possiblematerials to minimize multiple scat-tering and positron annihilation inflight, also acts as a 180° spec-trometer to measure the helical pathsof the electrons in the uniform mag-netic field. The parallel componentsof the momenta are derived from themeasured coordinates of chamber in-tersections along the beam direction.These measurements are achievedwith spiral cathode strips. The wirespacing in the chamber is 1 mm, apitch that makes the chamber effi-cient at high rates. The chamber isgated with a short coincidence pulseto limit its sensitivity to the periods ofinterest.

The very high rate makes a seriouspattern-recognition problem. A typi-

cal event is illustrated in Fig. 3. Thekey to identifying candidate elec-trons is that in the end view theymake almost perfect circles. The sym-metry in a circle, plus redundancy inthe cathode strips, makes for a highlyefficient selection of candidates thatstill rejects useless events. Figure 4illustrates the expected resolutionsfrom the electron arm.

The second part of the electronspectrometer consists of banks ofscintillators arranged in a cylindricalgeometry about the beam near thepole faces. After at least one revolu-tion in the chamber, the electronsenter the scintillators, whichmeasure the time of the electron.

117


ISOElectron Energy Resolution

"10 -0.5 0 0.5 1.0

Energy (MeV)

Electron Angular Resolution80

SO

40

20

(b)

FWHM = 0.56(projected)

0 1 —-I 0 1 2 3

Angle (cleg)

FIGURE 4 The expected resolutionsIrom me MEGA electron arm in (a) energyand(b) angle The simulation includesresoiuhons ot the MVVPC and multiplescattering m the chambers and target

30 r

40 -i

0 -

1- 2 0 -

- 4 0

£Sdntillalor

Target

From* 4

-100 -BO -60 -40 "20 0 20 40 60 80 100Z(cm)

FIGURE 3 A typical event in the electron spectrometer

Electrons trapped in the field formore than eight loops are rejected bytheir relative time with respect to thephoton. Each bank is divided into100 elements to keep the individualcounter rates manageable. After pass-age through the scintillators, theelectrons are stopped in a 4-cm-thickannulus of lead.

The photon arm consists of con-centric pair-spectrometers of essendally identical construction. Ablowup of a section of one spec-trometer is shown in Fig. 5. Eachpair-spectrometer is made of leadconverters, MWPCs, drift chambers,

and scintillators. The converters aredivided into three sheets and are sep-arated by the MWPCs. Each sheet isthin enough to maintain good resolu-tion (1.2% at 50 MeV). The MWPCsdetermine in which sheet the inci-dent photon is converted, allowing acorrection for the mean energy lossin subsequent sheets to be made. Theelectron and positron from the con-version have most of their energymeasured by the drift chambers asthey move along helical paths whoseradii are proportional to theirperpendicular momenta. Theparallel components of momenta are

118

measured with spiral cathodes. Fi-nally, the particles recross the converters into a cylindrical hodoscopeof scintillators of 4 cm arc length.These scintillators, with photo-multiplier tubes at both ends,measure the time of the photon conversion. Contributions from energyloss straggling and chamber resolu-tion degrade the resolution to 2%.Bremsstrahlung produces a lowenergy tail for 50% of the spectrum.The expected response function ofthe pair-spectrometer is shown inFig. 6.

The most serious background forthe experiment is a 52.8-MeV electron from normal muon decay in acci-dental, back-to-back, and time coincidence with a 52.8-MeV photon. Themost copious source of 52.8-MeVphotons conies from internal brems-strahlung or radiative muon decay(|i+ —• e+yvv.) We intend to vetothese photons by detecting the nor-mally present low energy electronswith which the photons are as-sociated. These electrons are below2.5 MeV and follow the field lines tothe magnet pole faces. Relevant partsof the pole faces will be lined withscintillators set to veto on these elec-trons.

The very high in.;1 uaneous ratesrequire a sophisticated trigger. Theprimary trigger relies on the fact thatall electrons from muon decay arecontained in the central region of thedetector. If the trigger requires aphoton of at least 42 MeV, the num-ber of firings will be reduced by afactor of roughly 700 relative to themuon stopping rate.

RESEARCH


Typical Event in the Photon Arm

52.8-MeVy

X

0

X

o

X

X

o

~~ -

X

0

0 O*

_ X 2 - = ~

o o

X[ nrift

-Cathode Strips -

—Field Wires -

-Sense Wires

.„___ 3-MeVy

l5-k<T""~---

ConverterPlastic/Lead /MWPC

Sandwich

Chamber

.Field/

17-MeV e"

•O O

o o

DriftChamber

i-1 cm

H

FIGURE 5 A blown-up view ol one pair-spectrometer showing the multiple layers olconverters and the chambers and scintillators

Eve

ni

I00

50

-

—i-

-

°45

Reconstructed PhotonI ' I ' I

I.OMeV-

47 49 51Energy (MeV)

Energy

T:k T

—*T r—

/ \ "

53 55

FIGURE 6 The energy resolution expected Irom the pair-spectrometers

119


TABLE I Parameters ot | i + —• e+y Experiments

Properties MEGA \ieyl Crystal Box

Fractional electron energy resolutionFractional photon energy resolutionPhoton-electron timing (ns)Electron position resolution at the target (mm)Electron angular resolution, including target scattering (deg)Photon conversion point resolution (mm)Electron-photon angle (deg)Photon angle (deg)inethciency oi biemsstrahiung vetoFractional solid angle times detection efficiencyMuon-stoppmgra!e(s-' )Running time (s)Branching-ratio sensitivityNumber of background events with ±2o cuts

0 0050,020.52 00 630 6

100 20,1

3 X 107

1.2 X 107

8 X 10"M

0 4

0 090 0 82 03.01 3

763,8

0.0182X 106

1.1 X 10s

1.7X 10""'°- 1 0

0.080,081 12 01.3

258.0

0.50.2

5 X 105

2 X 106

4 X 1CT11

- 5 0

All resolutions are FWHM

On average, there will be 36 usbetween triggers, which is sufficienttime for modern electronics to en-code, compact, and read the data intomemories. A typical event will con-tain about 700 data words. The dead-time will be kept small by usingsubstantial parallel processing. At theend of a LAMPF macropulse, the datafrom the events will be read into oneof 32 microprocessors for furtherselection.

The additional criteria will requirethe electron energy to be 49 MeV, topass some restrictions on its relativetime to the photon, and to be within10° of back-to-back to the photon.The surviving events will be writtento tape at a rate of 11/s for furtheranalysis, which will use the completecalibrations and refined algorithms

to sharpen the detector responsefunctions, thus kinematically isolat-ing any u+ —* e+y events from allbackgrounds. The replay of the tapeswill be done with the data-acquisi-tion microprocessors.

The parameters of MEGA are sum-marized in Table I, where they arecompared with earlier experimentssince 1975. In almost every categoryMEGA makes significant improve-ments over the previous efforts. Theproduct of these improvements leadsto an experiment with an ultimatesensitivity that is 500 times greaterthan that expected in results from theCrystal Box.

To dramatize the sensitivity, Fig. 7displays the 90% confidence limitversus running time that can beachieved with MEGA. The currentlimit and the curve for the CrystalBox are also shown. In the back-ground-free region, the curves dropinversely as the running time, and in

120


the background-limited region theydrop inversely as the square root ofthe running time. The desirability ofa background-free experiment isclear.

The collaboration has estimatedthe cost of MEGA to be $2.9 million ifthe magnet is made available bySLAC. The Director of SLAC has justgiven his approval for the move. Ifthe funding is available to allow forrapid procuremeni, debugging of theexperiment can begin in the spring of1988. The collaboration:; veryenthusiastic about the experimentand is working hard to keep it onschedule.

MEGA is a world-class effort tosearch for muon-number non-conserving decays, and it comple-

ments experiments at SIN (muon-electron conversion1) and atBrookhaven (rare kaon decays3! tofind a violation of the StandardModel. We must explore all thepossible channels because theorygives very little guidance as to whichprocess will be easiest to observe.Unfortunately, there are so manypossible extensions to the StandardModel, each containing un-constrained parameters, that no de-finitive predictive power exists. Mostof the models introduce new parti-cles of large mass. Therefore, the newexperiments will continue to restrictthe model builders and give insighton what to expect at the new genera-tion of accelerators.

90% Confidence Limit*

•MEGA

10' 10*Live Time (s)

FIGURE 7. The branching-ratio sensitiv-ity as a function ol running time for MEGAand the Crystal Box

References

1. A. Badertscheret al., "Search forpT —* e Conversion," SIN letter of intentR-85-07.0, Villigen. Switzerland, 1985.

2. R. D. Cousins et al., "Study of Very Rare KL Decays," Brookhaven NationalLaboratory Alternating Gradient Synchrotron (AGS) Proposal 791,1984.

121


EXPERIMENT 914—SMCLAMPF

EXPERIMENT 791 — Beam B5Brookhaven

Study of Very Rare Kt Decays

L o s ~ > i a r ' X v ; ^ i r t n i o i f t 1 i r " ' i . I ' m . o i

Pennsylvania, UCLA. I einuie -JIV.College ot W'l.iam \Mar\

Spokesmen (J\MPF Exp. 797;: G. H. Sandersand W. W. Kinnison (Los Alamos)

Spokesman (Brookhaven Exp. 791): S. Wojcicki(Stanford Univ.)

As part of a major program of research in very rare KL decays, LAMPFExp. 91-i was proposed to measurethe analyzing power of a segmentedmuon polarimeter, a measurementessential to rhe design of the KL ex-periment and to the analysis of thesubsequent data.

The program of rare KL decay research is an approved experiment atthe Brookhaven National LaboratoryAlternating Gradient Synchrotron(AGS). Ina2500hexposuretoabeam of 1013 protons per pulse (witha 30 to 40% macroscopic duty factor)we will search for the decay KL —• uewith a branching-ratio sensitivity of~ 1 X 10~12, bettering existing limitsby many orders of magnitude. In ad-dition, the known decay KL -— u+u~will be simultaneously measured.This decay has a branching ratio of

Polarimeter.

Muon FilterLead Glass"

(Serenkov Counter!

:-ridiv;in9 Magnet

Dnt| ChamDers

n Counters

Target

9.1 X 10 9, and 27 events constitutethe world sample. The new experi-ment should collect ~ 10 000 ofthese events. We will search for thedecays KL —* ee and KL —- jt°e+t~ aswell.

The physics motivations for thesestudies address frontier particle-physics problems, and all are amongthe high-priority experiments thatwould be pursued a a LAMPF II fa-cility. The KL —<• \ieexperiment is asearch for nonconservation of nmonnumber, competitive with and com-plementary to the Crystal Box experi-ments and the MEGA (Muon decaysinto an Electron and a GAmma ray)project. The measurement of10 000 events for KL —- uu would farexceed the precision of previousstudies. However, the unique and ex-citing aspect of this new study wi 11 beour search for polarization of the n+

from the KL —» u.+u~ decay. The Stan-dard Model predicts no polarization,'<nid the present world sampleprovides no limit on the polarization.Therefore, observation of anynonzero polarization would signifythe presence of entirely new physics,beyond the Standard Model and mostlikely involving charge-parity (CP)violating mechanisms. This subjecthas been considered extensively bythe theoretical community, which in-cludes Peter Herczeg at Los Alamos.

The measurement of polarizationis the motivation for LAMPF Exp. 914.In the Brookhaven detector, Los Ala-mos will provide the largest detectorcomponent, a 300-ton, fully activemuon range finder/polarimeter. Fig-ure 1 shows the kaon-decay

FIGURE ' The rare kaon decay spectrometer

122

spectrometer, with the Los Alamospolarimeter at the downstream end.This module will measure the muonrange in real time, essential to theexperiment trigger. In addition,when fully instrumented it will locatethe stopping position of each muonand detect the time and direction ofcorresponding decay electrons. Theentire volume of the module will bein a vertical 60-G magnetic field. Themuon polarization will be unfoldedfrom the decay asymmetry observed.

To carry out the polarization meas-urement, the range finder/polarimeter must be con-structed of materials that induce noH+ depolarization at the stoppingpoint. For this reason, the 300 tons ofabsorber plates will be made of Carrara marble and the active trackingdetectors will be ~40 000 extrudedaluminum proportional tubes. Thiscombination is the lowest-cost sys-tem that meets the performance re-quirements, and these choices followthe developments in earlier experi-ments at CERN.

The polarization analyzing powerhas been carefully calculated usingMonte Carlo simulations. However,validation of these design calcula-tions requires empirical verification.In addition, the key parameter, theanalyzing power, must be measuredbecause many subtle, but significant,systematic effects cannot be reliablyincluded in any simulation. For thesereasons, LAMPF Exp. 914 wasproposed to determine the polariza-tion analyzing power, using theprecision control of \x+ polarizationavailable at the SMC.

RESEARCH


The prototype polarimeter moduleused is shown in Fig. 2. It was constructed jointly at the College of Wil-liam & Mary and LAMPF. It consists of256 channels of proportional tubesand provision for 3 absorber plates.The sensitive region of thepolarimeter is housed within aHelmholtz coil that provides the

TOP VIEWHELMHOLTZ COIL

POLARIZEDMUON BEAM

L

ABSORBER PLATE

~L

VIEW DOWNSTREAM

.VERTICAL TUBES/ ( 3 0 0 cm)

; risvt

HORIZONTAL TUBES(250 cm)

FIGURE 2. The test polarimeter used in LAMPF Exp 914

123

RESEARCH


necessary 60G muon precessionfield. The incoming muon beam ismeasured by upstream trigger scin-tillators, and tracks are defined bytwo sets of multiwire proportionalchambers. The polarimeter propor-tional-tube planes are read out into128-word-deep buffer memories,clocked at 10 MHz. The trigger issuch that for each stopped muon theentire history of the polarimetermodule is digitized for 6.4 \is beforeand 6.4 u.s following the muon stop.This provides a complete measure-ment of the niuon stops and decays.

The first of two data runs has beencarried out, using 133-MeV/cpolarized u.+at the SMC. By varyingthe source pion momentum in thecollection section of the SMC, thepolarization of the ji+ beam was ad-

justed between full forward and fullbackward polarization. A total of 106

stopped u.+ events was recorded, withdata taken under varying beam rates,absorber plate thicknesses, choicesof absorber material (6o6l aluminumand Carrara marble), and magnetic-field settings.

Figure 3 shows the observeddecay-electron counting rate in aselected proportional-tube region asa function of time after the muonstop. The data clearly show the n+

decay rate and the modulation result-ing from n+ polarization. The decayasymmetry from a preliminary fit tothese data is shown. The final analy-sis of all the data taken and the com-parison of the fit results with theMonte Carlo results will yield themeasurement of the analyzing powerunder the conditions studied. A sec-ond data run for Exp. 914 will berequested when the final detectorversion is constructed.

During 1986 a major part of theabsorber system and a significant partof the active detectors will be con-structed for use at Brookhaven inautumn 1986.

124

RESEARCH


FIGURE 3 Preliminary results from analysis of the test polarimeter data. The rawprecession spectrum is from chambers upstream and downstream of the muonstopping point. Marble absorbers (3.8 cm thick) were located in each gap. Fit resultsare shown below

103

E 1 4

o 1 2O

1 00 8

0 6

0 4

0 2

\

-

° 10

103

in

§2 4(

oO2.0

1 8

1 0\ c.

0 8

0 4

-

-

0 10

c^,

L ' 1 5

1 0

0.5

__

**

0 10

(a) Downstream plane hitsNBA

(0

<pX2

20 30 40 50 60Channel

= 927±15= 382± 5= 0,153±0,015= 0,517±0,008= 0,35 ±0.14= 33.5

(b) Upstream plane hits.NBA

0)

<P

x2

20 30 40 50 60

Channel

i

• J j l

1i i i i i

= 1288±23=1069± 8= 0.168±0.016= 0.499 ±0.008= 2.21 ±0.14= 77.3

(c) Subtracted results. The upper twocurves are subtracted, after remov-ing the flat backgrounds, and theplotted results are normalized to thesum of

A

B00

<P20 30 40 50 60 ^2

Channel

the two curves.= 0.154 ±0.012

= 1.2 ±0.008= 0.5077 ±0.0062= 3.798 ±0.108= 40.6

125



E2 and E4 Deformations in u*Th,I1I.ZM,US,UI,UI|J

Los Alamos, Princeton Univ , PurdueUniv . Oak Ridge

Spokesmen: E. B. Shera (Los Alamos) and J. D.Zumbro (Princeton Univ./Univ. ofPennsylvania)

Participants: C. E. Bemis. Jr., M. V. Hoehn, R. A.Naumann. W. Reuter, E. B. Shera, R. M.Steffen, V. Tanaka, andJ. D. Zumbro

Muonic x-ray spectra of 232Th,233,234,235,236,23BJJ a n c | 239,240,242 p

been studied over the past 3 years.*The primary purpose of the measure-ments was to make precise de-terminations of the nuclear electrichexadecapole moments in theseheavy nuclei. The quadrupole (El)moments, as revealed in this se-quence of experiments, show asmooth systematic increase with in-creasing atomic mass [Fig. 1 (a)]. Theelectric-quadrupole deformations in-ferred from the muonic hyperfinesplittings are in good agreement withresults2 obtained by other workersusing an independent experi-mental technique, Coulomb ex-citation. The agreement supports thevalidity of the interpretations of bothexperiments.

The precise new experimentalvalues for the hexadecapole (EA)moments of these nuclei are the mostsignificant results of our program[Fig. 1 (b)]. These values, 2 to 5 timesmore precise than the results fromCoulomb excitation, provide impor-tant new benchmarks-for Hartree-Fock and Strutinsky-type calculationsof the shapes of heavy nuclei. Theregular systematic trend of the EAdeformations in this region, like thatfor E2, is again evident. Note also thegenerally good agreement betweenthe present results and Coulomb ex-citation work by Bemis et al.2 (Theolder muonic-atom work of Closeet al.3 yielded much smaller EAvalues—the result, we believe, of animproper analysis formalism.)

Figure 2 shows sample muonic-Kx-ray spectra measured in our experi-ments. The complex hyperfine pat-tern and isotope shift is clearly evi-dent.

With the exception of 237Np, wehave studied all the actinide nucleithat are available in sufficient quan-tity (~ 10 g) for our experiments.

12

10

3

2

1

0

- 1

l I i l l I I i• Exp 754x Bemis el alo Close el al

• Exp 745

X Bemis el al (a.a)

O Close el al (|i~x rays)

. i

23G 235 240A

245 250

FIGURE 1.(a) The intrinsic quadrupole moment

(Oo) versus A. Values from thepresent experiment are comparedto results from other experimentsAlso shown is the value ol vanEnschutet al. (Refs. 4 and 5) for237Np and the values of Johnsonetal.(Ref. 6)for241243Ammeasured in Exp. 653.

(b) The intrinsic hexadecapole mo-ment (HQ) versus A. Values forisotopes ol the same element areconnected by dashed lines.

•Rslerence 1 gives the results lor232.234.235.238U T h e r e s u l t s ( o I 239,240,242pb

will be published in Physics Letters B)

126


Many of these nuclei are, of course,intensely radioactive and requirespecial techniques to obtain spectraof the quality shown in Fig. 2.

At the February 1985 meeting ofthe Program Advisory Committee(PAC), Exp. 745 requested time tomeasure "37Np. Almost simultane-ously the SIN data for "7Np were

presented.4 In Fig. 1 we show theintrinsic quadrupole moment of 237Npfrom the SIN work.5 Because the re-sult is quite different from the sys-tematic trend of the other isotopes inthis region, a verification of the SINresult clearly would be worthwhile.

500-

250-

0 -

500-

250-

0-

/"50-

% 500-

° 250-0-

250"

0-

750-

500-

250-

0 -

233U

234 y

2 3 5 u

Vi^-i

2 3 S U

^ ^ ^ ^

2 3 8 U

-A.- 1 1 „

I

i . LII

.- A i-i ' ' < r *

1.1 ii

K x rays

. .1 ,I I

i • i •

1 .• 1 i

' • 1 ' ' • 1 * ' ' • 1 *

AM 1

i

6000 6100 6200 6300 6400 6500 6600Energy (keV)

FIGURE 2 The 233.234.235.236.23Bu m u o n jC .K x rays and the computed (fitted) spectra.The latter is shown as a continuous line through the data points. The vertical linesbelow each spectrum indicate the computed (fitted) energies and relative intensities ofthe individual x-ray transitions. The excellent fit of the computed spectra to theexperimental data is Rvident; on the scale of these drawings the computed andexperimental spectra cannot be distinguished.

127


References

1. J. D. Zumbroet al., Physical Review Letters 53,1888 (1984).

2. C. E. Bemiset al., Physical Review C 8,1466 (1973).

3. D. A. Close, J. J. Malanlfy, andj. P. Davidson, Physical Review C17,1433(1978).

4. J. F.M.d'AchardvanEnschutet al., SIN Newsletter 11,44 Oanuary 1985).

5. J. F. M. d'Achard van Enschut et al., Helvetica PhysicaActa 58,925 (1985).

6. M. W.Johnson et al., Physics Letters 161B, 75 (1985).

128


Experiment 726, a search for the Cviolating decay of the neutral pioninto three gamma rays, completedtaking data at the end of August. Theexperiment used the Crystal Box asthe photon detector. The central driftchamber was replaced by a liquid-hydrogen target in which negativepions stopped and produced neutralpions by charge exchange. A suitabletune of the SMC for a negative-pionbeam had already been developed byus in preliminary studies and forExp. 888. A momentum of157 MeV/c was used, where wefound the beam to be approximately40% pions, 10% muons, and 50%electrons. The intensity was morethan adequate to deliver 80 kHz ofnegative pions. The only drawback ofthe channel was that control of themomentum bite was primitive. Rangestraggling and multiple scatteringlimited the fraction of pions stoppingin the 20-cm-long by 10-cm-diamliquid-hydrogen target to 50%. Froma study of the stopping distribution,we tentatively deduce a momentumwidth of about 6% FWHM.

Minimal changes to the elaborateCrystal Box electronics system wererequired to adapt it to the new trig-ger. The principal source of triggerswas expected to be the spreading ofone of the showers from a two-gamma decay of a pion to look like athree-gamma decay. Three differenthardware devices were included inthe trigger to insist on a minimumseparation between gammas and torequire a geometry consistent with athree-gamma decay. Another sourceof triggers was expected to be threegammas from multiple neutral pionproduction by two or more pions inthe same or adjacent LAMPF beambuckets. These were indeed copious,but were almost entirely eliminated


A Search for the C-NonlnvarlantDecay n1 - > 3y

Temple Univ., Los Alamos, Univ. olChicago

Spokesmen: Virgil Highland (Temple Univ.) andGary Hogan (Los Alamos)

129

RESEARCHNuclear and Particle Phvsics

TWO-GAMMA TIME DIFFERENCE

i n

LJ

1200

1000

800

600

400

200

0

i • i ' i i ^ i ' I • i i •

1.4 ns- i

- 5 - 4 - 3 - 2 - 1 0 1 2 3 4 5

TIME DIFFERENCE (ns)

FIGURE 1 Measured photon time dillerencetrom 7i°—•

. by a hardware rejection of high pu lseheight in the beam counters and asubsequent online rejection ofanomalous beam-counter pulseheights as measured by the CAMACanalog-to-digital converters (ADCs).

The experiment accumulated ap-proximately 3 million events on tape,and the analysis is under way, Theexperience accumulated from previ-ous Crystal Box experiments facili-tates the analysis considerably. A firstpass through the data has reducedthe data set by a factor of 10, based onloose time and energy criteria onthree adequately defined gammashower clusters. At the same time, asample of 3000 candidates for four-gamma decay was identified forfurther study. Time and energycalibration constants for all runs havebeen determined. The two-gammaevents have a time resolution of1.4 ns FWHM (see Fig. 1) and anenergy resolution of 10 MeV FWHMat 137 MeV.

The events remaining after the firstpass are completely dominated bythe spread of two-gamma showers tolook like three, as mentioned above.The geometry of the events clearlysuggests this to the eye, thekinematics supports the interpreta-tion, and a systematic time shift of thesplit-off gamma is observable. It isclear that considerable effort will beneeded to understand this phenome-non in detail as the data analysisproceeds.

130


Extensive discussions of these ex-periments have appeared in the pastseveral Progress Reports. The aim ofthese experiments is to search forseveral rare decay modes of the muonand to study these decay modesshould they be observed. The muon-number-nonconserving decaysu+ — e+e+e~, ]i+—- e+y, andH+ —>e+YY are being soughtwith a sensitivity to branching ratiosof about 4 X 10"" relative to ordinarymuon decay. The data also will beanalyzed to search for the decay\i+ —* e+yf, where / is the familon.

A schematic diagram of the CrystalBox is shown in Fig. 1. The detectorconsists of a modular array of396 Nal(Tl) crystals that surround anarray of plastic scintillation countersand a high-resolution., narrow-stereo-angle drift chamber. Approximately5 X 105 u.+/s (average) are stopped ina thin polystyrene target located inthe center of the detector. Electronand positron trajectories aremeasured in the drift chamber andtheir arrival times are measured inthe plastic scintillation counters. Theenergies of electrons, positrons, andphotons are measured in the Nal(Tl).The energy is determined from thelocal high-pulse-height crystal andits surrounding 24 neighboringcrystals. The photon-conversionpoints are also determined in theNal(Tl). Photons do not register ineither the drift chamber or the plasticscintillation counters.

In the search for all three decaymodes, data were acquired simulta-neously during summer 1984. Thepast year has been spent calibratingthe detector and analyzing the data.The major source of backgrounds isthe random coincidence of e+'s andY's from the uncorrelated decays ofseveral muons. This background iseliminated by requiring that the de-tected particles be in time coin-cidence and that they satisfy conser-vation of energy and momentum. Forthe |i+ —- e+e+e~ mode there is theadditional constraint that the threetracks must emerge from a commonvertex. To reject the backgrounds toan adequate level, excellent resolu-tions in timing, energy, and positionare required.

The primary calibration of theNal(Tl) is accomplished by remov-ing the drift chamber, inserting asmall liquid-hydrogen target in thecenter of the apparatus, and retuningthe beam to stop 7t~'s in the hydro-gen. Calibration photons areproduced in the reactions iCp —- n°nno _ yy (55 M e V < Ey < 83 MeV),and iCp —• ny (E^ = 129 MeV) .Fig-ure 2 shows the total energy for thetwo photons from 7t° decay aftercalibration. The energy resolution isAE/E=7.2%.

EXPERIMENTS400/445— SMC

Crystal BOM Experiments

Los Alamos, Stanford Univ., Univ. ofChicago, Temple Univ.

Spokesman: C. M. Hoffman (Los Alamos)

^ Drift^ Chamber

Stoppinglet

Nal(TI)Crystals

Hodoscope'Counters

0 20 40cm

FIGURE 1 Schematic diagram of theCrystal Box detector

131

RESEflRCHNuclear and Particle Physics

3500

3000

^ 2300

£ 2000

5 1500

1000

300

Total Datacted Energy for ir—)

P,. «28.l MeV/c

no 130 isoEnergy (MeV)

FIGURE 2 The sum ol the photonenergies liom the reaction

K~p —» rut0

(at rest) as measured with the Nal(TI)

Once the crystals are calibratedwith the pion data, we must trackdrifts in the gain of each crystal (andits associated electronics) over thecourse of the data taking. The gain ofeach crystal relative to the average forthe entire array is tracked with axenon flash tube that is connected toeach crystal with fiber optics cables.Flasher runs were taken every 2 h.Although the flasher system is quiteuseful in tracking gain shifts andmalfunctions in individual channels,it is not stable enough to determinethe absolute gain shift of the entirecrystal array. For this purpose theNal(Tl) spectrum for positrons ineach quadrant, accumulated for eachdata run (every 2 h), is used. Thestability of the sodium iodide gains ischecked with daily calibration runstriggered by single positrons. The re-sulting Michel spectrum is then fittedwith the expected shape from theMonte Carlo program, as shown inFig. 3. Analysis of this procedure in-dicates that the gain of.the crystalarray in each run is constant to within0.5% and that the overall gain is cor-rect to better than 0.25%.

The energy deposited in eachNal(Tl) crystal is measured by inte-grating for 200 ns the pulse from aphotomultiplier coupled to thecrystal. It is necessary to eliminatepileup, which is energy present during the integration gate from addi-tional early or late pulses. This wasaccomplished with a second systemthat integrated the pulse over a 50ns

gate that included the leading edgeof the pulse. If a crystal has no pileup,the ratio of these two integrations is aconstant that reflects the pulse shape:

Detected Michel Positron Spectrum

250

25 45 SS

Energy (MeV)

FIGURE 3 The measured energyspectrum for ordinary muon decay

piledup crystals have ratios eitherlarger or smaller than this constant,depending on whether the pileuppulse occurs before or after theprompt pulse. If any crystal in aclump of 25 crystals has more than2.5 MeV and pileup, the clump is dis-carded. Any piledup crystal with lessthan 2.5 MeV is removed from theclump but the clump is retained. Ap-proximately one-third of the data wastaken without the pileup rejectorworking. For these data, themeasured pileup spectrum is addedto the Monte Carlo. For the data takenwith the pileup rejector, no residualpileup can be detected, as evidencedby the complete agreement of datataken with instantaneous muon-stop-ping rates differing by a factor of 2.

The analysis of the u —• ey data isnearly complete. The trigger con-dition for these data required apositron quadrant [a scintillator firing

132


plus =35 MeVintheNaI(Tl)]incoincidence with an opposite photonquadrant [ = 35 MeVin theNal(Tl)with no scintillator firing). Approx-imately 10% of the data were takenwith higher energy thresholds. Theresulting events can come from(i —» ey, inner bremsstrahlung{\X —* eyvv, a process that conservesmuon number), and random e+ ycoincidences. There were about 107

triggers. To determine the number ofeach kind of event, a maximum likelihood analysis was performed on the24 850 events, satisfying

i f , - / , | < -2.0 ns ,

£, > 4(1.0 MeV ,

Ee > 44.0 MeV ,

and

> 160° .

The likelihood function is defined as

£(Ct,p) = AT1 n [«/>(*) +

4- ( . V - a -

where a, (3, and (N— a— p) are thenumber of u —• ey, inner bremsstrah-lung, and random coincident events,respectively, and P, Q, and R are theprobability density distributions forthese kinds of events as a function ofthe variables Ee, £,, G^.and te— ty. Inthe maximum-likelihood method,the maximum of the likelihood func

tion in a,p space is found. Figure 4shows the likelihood function and itsprojections on the a and p axes. Theobserved number of inner brems-strahlung events (3475 ± 75) agreeswith the expected number within er-rors. The likelihood function peaks ata = 0, with a 90% confidence levelupper limit of a < 11; this cor-responds to a branching ratio of ap-proximately 5 X 10~u. The final re-sult awaits a full analysis of the detection efficiency and the number ofmuon decays observed.

Preliminary results for u —» eeeand u — eyy were presented in lastyear's Progress Report. The full analy-sis of these data will be completed inearly 1986. An additional preliminaryresult was presented at the Washington American Physical Society meet-ing in April 1985 for the decayP~* ey/where/is a familon, a mass-less scalar boson associated withfamily symmetry (this work was donewithT. Goldman of Group T-5). Thepreliminary result was

T(u — eyf)— <1.2X10~8(90%C.L.) ,evv)

corresponding to a lower limit on thescale of family symmetry breaking of9 X 108 GeV. The final result shouldbe roughly an order of magnitudemore sensitive to the symmetry-breaking scale.

- T T T T T M 'o \\\\}mrr--~'\o VrrnH n

FIGURE 4 The normalized likelihoodfunction plotted as a function of Ihe num-ber of muon inner bremsstrahlung eventsand the number of j i + —» e+y events Theprojected distribution on the /V^ like-lihood plane is also shown

133

RESEARCH


ATOMIC AND MOLECULAR PHYSICS

Theory of Muon-Catalyzed Fusionjames S Cohen and M Leon (Los

The remarkable ability of a singlenegative muon to catalyze many dtfusions is now firmly established, andsystematic research is under way todisentangle the intricacies of thecatalysis cycle.1"1 An essential contributor to the rapidity of the cycle isthe resonant molecular formationmechanism, in which the colliding/|i + d form the loosely bound./= 1,c = l dt\y mesomolecular ion, withthe energy released going into thevibration and rotation of the resultingcompound molecule |[(rf/(i.)rf2e]*,etc.}. The kinetic energies (andtherefore the target temperatures forthermalized fp. atoms for which thecollisions are resonant) are readilydetermined once the dt\a bindingenergy, the hyperfine splittings, andthe compound molecule "rovibra-tional" energies are known.

Recently, Breunlich et al.2 re-ported a catalysis experiment at SINusing a low-density (1% LH2) DTtarget (with tritium fracrionC, = 0.88) in which a rapidly decay-ing transient was seen in the appear-ance of the 14-MeV neutrons from dtfusion. In analogy with earlier ex-perimental results on dd\\. fusion,1'they interpret this transient in termsof a triplet-quenching hypothesis2 inwhich (i) the thermalization lime ofthe t\i atoms is neglected, (ii) themolecular-formation rate for triplett\i is very large ( ~ 109 s~l) for a ratherlow temperature (30 to 300 K), and(iii) the quenching rate for the trip-let t\i depends strongly on temperature.

However, in regard to (i), by usingthe cross sections calculated byMelezhik et al.6 for the scattering of1-eV ground-state t\i atoms from dand t, one finds for C, = 0.88 anelastic-scattering rate of only~2 X 109 cp s~\ where (pis the den-sity in units of LH2 density(4.25 X 10" atoms cm"3), so that thethermalization time is clearly notnegligible for (p = 1%.

An objection to (ii) comes fromconsidering the energy balance: If weignore the rotational contributions,the resonance energy for triplet t\icollisions with D2 is about 219 meV;for DT, 107 meV. Henre neitherchannel can contribute for a /u. atomthermalized at 30 K. One need nothave confidence in the theory of res-onant molecular formation78 tosubscribe to this conclusion, becauseit follows directly from the energy-balance equation [see Eq. (7) below].

An objection to (iii) is that solarge a temperature dependence isnot expected for the triplet-quenching rate, the process beingdominated by triton exchange'['H(TT) + ' U ) - ' H ( 1 P + tc\)}.Breunlich et al.2 point out this dis-agreement, but an even more seriousdiscrepancy is suggested by data re-ported earlier for 10% tritium,10

which has the transient falling offmuch more rapidly. The triplet-quenching model then implies thatthe quenching cross section isgreater for t\i. + d collisions than fort\x + t collisions, a situation thatclearly contradicts the well-foundedidea that / exchange dominates thet\i — /quenching.

For these reasons, therefore, wecannot accept the triplet-quenching

134

RESEARCHAtomic and Molecular Physics

hypothesis. (Breunlich et al.2 in-cluded the caveat that different theoretical explanations of their datashould be considered, too.)

Instead, we believe that the tran-sient in the neutron appearance ob-served by Breunlich et al.2 is due to anew phenomenon with significantimplications: epithermal molecularformation* Specifically, we proposethat the observed time dependenceactually represent the population oftn atoms passing through the energyregion of rapid (resonant)mesomolecular formation duringthermalization. Several elementscontribute to the argument:

1. the population of energetic(~ 1-eV) ground state tu atomsgrows as the target density <p isreduced;

2. thermalization slows as thetritium fraction or the targettemperature is increased;

3. the molecular-formation ratesfall rapidly as the effective tem-perature of the t\x. kinetic-energy distribution falls below~ 103 K; and, furthermore,

4. the dipole formation mecha-nism, in which the tfx + d sys-tem makes a dipole transition to

the looselybound/= 1, r= 1dt\i state, is actually less impor-tant than direct formation, inwhich .'n and d approach in arelative p wave and form thebound state with no dipole tran-sition involved.

We now deal with these four pointsin detail.

1. The influence of the targetdensity on the population ofenergetic t|i atoms comes from therole that radiation plays in /|i deex-citation. The relevant rates for n = 4and 3 are shown in Table I. (Starkmixing is strong enough for (p > 1%that we do not have to consider thedifferent 9. levels separately.12)Ponomarev1 has pointed out the im-portance of elastic scattering of excited /|J. atoms to the thermalizationprocess. Adopting the a]i.+ d excited-state elastic-scattering ratesA.,,(«) ofMenshikovandPonomarev13 for ty +t (for 1-eVkinetic energy) gives the products ofrate times lifetime Xetx shown inTable I. Because about half thekinetic energy is lost at each col-lision, a rough measure of the surviv-ing fraction of kinetic energy is given

The Dossibilitv o! epitheirnal molerular lormalionhas beerwais^L) be'Q'B especially Dv .I RalelsKiRei I 1

Thus we see from Table I that thefractional energy surviving the n = 3

TABLE I Dee<C'tation and Elastic Scattering Rates for Excited t\i Atoms a

n= 4 n = 3

A.e8T

' 00 1001

q

00

aExternal Auger (A.e

5

9510

0 060 060 06

1 91 81.1

1 20 120 0 1

000

191919

1 and radiative (A..J deexcitation rates and the product \efi lor excited l]i atomsand A.ej are taken IromMenshikov and Ponomarev. Rel 13. X8j is Irom their d(i- drates Units are 10

6.30.

71

5

The Xe

135

RESEARCH


state increases drastically as (p is de-creased. Although the kinetic energyupon arrival at n = 3 is not knownwith any degree of confidence, it haslong been thought12 to be ~ 1 eV (theexact value is not critical to our argu-ments as long as it is » kT). lrordefiniteness we assume that thepopulation of epithermal ground-state /|i atoms is Maxwell-distributed,with an average energy of 1 eV.

2. Elastic scattering of (ground-state) t\x atoms by rfand / has beencalculated by Melezhik et al.6 A strik-ing result is that the cross section forscattering from / is an order of magni-tude smaller than that from cl. Thisimplies much faster thermalizationfor lower tritium fraction and thus,according to the epithermalhypothesis, a much faster decay ofthe transient, as observed byBreunlich et al.10 Furthermore,thermalization through the region of~ 103 K clearly must take longer asthe target temperature is increased,explaining the temperature de-pendence of the transients.210

The time evolution of the non-equilibrium t\i energy-distributionfunction/(£,/) is determined (forarbitrary target temperature and com-position) by a Monte Carlo Simulation of the time-dependentBoltzmann equation.H W? use thecross sections of Ref. 6 and some less-accurate values for fu. + /scatteringabove the 0.24-eV inelasticthreshold15 (adjusting the latter to beconsistent with the former). As anapproximation we separate the calcu-lation of the slowing from that of

molecular formation and ignore theeffect of molecular formation onf(E,t), Time t= 0 corresponds to thearrival of the t\x atom at its Is groundstate. According to the calculations ofMarkushin,16 the cascade from a free\JT with 2-keV kinetic energy to the Isstate takes only ~0.1 nsfor(p=l%.Thus the unexplained rise seen inthe SIN experiment,2 which takes~50 ns, is presumably because the/ = 0, t\i kinetic-energy distributionis significantly above the energy atwhich the (epithermal) molecular-formation rate is maximum. Hencethe low-density muon-catalyzed dtfusion experiments present an op-portunity to gain unprecedentedknowledge of the t\i cascade.

3. The dipole molecular-forma-tion rates are calculated followingVinitskyet al.7and Leon,8 but includethe electron-shielding correctionpointed out by Cohen and Martin.17

As long as the resonances involved(for a given vibrational excitation)are not close to threshold, we can,rather than include the many dif-ferent individual resonances, sum toa good approximation over all thefinal molecular rotational states, ig-noring the rotational energy dif-ferences. Then, instead of the manypartial-wave terms of Ref. 8, the sumrule gives

Kf J

/ •

'O(P) J 'V(P)

X \dp'yo(p')yv(p')#(p')jQ

(1)


where the yt are the vibrational wavefunctions, j0 is the zero-orderspherical Bessel function, k2 is thetn + D2 (DT) relative momentum,TI= 1/2(3/5) for D2(DT) collisions,and <?(p) is the electric field from thespectator nucleus plus electrons.17

For D2 collisions we include con-tributions from v = 2 through 5; forDT, v = 3 through 6. We use the sumrule for all but the lowest v value.The results for singlet t\x atoms areshown in Fig. 1. In general, v = 3gives the dominant contribution, butfor D2 collisions at low temperaturethe v = 2 contribution is largest. Theweighted sum of these contributionsappropriate to C, = 0.88 does indeedfall for temperature <103 K.

The temperature in Fig. 1 is notthat of the target, but rather itcharacterizes the kinetic-energy dis-tribution in the f|i + D2 (or DT) cm.system. As one can readily show,when the projectile (t\i) Maxwelldistribution (with temperature Ta) iscombined with the target-molecule(D2 or DT) Maxwell distribution(Tb), the result in the cm. system isalso a Maxwell distribution, with tem-perature Tcm=(maTb+ mbTtt)/{ma +mb), where ma is the projectile massand mb is >he target mass.

4. The direct molecular-forma-tion process has not previously beenconsidered. We approximate it bymaking use of some results ofMelezhiket a I.6 and by assuming thatthe p-wave t\i + <tf elastic scattering isdominated by t h e / = 1, v= 1 state

with binding energy1 eb — 0.64 eV. Inthe present formulation we need todeal with collisions of t\x, both with adeuteron and with the D2 (or DT)molecule. We follow the conventionof using M,, &,, and Ex for the reducedmass, relative wave number, andcm.-system collision energy, respec-tively, for the former, and A/2, k2, andE2 for the latter. We write the p-waveelastic-scattering cross section as

1271a* = —

k\

(2)

with the elastic width Tet(kx) (inelectron volts) being given by

r\,,(/fe,) = a^k\ + a2k\

= 0.65 E\n + 0.049 £, (3)

(Ex is also expressed in electronvolts). The a5k\ term is due to thebound state at —6;,, and «3 is chosento fit the calculated values ofMelezhiket al.6The a2k\ term comesfrom the known long-range polariza-tion potential.18 Equations (2)and(3) describe the results of Ref. 6 ex-tremely well.

FIGURE 1. Epithermal molecular-lormationrates as functions ol cm. temperature. Theupper curves are the direct process; the lower,the dipole (times 10) for D2 (broken curves)and DT (solid curves) collisions (normalized toC d=<p=1)

137


We make the jump from elastict\x + dscattering to resonantmesomolecular formation in t\\. + D2

(or DT) collisions using the impulseapproximation. This method haspreviously been applied to rovibra-tional excitation in collisions ofatoms with diatomic molecules,19 aprocess that is closely related todirect mesomolecular formation. Thebasic assumption is appropriate fort\i. + D2 collisions, even at relativelylow energy, because the small neu-tral f u atom interacts significantlywith a deuteron only at distances thatare small when compared with typi-cal internuclear distances of D2. Inthe impulse approximation (with ap-proximate treatment of the internaltarget momentum, as shown below),the molecular-formation cross sec-tion can be written as the product

(4)

In this expression, (v,A^;0,Ar,)s<v,^|exp(/Ti^-p)|O,A:;>is the molecular hound-state formfactor. We define the quantity ap tobe the result of taking the p-waveamplitude off the energy shell; as themolecular binding is turned off,

In approximating dp in Eq. (4), weare guided by the fact that the scatter-ing is strongly dominated by thebound state. Expressing the energydenominator in Eq. (2) in terms of E2

to describe the molecular collision,we write the final result

(5)

X

In this expression,

re!(fei) is the "entrance width," Ydeex

is the deexcitation rate for allprocesses (from the compound-molecule state formed in the col-lision to states with too little energyfor the system to "back decay"20), andr,0, is the total width of the com-pound-molecule state. Presumably,Tdeex is dominated by Auger deexcita-tion,21 but collisional deexcitationmay contribute at large <p.

We take the internal target motioninto account in an approximate wayby averaging over the deuteronmomentum in the initial molecularstate; this gives the relation between£, and E2,

£ .= -M,-M2

M, ( \ \•Tl - I - F' + F' I

md \ 2 7

(6)

138

RESEARCH


where md is the deuteron mass and

Hi.)

is the initial rovibrational kineticenergy. The resonance energy Em isgiven by the energy balance equa-tion.

£ „ = E{- If,',- f E K< AE,y i

(7)

Here, E[ (E{) and E'K. (E{f) are theinitial (final) vibrational and rota-tional energies and Ae^ gives thedifference in hyperfine energies inthe t\L and dt\i. states.

Because we expect that Tdeex = F,o,and that r,o, <i E,, the integral overenergy.

ciE2/(E2lt)G%ec,(E2) , (8)

becomes a sum over resonances andthe dependence on r,ol disappears.Furthermore, we can with sufficientaccuracy use the sum rule result[analogous to Eq. (1) but with theelectric-field $(p) factors missing]for all but the lowest vibrational contribution to the direct process. Thesame v values are included as for thedipole mechanism; the dominantcontribution is from v = 3. Consider-ations of the initial D2 rotationalstates are also the same as for thedipole mechanism."

The resultant direct contributionsto the singlet D2 and DT molecular-formation rates as functions of 7"c m

are shown in Fig. 1. The direct process is more than 20 times strongerthan that for the dipole, and theweighted sum falls for 7"cm < 103 K.(The triplet rates are similar to thesinglet ones, allowing us to avoidexplicit treatment of triplet contribu-tions and quenching.)

With the above four elements inhand, we combine the energydis-tribution function/(£2,f) with thetotal molecular-formation cross sec-tion amf(E2) to give the time-depen-dent molecular-formation rateXdlll(t), shown in Fig. 2, for targettemperatures 30 and 300 K andC, = 0.88. As expected, more-rapid t\ienergy loss for the 30 K target resultsin faster decay of the transient, inagreement with the SIN experiment.2

Furthermore, the time scale of boththe rise and decay of the molecular-formation rate is in good agreementwith the experiment. The magnitudeof the peak in Kdlv,(t) also agreesfairly well with the values(8-9) X 108 s~\ quoted by Breunlichet al.2 (which they call triplet).

In addition, on the basis of thepresent epithermal molecular-forma-tion hypothesis, we predict that theamplitude of the transient signal willdecrease as the target density is in-creased (see Table I). The triplet-quenching hypothesis implies nosuch dependence.

FIGURE 2 Tirr,e dependence oi the molecu-lar-!ormation rate for Q = 0 88 and <p — 1 ?(Xdtfl normalized to Cd = (p = 1, muon decayts not included)

139


In conclusion;1. The triplet-quenching

hypothesis is probably not aviable explanation of the SINexperimental results.

2. The epithermal molecular-formation hypothesis appears tobe in good agreement with ex-periment and with theoreticalexpectations.

3. Observation of the density de-pendence of the amplitude ofthe transient in neutron produc-

tion would provide additionalevidence for choosing betweenthe two hypotheses.*Direct mesomolecular forma-tion is more important than thedipole mechanism.The detailed time dependenceof the transient offers usvaluable and hitherto un-available information on the tpcascade and collisionprocesses.

•Evidence lor such density dependence has beenseen in the LAMPF dt catalysis data (inlormation isfrom A M Anderson, Jackson, Wyoming. 1985)

References

1. L. I. Ponomarev, AtomkernenergieKerntechnik 4$, 175 (1983).

2. W. H. Breunlichet al., Physical Review Letters 53,1137 (1984).

3. S. E.Jones et al., Physical Review Letters 51,1757 (1983); S. E.Jones,"Some Surprises in Muon-Catalyzed Fusion," Atomic Physics IX, R. S. VanDyck, Jr., and E. N. Fortson, Eds. (World Scientific Co., Seattle, Washing-ton, 1985), p. 99; and "Progress at LAMPF," Los Alamos National Labora-tory report LA-10429-PR (April 1984), p. 89.

4. V. M. Bystritskyet al., Zhiirnal Eksperimental'noi i Teoreticheskoi Fiziki80,1700 (1981) [SovietPhysics-JETP 55,871 (1981)].

5. P. Kammel et al., Physical Review A 28, 2611 (1983).

6. V. S. Melezhik, L. I. Ponomarev, and M. P. Faifman, Zhurnal Eksperimen-tal 'not i Teoreticheskoi Fiziki 85,434 (1983) [Soviet Physics-JETP 58, 254(1983)].

7. S.I. Vinitsky et al., Zhurnal Eksperimental 'not i Teoreticheskoi Fiziki 74,849 (1978) [SovietPhysics-JETP47,444 (1978)].

8. M. Leon, Physical Review Letters 52,605 and 1655 (1984).

9. A. V. Matveenko and L. I. Ponomarev, Zhurnal Eksperimental 'noi iTeoreticheskoi Fiziki 59,1593 (1970) [Soviet Physics-JETP 32; 871(1971)].

140


10. W. H. Breunlich et al., "New Experimental Results on Muon CatalyzedFusion in Low Density Deuterium-Tritium Gas," Fundamental Interac-tions in Low-Energy Systems, P. Dalpiaz, G. Fiorentini.andG.Torelli,Eds. (Plenum Press, New York, 1985), pp. 449-457.

11. J. Rafelski, Exotic Atoms '79, K. Crowe et al., Eds. (Plenum Press, NewYork, 1980), p. 203.

12. M. Leon and H. A. Bethe, Physical Review 127,636 (1962); and M. Leon,Physics L etters 35B, 413 (1971).

13. L. I. MenshikovandL. I. Ponomarev, USSR preprints IAE-4006/12 andIAE 4041/12.

14. K. Koura Journal ofChemical Physics 65,3883 (1976).

15. A. V. Matveenkoand L. I. Ponomarev, Zhiirnal Eksperimental 'noi iTeoreticheskoi Fiziki 58,1640 (1970) [Soviet Physics-JETP 31,880(1970)]; and A. V. Matveenko et al., ZhurnalEksperimental'noi iTeoreticheskoi Fiziki 68,437 (1975) [ Soviet Physics-JETP 41, 212(1975)].

16. V. E. Markushin, Zhurnal Eksperimental 'noi i Teoreticheskoi Fiziki 80,35 (1981) [Soviet Physics-JETP 55,16 (1981)].

17. J.S. Cohen and R. L.Martin, Physical Review Letters 53,738 (1984).

18. T. F. O'Malley, L. Spruch, and L. Rosenberg, Journal of MathematicalPhysics 2,491 (1961).

19. A. Bogan, Physical Review A 9,1230 (1974).

20. A. M. Lane, Physics Letters 98A, 337 (1983).

21. L.N. Bogdanovaet al., Zhurnal Eksperimental'noi i Teoreticheskoi Fiziki83,1615 (1982) [SovietPhysics-JETP56,931 (1982)].

22. M. Leon andj. S. Cohen, Physical Review A 31, 2680 (1985).

141


EXPERIMENT 727and SMC

Biomed

Measurement of the Efficiency ofto son Catalysis In Deuterlum-Triiium Mixtures at High Densities

Br.gham Young Ur,v , Idaho Mational

Enqme^rmq I abOMitorv Los Alamos

Spokesman: S. E. Jones (Brigham Young Univ.)

Participants: A. N. Anderson, J. N. Bradbury, A. J.Caffrey, J. S. Cohen, P. A. M. Gram, M. Leon,H. ft Maltrud, M. A. Paciotti, C. D. Van Siclen,and K.D. Watts

Fusion

FIGURE I The mam c/f/i-catalvsis cycle

Other channels (not shown) are dis-

cussed m the text

The study of muon catalysis of dtfusion (see Fig. 1) has now entered aperiod of rapid development,13 just afew years after the experimental con-firmation by Bystritsky et al.* that dt\xmolecular formation is indeed fast onthe scale of the muon lifetime(2.2 us). In the 1983 and 1984 LAMPFProgress Reports und in Refs. 1 and 2,we reported the first measurementsof some of the basic parameters ofthis fascinating process. In particular,the sticking probability to, wasmeasured and the dt\i formationrates Xdv-d and A.dm_, for collisions oft\x atoms with D2 and DT moleculeswere determined as functions oftarget temperature T. Targets ofwidely varying tritium fraction C,(but only two values of density (p)were used, where (p = 0.45 and 0.60(relative to liquid-hydrogen density,4.25 X 1022 atoms/cm3). We have nowmade measurements over a muchlarger range of q> and have conse-quently discovered some new andunexpected phenomena: both cos andXdtp-d vary strongly with density (p.These observations indicate clearlythat in spite of extensive theoreticalefforts5 our understanding of muon-catalyzed dt fusion is still in-complete.

The experiment was performed us-ing the methods described in theearlier reports.1'2 In Fig. 2 we showthe cp dependence of the normalizedmuon-cycling rate Xc = A.°te/q> (whereA.°ta is the observed cycling rate) for a

variety of temperatures and tritiumfractions. It is conventional to nor-malize to liquid-hydrogen densitybecause of the expectation that allrelevant rates scale linearly with den-sity. The cycling time (= 1 A f s ) isdominated by the time the negativemuon spends in the Juatom groundstate waiting to transfer to a triton(rate<pA.d,C,), and that spent in the t\iground state waiting for molecularformation to occur (rate <pkd¥Cd,where Cd is the deuterium fraction).Thus we write*

JLK

(1)

The product quCd is the probabilitythat the muon will reach the d\iground state; qu will deviate fromunity, both because of muon transferto /from excited states of d[i (Ref. 6)and because the initial atomic-cap-ture ratio might differ somewhat fromthe ratio Cd/C,.

At the time of the present experi-ment the only predicted source of(p dependence was the factor qu.However, Fig. 2 shows clearly that,contrary to expectation, the(p dependence is least at small C,,where the first term of Eq. ( l ) i sdominant, and is most when strikingat large C,, where the second termdominates. Hence we are forced toconclude that the normalized molec-ular-formation rate X.dm increaseswith (p. Thus dt\i formation, whichoccurs via the resonancemechanism,710 is probably n^t apurely two-body collision process aspreviously assumed.

•Here all f/i atoms are Irsaled alike and hyperlmequenching ellecls are ignored

142

BESEABCH


Separating the contributions of thetwo terms in E (1) is complicatedby the possibiluy that qu may dependon both C, and <p and require furtherassumptions. Our procedure is firstto estimate Xdni from the high-C, dataand Xdt/qu from the low- C, data, andthen to use these values as the starting point for a global fit.* We assume that Xd, depends only on Tandthat all residual dependence ofXd,/qis on (p and C, is due to c/u. Incontrast to recent calculations ofMenshikov and Ponomarev6 (MP),who predict values t/"p that fallprecipitously with increasing C, and<p, our results suggest a relativelyweak dependence on C, and negligible dependence on (p. For example,for T, = 0.5 and T= 300 K, we obtainXdl/qls = (4^6 ± 93) X 106 s~' at(p = 0.12 and Xdl/qu = (457 ± 58) X106 s"1 at cp = 0.72, whereas MPpredict an increase by over a factor of2 (<T£P decreasing from 0.195 to0.085). Similarly, for C, = 0.04,T = 300, K, and (p = 0.72, we obtainXdt/qu = (328 ± 25) X 106 s~\ This isonly a factor of ~ 1.5 less than that atthe higher C, = 0.5, compared withthe predicted decrease by a factor of~-7 (<7*y = 0.62 for C, =0.04).**

On the other hand, our results forqu are consistent with recent ex-perimental findings12 for n~ capturein mixtures of hydrogen and deute-rium at (p < 0.11. Extrapolating fromthose results, which show no densitydependence, we infer that qu = [1 —( 1 - 7 , )Cx\{y2)

lc*,withy, = 0.81 ±

0.01,Y2 = 0.83±0.01,andx= tf forachemically equilibrated mix ofH2 /HD/D 2 . Then, using the samefunctional form to analyze our data,we find (now with .v= t) thaty, = y2

= 0.75 ± 0.20 and that A,,,, =* [1 +(6±1)X1O-4 T]t2?,U±40)X106 s"1 for the temperature rangefrom 20 to 500 K. This value of Xdl

agrees with the low<p, low C, experiment of Bystritsky et al.1* The temperature dependence is not quite asstrong as that predicted,13 but itshows the same trend.

The rate Xdv has contributionsfrom t\i collisions with both D2 andDT, so that Xdv = CA*n-d +

•Quoted errors reflect statistical uncertainly Alurther t 3% systematic uncertainty arises mainlyIrom the uncertainty in neutron detection elliciency

••Including a three body transler mechanism givesvalues ot Ots'nat vary more drastically and henceworsen the discrepancy (see Ret 11)

17<5

150

125

\ 100CD

o

* 7 5

50

25

nu

•

] 0.2

* C, = 0.5, SOOK

, C, 3 0.5. 450K

»Y C, = 0.5,

IS

0.4 0.6 0.8 1Density 4>

ct

ctr

" T T <

I i

.0 1.2

-= 0.5.

= 0.3.

-

= 0.7,

< 125K

0.08,125K

1.4

5 2378

FIGURE 2. Dependence ol the normalized cycling rate Xc on the density (p ol the dt

mixture The data presented here and below may change slightly upon lurther data

analysis

143

RESEARCH


TABLE I Fitted Contributions to the dfn Formation Ratea (in units of 106s~'that Xdtll = Cd[A.y,j,.d + X^-dV] + C^\C^,(p is fixed at zero].

. We assume

7(K) t-d

<130300

400-500

206 ± 29306 ± 43347 ±52

450 ± 50287 ±67275 ± 120

26 ± 692 ± 19

225 ±21aQuoted errors retlecl statistical uncertainty A lurther 13* systematic uncertainty arises mainly Irom Iheuncertainty in neutron detection elticiency

evidence of significant resonant dt\xformation via three-body collisions.

Menshikov and Ponomarev14 haverecently discussed a mechanism forthree-body resonant molecular for-mation—for example, t\i + D2 + D2

We write \dVr.x = X%-x + X&-&the

superscripts indicating the power of(p appearing in the observed (ratherthan normalized) dt\i formationrates. A global fit with all four termspresent shows that the A.^_, valuesare consistent with zero. Fitting withX^_, constrained to be zero gives thevalues shown in Table I and theKtn-Aty) for T< 130 K shown inFig. 3. We conclude that our datashow a strong linear (p dependencefor (normalized) Kdni-d, but not forl-aty.-,. The large values of K%-d are

singlet t\i + D2 collisions are special,in having their strongest resonancesjust below threshold where they arenot accessible in two-bodycollisions.8 By absorbing somekinetic energy, the spectatormolecule (D2,DT, orT2) moves

1

•o

i-

1000

800

600

400

200

o

•

0.0 0.2

r l l

i 1 l

0.4 0.6 0.8

Density <t>

I

oc, =oc,=

.c| =nc, =oC, =vc, =

1.0

-

0.30.40.5

o.e0.70.80.9

i

1.2

5 8182

FIGURE 3 Density dependence of the normalized molecular-lormation rate \mT < 130 K, assuming that A , ^ - , is density independent The solid line is a lit to the data(see Table I)

144

RESEARCH


these strong resonances abovethreshold, allowing them to con-tribute to molecular formation.

We turn now to the mechanisms ofmuon loss from the catalysis cycle.The muon may be captured and retained by a helium nucleussynthesized during dt\i, dd\n, or tt[i.fusion, with sticking probabilities Q)s,0)d, and (o,, respectively. The muonmay also be scavenged by 3He in-troduced by tritium decay (normallyCHe <C 0.01). The total muon-lossprobability per cycle can be written

as1.5

Xd,C,+

X

of(2)

where Xddti and X,v are the rates fordd\i and tt\i molecular formation,A.JH,. and X.,Ht. are the rates for transferto JHe from the c/u. and t\i groundstates, and (oHt. is the probability forinitial capture by He. The atf is thenthe effective sticking probability forthe dt\i fusion reaction.

It follows from Eq. (2) that dd\ifusion shows up in our experiment as'an increase in w for low-C, targets,permitting us to evaluate the productA.ddMcod at different temperatures. Be-cause corf has been measured inde-pendently,* we are able to extract

Xdd]i as a function of temperature, asshown in Fig. 4. Our results agreewell with the room-temperaturemeasurement of Xddtl of Balinet al.15

and, except for normalization, withearlier data15 over the range from 50to 400 K. Similarly, assuming that theobserved temperature dependenceof w for high- C, targets is due to thetemperature dependence of X,,m, weevaluate the corresponding productfor tt\i fusion, X(ni(0,= (0.4 ± 0.1) X106 s~\ Muon losses resulting fromscavenging by 3He are evaluated bynoting the increase in tv with time as3He builds up from tritium decay.

Subtracting from w the contribu-tions discussed above yields (tof,which depends on density andtritium fraction, as shown in Fig. 5.The striking variation with <p and C,was completely unexpected. Further-more, the observed value of ta'£, assmall as 0.3% and still decreasing

<ntoo

3 .• o

3.0

2.5

2.0

1.5

1.0

0.5

(

•

•

T 1

• / t

3 100

t

i

t!\n

X

1

200

A - T - " f I,r' I i i

* Balln et al. 1934• 1960-1979 data

t1

* Present experiment

300 400 500Temperature (K)

600

•

•

700

S2823

•For earlier measurements ol Xaail, see Ret 1 5

FIGURE 4 Temperature dependence ol the ddfi lormation rate XMfI (using(od = 0 122 from Ret. 15), trom data with C, < 13%, The solid line is a theoretical m(Ref 7) to earlier dala (circles); renormalization yields the dashed curve

145


2.5

£ 2.0

jos

4w

I 1981 Theory-I

j. 8 1985 Theory

O.I 0.2 0.3 0.4 0.5 0.6 0.7 0.8

S 337S

F I G ' J K E o Dependence ot (o|"c

!O' C, < 0 3 T<"ie vir.correeled values aare aiso snovvn The data are consistentwith ' , cof = (23 ± 10) + (419 + 34)(pyT) tor q> < I 3

at high density, is much smallerthan the calculated value16 of 0.9% fora sticking accepted before the present experiment. (The calculatedsticking fraction is the product of theprobability that the muon is initiallycaptured by the recoiling-fusiona particle, (0° = 1.2%, with the con-ditional probability that the muon isnot subsequently stripped, 1 — R —0.75.) More-accurate calculations17 ofinitial sticking have very recently re-duced this estimate by 25 to 33%, butthe resulting values still significantlyexceed our high-density ©^re-sults.*

The variation of (of-^could comefrom events (1) preceding or (2) fol-lowing the nuclear fusion. Under(2), the most likely origin is themuon-stripping process. Althoughthe value of R is somewhat uncertain,it is not expected19 to have nearly asmuch dependence on (p or C, as im-plied by Fig. 5. Under (1), a certainfraction of the muons may be delayedafter molecular formation hjut-beforefusion, thus increasing oaf above asmall initial sticking value.f The dtp.system, initially formed in tfie ex-

ci ted/= l,i>= 1 state, needs tocascade via Auger transitions to a7 = 0 state for fusion to be rapid.Possibly this cascade may be facili-tated by electrons supplied by ioniza-tion induced by tritium decay.21 Thesensitivity to (p and C, could thencome from the ion-electron recom-bination process, whose rate isproportional to (p \J~C,. This modelalso encounters some difficulties.20

Clearly, further study is needed todetermine which, if either, of theseideas can explain the observed de-pendence of <af.

With the experimental cof'wellbelow predicted values, 300 or morefusions per muon might be possible.We have already detected an averagevalue of 160 ± 4 (statistical) ± 20(systematic) fusions per muon, re-leasing about 3 GeV of energy, in aliquefied dt target with C, = 0.3.

In summary, we have discoveredsome completely unexpected targetdensity dependences in both the dt\imolecular-formation rate A.rf((l_rf andthe effective sticking probability (nf.The former is presumably due tothree-body contributions to resonantmesomolecular formation. The ori-gin of the latter is much less clear.

•Ralelski and Muller have suggested that the energydependence ol the nuclear-absorption amplitudeleads to a small value ol the initial sticking (seeRel 18)

146


References

1. S. E.Jones et al., Physical Review Letters 51, 1757 (1983).

2. A. J. Caffrey et al., "Experimental Investigation of Muon-Catalyzed Fusionin High-Density Deuterium-Tritium Mixtures," Muon-Catalyzed FusionWorkshop, Jackson Hole, Wyoming, June 7-8, 1984, pp. 53-67; and A. N.Anderson, "Mnon Catalyzed Fusion Data Analysis," MuonCatalyzedFusion Workshop, Jackson Hole, Wyoming, June 7-8,1984, pp. 68-74.

3. W. H. Breunlichet al., Physical Review Letters 53,1137 (1984).

4. V. M. Bystritsky et al., Zhurnal Eksperimental'noi i Teoreticheskoi Fiziki80,1700 (1981) [Soviet Physics-JETP53,877 (1981)].

5. L. I. Ponomarev, Atomkernenergie Kerntechnik 43,175 (1983).

6. L. I. Menshikov and L. I. Ponomarev, Pis'ma Zburnal Eksperi mental'noi iTeoreticheskoi Fiziki 39,542 (1984) \JETP Letters 39,663 (1984)].

7. S.I. Vinitsky et al., Zhurnal Eksperimental 'noi i Teoreticheskoi Fiziki 74,849 (1978) [Soviet Physics-JETP 4,1,444 (1978)].

8. M. Leon, Physical Review Letters 52,605 (1984).

9. J. S. Cohen and R. L. Martin, Physical Review Letters 53,738 (1984).

10. J. S. Cohen and M. Leon, Physical Review Letters 55, 52 (1985).

11. L. I. Menshikov and L. I. Ponomarev, Pis'ma Zhurnal Eksperimental'noi iTeoreticheskoi Fiziki 42,12 (1985) [Soviet Physics-JETP 42,13 (1985)].

12. K. A.Anioletal.,P/!7)'A-;c«//?ec/eH'/128, 2684 (1983).

13. A. V. Matveenkoand L. I. Ponomarev, ZhurnalEksperimental'noi iTeoreticheskoi Fiziki 59, 1593 (1970) [Soviet Physics-JETP 32,871(1971)].

14. L. I. Menshikov and L. I. Ponomarev, "Quasi-Resonant Formation of dt\iMesic Molecules in Triple Collisions" (submitted to Physics Letters B).

147


15. D. V. Balin et al., Pis'ma Zhurnal Eksperimental'noi i TeoreticheskoiFiziki 40,318 (1984) \JETPLetters 40,1112 (1984)], and referencestherein.

16. S. S. Gershteinet al., Zhurnal Eksperimental'noi iTeoreticheskoi Fiziki80,1690 (1981) [Soviet PhysicsJETP 55, S12 (1981)]; and L. Bracci and G.Fiorentini, Nuclear Physics A364,383 (1981).

17. D. Ceperley and B.J. Alder, Physical Review A 31,1999 (1985); and L. N.Bogdanova et al.,J1NR preprint E4-85-425, Dubna, USSR (1985).

18. J. Rafelski and B. Miiller, Physics Letters 164B, 223 (1985).

19. L. I. Menshikovand L. I. Ponomarev (to be published in Pis'ma ZhurnalEksperimental 'noi i Teoreticheskoi Fiziki).

20. J. S. Cohen and M. Leon, "Target Dependence of the Effective StickingProbability in Muon Catalyzed tff Fusion," Physical Review A 33,1437(1986).

21. P. C. Souers, E. M. Fearon, and R. T. Tsugawa, Journal of Vacuum Scienceand Technology A 3,29 (1985).

148

RESEARCHMaterials Science

MATERIALS SCIENCE

EXPERIMENT 842 SMC

Muon-Spln-Relaxation and Knight-Shift Studies of Itinerant Magnetsand Heavy-Fermion Materials

_os A.an'os ' ». OK. auiorvi at. ol

Spokesmen: D. W. Cooke and R. H. Hellnet (LosAlamos) and D. E. MacLaughlin (Univ. ofCalifornia. Riverside)

Introduction

Heavy Fermions. The focus ofExp. 8-J2 during the hist year hasbeen on measurements of theKnight-shift and zero-field relaxationrate in the heavy-fermion (HF)materials U^Tiv^ei, (.v= 0 00 and0.033) and UPt3. These materialsbelong to a larger class of heavy-elec-tron systems (including rare earihcompounds) that exhibit a number offascinating new properties,1 a few ofwhich are mentioned here.

1. HF materials possess a largelow-temperature susceptibility(X) and a large linear coeffi-cient of electronic specific heat(y), indicating an effective massof ~ 200 me, where me is thefree-electron mass. Curiously,the Wilson ratio (~%/y), whichis identically 1 for free elec-trons, is also — 1 for the heaviestHF systems.

2. At high temperatures most ofthe HF materials exhibit aCurie-law susceptibility with anonintegral number of Bohrmagnetons, suggesting itiner-ant magnetism.

3. By contrast, the total entropyper uranium atom is large(S/R ~- S«2 in UBe13), suggest-ing highly localized electronicexcitations.

4. "Clean" HF systems have a resistivity that is relatively smallnear T= 0 and that increaseswith increasing temperature, in-dicating the formation of acoherent electronic state in-volving hybridized/and con-duction-band electrons.

These HF properties seem related tothose of the single-impurity Kondoand mixed-valence systems, andsingle-impurity models are oftenused as a starting point for theories ofheavy-electron materials." The majorchallenge is to understand what newphysics is required in the HI7 state.

In addition to having unusual nor-mal-state properties, three HF sys-tems (CeCu,,Si2, UPt,, UBe13, and re-lated compounds) undergo super-conducting transitions that areunique in themselves. Because thediscontinuity in the specific heat atTc is comparable to that of the elec-tronic specific heat, it is believed thatthe heavy electrons themselves be-come superconducting and thus aredelocalized at low temperatures. Inconventional BCS superconductorsthe energy gap is only weaklyanisotropic-, therefore, transport,specific heat, and spin-relaxationmeasurements are exponentially ac-tivated below Tc. By contrast, HFsuperconductors exhibit power-law(~ V) behaviors3 5 below Tc, in-dicating a finite quasiparticle den-sity of states at the Fermi level even atT= 0; that is, the gap vanishes incertain regions of the Fermi surface.In analogy with 3He, one suspectsthat HF superconductors may exhibitboth unconventional pairing and,further, that the superconducting in-teraction is purely electronic ratherthan electron-phonon in nature. The-ories of HF superconductivity arecomplicated by a presumably strongspin-orbit interaction, band-structureeffects, and strong coupling 2 Regarding the last point, the characteristicenergy (kT0) for the onset cf the HF

150

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Materials Science

state is in the range from 10 to 100 K,so that Tc/Ta > Kr-andBoA, - 1,where 0o is the Debeye temperature.In normal metals the Fermi temperature TF is large, so that Tj'7e< i0~'

Muon-Spin Relaxation (fiSR) as aProbe of the HF State. Measurementsof the muon Knight shift allow amicroscopic determination of the lo-cal-spin susceptibility x and thus arean excellent probe of both the normal (xn) and superconducting (x.,>properties of the HF:; . e . In thesuperconducting state, for example,X is sensitive to the type of spin pairing present.6 For an even-parity(BCS) state, one has spin-singletpairing, and thus xs( T= 0) vanishesin the absence of spin-orbit coupling.For odd-parity spin triplet superconductivity,x.,(0) = x« (as inanisotropic^He — <4),orxs(0) < x«(as in isotropic3He — B). It is alsoknown that, for3He, strong Fermi-liquid corrections' reduce xs(0).Below, we discuss our measurementsof the Knight shift in U^Th^^e,}.Measurements on UPt3 are in progress.

In addition to probing the spinsusceptibility, muon-spin relaxation(|j.SR) is a sensitive tool to measurelocal magnetic field distributions andcan therefore be used to detect theonset of magnetic order. Zero-field|iSR was reported last year in UPt3;this year these studies have been ex-tended to L

Sample Materials andExperimental Technique

The samples were prepared byj. L.Smith (Los Alamos, Group MST-5).UBei3 exhibits a superconductingtransition at Tc ~ 0.86 K, as de-termined for our samples by acsusceptibility. Ui_v.ThABei,shows"two superconducting transitions for0.02 < .v< 0.05. For x= 0.033,Tc ^ 0.60 and 0.40 K. Ultrasound at-tenuation measurements have beeninterpreted9 in terms of an itinerantantiferromagnetism (AFM) transitionthat sets in below Tc. Nuclear mag-netic resonance (NMR) measure-ments5 have not detected such a tran-sition, however, and place an upperlimit of —0.01 Bohr magnetons forany possible magnetism.

The data were collected with theLAMPF |iSR spectrometer using 80MeV/c-momentum backward-decaymuons and applied transverse fieldsH between 0 and 5000 Oe. In thezero-field configuration the field atthe sample was zeroed to within10 mOe using earth coils. The (iSRdilution refrigerator10 was used forthe temperature range from 0.33 to3 K, and a conventional helitroncryostat was used for 7"> 3 K.

The |iSR time histograms were collected over the time range of 8 to12 us, depending on the experiment,and the Knight-shift spectra wereanalyzed in both time and frequency(Fourier transform) domains. A stan-dard copper sample at room tempera-ture was used as an absolute fre-quency standard, and copper runs

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Matenais Science

were usually taken before and afterruns on U ^ T h ^ e , , (copper has ameasured11 Knight shift of+60 ppm).In addition, the field stability duringeach run was monitored with an NMRprobe located near, but outside, thevacuum jacket of the cryostat. Theshunt voltage for the magnet powersupply was also monitored duringeach run. Nonlinearities and drifts inthe time-to-amplitude and analog-todigital converters used to histogramthe time spectra were monitoredbefore and after each data run. As aresult of these checks, systematic uncertainties in the measured absolutefrequency shifts were less than 1:10"'in the frequency range of interest,about 65 MHz. The statistical uncer-r 'inties were in the range fn,m 200 to400 ppm.

In transverse field a two line fre-quency spectrum was observed, oneline-shifted and one unshifted. It wasdetermined in auxiliary experimentsthat the unshifted line was duelargely to muon stops in the cryostat.At high transverse magnetic fields themomentum spread for tfc" muonsentering the sample -egion is suchthat some muons miss or are scat-tered from the sample because of dif-fering radii of curvature in the ap-plied field. This problem should becompletely eliminated next yearwhen the spin rotator is installed,because the beam will enter the spectrometer parallel to the field axis.

In addition to the frequencycalibrations, the Knight-shift datamust be corrected for demagnetiza-tion effects in both the normal andthe superconducting states. In the

normal state, one has for an ellipsoidal sample

K{=Kl - 4 7 t x ; ( l / 3 - n>) (1)

where K{ and K1, are the observedand intrinsic shifts, respectively, %' isthe bulk susceptibility, and »;is thedemagnetization factor (n = 1/3 for asphere). The superscript /"s refer tothe Cartesian coordinates of the el-lipsoidal axes x, y, and z. Our sam-ples roughly approximate ellipsoids,so that by using the measured xbulk

and approximating n we find that47rx(l/3 — n)< 10"4 in dimension-less units (UBe13 is a cubic material,

In the superconducting state adiamagnetic shift is produced due tocirculating superconducting cur-rents. The effect of this is to alwaysreduce the measured Knight shift;however, a quantitative estimate ofthis shift can only be made if themagnetization in the superconduct-ing state has been measured. To dateno such experiments have been pub-lished for U,_tThrBe13. The correc-tion depends on the sample shape, asin the normal state. These effects arediscussed further under Results.

Finally, we note that the intrinsicKnight shift itself may be anisotropic,either because of an anisotropic localsusceptibility (produced by lattice orcrystal-field structure, for example)or because of an anisotropic u+ ioninteraction, such as for dipolar cou-pling. For our preliminary analysis,we ignore the former, noting theUBen is a cubic material.

152


Results

Zero-Field Studies. The zero fieldlinewidth in UBe,3 for 0.3 K < T<10 K was temperature independent,with a value of o ~ 0.20 us"1. Wehave performed lattice-sum calcula-tions for nuclear dipolar broadening,assuming several sites, and find thatthe calculations are consistent withthe |i+ occupying a single site of oc-tahedral symmetry in the UBeI3 lat-tice. For the .v= 0.033 sample,o = 0.23 us"' for 0.33 < T< 0.7 K, asshown in Fig. 1. The origin of theslightly higher value for.v= 0.033 isnot known (thorium is mono-isotropic with no nuclear moment).It may be that the addition of a fewper cent thorium causes a slight shiftin the u+ equilibrium site position.

Knight Shifts. An analysis of the u+

Knight shifts is shown in Figs. 2 and3. Several results are apparent:(1) the shift is large and negative;(2) the shift tracks our measuredsusceptibilities for 4 < 7*< 100 K, butdeviates for T> 100 K; and (3) thereis a pronounced temperature de-pendence of the shift in the super-conducting state for.v= 0.00 but notfor .Y= 0.033. We discuss these re-sults in turn.

The large (>0.l%) Knight shiftmeans that all the corrections to theraw data in the normal state are of theorder of 10% or less. Thus we feelconfident that we have measured Kreasonably well. (The error barsshown in the figures are statistical.)The negative value is probably due tocore-polarization effects produced bydifferent radial dependences in the

?o.

1.

1

0

1

0

g0.

-

, T3 0.4

i

0.5 0TEMPERATURE T

T.600

Th0Q 33Be13

-

0.7 0.a

FIGURE 1 Temperature dependence ol the zero-field | i + Gaussian relaxation rate Arelative to the value 0 23 ± 0 03 |is~' at T= 0 7 K The transition temperatures Tc]

(superconducting) and Tc2 are indicated by arrows An upper bound ol —0 1 Oe isplaced by these data on any increase in | i + local field between 0 3 K and Tc2

0.0

X

- 0 . 1 —

-0.2

-0.3

-0.4

U 1 . x T h 1 B e 1 3Ho = 5 kOe• : 1 - 0

X: z - 0.033

10 15SUSCEPTIBILITY x (10 emu/mole)

F!GURE 2 Dependence ot ( i + Knigh'. shift K^ on bulk paramagnetic susceptibility % inUi_»Th,Be,3 x = 0 and 0 033, applied field Ho = 5 kOe Temperature is an implicitvariable The straight line is a least-squares fit to the data for % >; 8 X 10~3 emu/mole,and yields a hyperfme field Hhl = — 1 84 + 0 13 kOe/(xe

153

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Materials Science

spin-up and spin-down densities atthe n+ site. Negative n+ shifts havebeen seen in other materials—palladium, for example."Although the diamagnetic correc-tions in the superconducting statehave not been made, we note that,because they must be negative, theincreasingly positive Knight shiftbelow Tc in UBe13 must be intrinsicand thus the diamagnetic correctionsare small. Moreover, both specimens(JC= 0 and x= 0.033) are extreme

0.0

-0.1

-0.2

-0.3

-0.4

1S

I | I I I I I 11 I I I I I I t II

I *0.1 1 10

TEMPERATURE (K)100

FIGURE 3

(a) Temperature dependence z1- the |i fKnight-shift K,, between 0 3 and 300 KinU,-,Th,Be,3 x = OandO 033, applied field Ho = 5 kOe. The superconductingtransition temperatures are indicated by arrows, labeled by the symbols inparentheses

(b) Temperature dependence of \i+ Gaussian Nnewidth a, conditions are the sameas in(a).

type II superconductors for whichmixed-state diamagnetism is small,so that the differences seen in theKnight shifts in these two materialsbelow Tc are intrinsic.

The temperature dependence of K,can be modeled as

/ f ((n=ax, + Pxor(,+ 8X / (n , (2)

where X\ is the contribution from s-like electrons, %arb is an orbital term(analogous to the Van Vleck suscep-tibility) , and X/( T) is due to theheavy (5/like) electrons. Both %l and%orb are taken to be temperature-in-dependent. The fact that Kt (T)tracks the bulk susceptibility forT< 100 K (Xbuik> 8 emu/mole)means that we are sampling the heavyelectrons in this regime. From theslope of the Xbu/* versus Kt(T), weobtain a hyperfine field of—1.84 +0.13 kOe/nfl. We do not understand,however, why K, (T) breaks awayfrom Xto/* (T) at the highertemperatures (%(,„«,<8 emu/mole).A plot of Xdurt versus \/T reveals atemperature-independent contribu-tion of =: 1 X 10~3 emu/mole. Wenote that a similar value wasobtained10 years ago, from27Al NMRon UAl2, and associated with xor(,.

154


Discussion

Zero-Field Relaxation. In UBeB

the magnitude of the linewidthoallows a determination of the likely |i+

site, as discussed above. The fact thatthe width is independent of tempera-ture means ihat the u+ is stationary. InIWrho.ojjBe,, the absence wf achange in a down to T/Ta — 0.83allows one to set an upper bound tothe magnitude of any quasi-static lo-cal field produced by itinerant anti-ferromagnetism (AFM). A com-mensurate AFM order of wavelengthequal to the muon site spacing couldcancel the local field by symmetry,but an ordinary commensurate spin-densiiy wave requires both aparticular balance of electron/atomratio with band structure12 and aperfectly symmetric u.+ site. Thesecannot be completely ruled out, butseem unlikely a priori. In theabsence of such cancellation we findthat any AFM moment must be lessthan 1CT1 \iB. This limit is about 100times lower than the upper bound5

setby'BeNMR.

Knight Shirts. The most unam-biguous and important fact derivedfrom these data is that the two super-conducting states in the (U,Th)BeB

system (one for x = 0 and one for

.v= 0.033) seem to be qualitativelydifferent, as reflected in the differenttemperature dependences of Aj,below Tc. This fact leads directly tothe conclusion that the supercon-ducting-order parameter in the(U,Th)Beu system is not likely to beof the conventional, isotropic BCStype, which does not allow two distinct superfluid phases.

We now address the temperaturedependence of the Knight shift inpure UBe,3. The earliest NMR Knightshifts6 in the BCS superconductorsaluminum and mercury showedX,(0)/x» - 0andx s (0) /x n « 0.7 to0.8, respectively, the difference be-ing attributed to a large spin-orbitinteraction in mercury, coupled withsamples whose geometricaldimensions were smaller than thesuperconducting coherence length.Thus, Cooper pairs reflected from thesample surfaces had their spinsflipped by the spin-orbit interaction,and so the zero-temperature suscep-tibility remained large. Because spin-orbit coupling is strong in uranium-derived wave functions, spin-orbitscattering would be expected to in-crease Xs(0) substantially, if this ma-terial exhibits conventional BCS pair-ing. This was not observed, whichsuggests unconventional pairing.

155

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Materials Science

References

1. G R. Stewart, Reviews of Modern Physics 56,755 (1984).

2. P. A. Lee, T. M. Rice,J. W. Serene, L.J. Shan, andj. W. Wilkins, "Theoriesof Heavy-Electron Systems" (to be published in Comments on Solid StatePhysics).

3. D. Jaccard, J. Flouquet, P. Lejay, and J. L. Tholence,/o»r«fl/ ofAppliedPhysics 57,3062 (1985).

4. H. R. Ottetal., Physical Review Letters 52,1915 (1984).

5. D. E. MacLaughlin, C. Tien, W. C. Clark, M. D. Lan, Z. Fisk,J. L. Smith, andH. R. Ott, Physical Review Letters 53,1833 (1984).

6. R. Meservey and B. B. Schwartz, in Superconductivity, R. D. Parks, Ed.(Marcel Dekker, Inc., New York, 1969), p. 118; and D. E. MacLaughlin,Solid State Physics 31,1 (1976).

7. A. J. Leggett, Revieiv of Modern Physics 47,331 (1975).

8. H. R. Ott, H. Rudigier, Z. Fisk, andj. L. Smith, Physical Revieiv B 31,1651(1985).

9. B. Batlogg, D. Bishop, B. Golding, C. M. Varma, Z. Fisk, J. L. Smith, and H.R. Ott, Physical Review Letters 55,1319 (1985).

10. D. W. Cooke,J. K. Hoffer, M. Maez, W. A. Steyert, and R. H. Heffner, "ADilution Refrigerator for a Muon-Spin Relaxation Experiment" (to bepublished in Revieiv of Scientific Instruments).

11. A. Schenck, HelveticaPhysicaActa 54,471 (1981).

12. W. C. Koehler, R. M. Moon, A. L. Trego, and A. R. Mackintosh, PhysicalReview 151,405 (1966).

156


The results of muonspin-relaxa-tion (u.SR) experiments in the magnetic oxides, including oxide spinglasses, have been particularly fruitful this past year, resulting in severalrefereed publications and con-ference contributions. The effort hasbeen directed into three main areas:

1. (ASR study of the dynamics ofthe magnetic environment inmagnetite (Fe,O.,) in the ternperature region near 247 Kwhere the reported anomaloustransition in the local muonfield and depolarization rate oc-curs,

2. a new experimental study onthe oxide spin-glass Fe,TiO,(pseudobrookite), and

3. further theoretical work on themuon site in karelionite(V2Oj).

Details of these investigations aregiven below. These show clearly thatthe muon provides a sensitive probeof the dynamic processes in magneticmaterials on the atomic scale andthat, particularly in magnetite, it isone of the most sensitive experimen-tal tools available.

Magnetite (Fe3O4)

As described in detail in our latestpublications,12 the Mott-Wigner glassstate in Fe3O4 has been firmly estab-lished for temperatures above theVerwey transition (125 K). Much ofthe work this year was devoted to astudy of the muon hyperfine fieldand depolarization anomaly at 247 K.The origin of this anomaly has beenof considerable interest since its discovery3 by nSR measurements.

We have now come much closer toan understanding of this effect. Datataken over a year ago4 showed thatthe dynamical fluctuation of the magnetic environment is slower than themuon precession frequency below247 K, and faster above that temperature (see also the LAMPF ProgressReport for 1984, Ref. 4). This resultprompted additional external-fieldmeasurements, which wereperformed this year.

Figure 1 shows the results of theapplication of a field of 2500 and720 Oe as the temperature was variedacross the anomaly at 247 K. As canbe seen for Bes, ||<110> above 247 K,only one frequency (that is, one mag-netic muon site) is observed,whereas below this temperature twofrequencies (sites) are observed.

EXPERIMENTS 639 and854 — SMC

Muon-Spln Relaxation (fiSR) mSelect Magnetic Oxides and OxideSpin Glasses

Texas Tech Univ., Univ. ol Wyoming, LosAlamos, Technical Univ. ol Eindhovenm The Netherlands

Spokesmen (Exp. 639): C. Boekema (Texas TechUniv.), A. B. Denison (Univ. ol Wyoming), andD. W. Cooke (Los Alamos)

Spokesmen (Exp. 854): C. Boekema and R. LLichti (Texas Tech Univ.) and D. W. Cooke(Los Alamos)

95

90

85

BO •

100

1*1Fe3q,, single crystal

— - Z S O O O e• 720 Oe —»

ZOO

T[K]

i

1

|

I1

-

•

300

70

65

60

X4

1"M

FIGURE 1. Temperature dependence lor the nSR signal at Bgxl = 720 and 2500 Oe(B9»J<110».

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130

120

110

100

JL 90

80

70

60

! 1 1

/

I1 1 1

1.0 2.0 3.0

B.xt

/

/

Fe304

singleB IIDext II205 K

i

4.0

[kOe]

i i i

/

f

-

crystal<IIO>^ II \J^

l i t

5.0 6.0 7.0

FIGURE 2 External field dependence ol the |iSR signal in Fe3O4 at 205 K Bex, isparallel to the (1 10) direction

The dependence on external-fieldstrength at a constant temperature(205 K) is shown in Fig. 2. Above thedemagnetization field (~200 Oe)the iron moments are parallel to theapplied-field direction. The slope ofthe field dependence (13.5 kHz/Oe)indicates that the effective localmuon fields are parallel to the ap-plied field. The interpretation ofthese results, along with the earliercross-relaxation work,4 is that a break-down of short-range (atomic-cluster)order occurs above 247 K. Two typesof magnetic sites exist below thistemperature that are correlated withthe characteristics of the short-rangeorder. New, selectively doped(nickel and zinc) crystals are cur-rently being investigated in hopes ofaltering the motion of the atomicclusters' range and, therefore, ofshifting or destroying the anomalyobserved at 247 K in pure magnetite.

Pseudobrookite (Fe2TiO5)

A new research direction beganthis year with the jiSR study of oxidespin glasses. Initial experimentswere conducted on modifiedpseudobrookite (Fe, 75Ti, 25O5)prepared by V. A. M. Brabers(Eindhoven). Zero-field measure-ments were made to obtain the asym-metry and depolarization rate as afunction of temperature. As observed

158

BESEABCH

Materials Science

from Fig. 3, the depolarization rateshows a marked increase at the glasstransition temperature ( = 45 K),withanother smaller increase near 8 K.The shape of the depolarization ver-sus temperature curve just above theglass transition can be used to com-pare two competing theories of spindynamics, namely the standardpower law5 versus the Vogel Fulcherlaw.6" The change in depolarizationrate near 8 K is associated with thesuggested onset8 of the transversespin ordering. Further analysis willdetermine the validity of this inter-pretation.

Karelionite (V2O3)

The main thrust this year of the|iSR results on V2O3 (see the LAMPFProgress Report, Ref. 4) has been theinterpretation of our previousmeasurements.910 The data showed aclear jump in the local field at themagnetic and metal-insulator transi-tion temperature ( T, ~ 134 K) forour oxygen-deficient sample. Be-cause of the electronic configurationof the vanadium ion, the source ofthe local magnetic field is mainly ofpoint-dipole origin from the V3+. Cal-culations based on dipole sums havebeen performed to search for andidentity the muonstopping site. The

original calculations9 found a set ofsites that satisfied the experimentalresults for the 15-MHz uSR signalwith respect to the magnitude anddirection of the local field when anexternal field was applied. However,in the original search, sites appearedto be missing, as deduced from ex-perimental asymmetries. Recentwork by Chan et al.10 indicated addi-tional sites, explaining the 0-MHz|iSR signal. Summarizing for V2O3,Bates muon sites, as well asRodriguez muon sites (similar tothose found in <x-Fe2O3), have beenfound. Comparing V2O3, Fe3O4, anda-Fe2O3 jiSR studies, we concludethat muon-oxygen bonding occurs ininsulating as well as (semi)metallicoxides.

'VI

1 '

t

0 6

0 5

0 4

OS

OZ

01

F e " 5 7

i0

V2A

1o

T

III 1

U 1. . . t

10

10

I

1fj

II.1 ."

T[K]

I

hir1

V.,

o

•

1I '

o . o •

1.0

0.5

1000

Ot

1;

FIGURE 3 Depolarization rate measured as a function of temperature forFeT T^TI-I 25O5. The open circles represent the fit with the standard power law (Re! 5),the solid circles, that for the Vogel -Fulcher law (Refs. 6 and 7).

159


References

1. C. Boekema, R. L. Lichti, K. C. B. Chan, V. A. B. Brabers.A. B. Denison, D.W. Cooke, R. H. Heffner, R. L. Hutson, and M. E. Schillaci, PhysicalReview B 55, 2\0 (1986).

2. N. F. Mott, Metal-Insulator Transitions (Taylor Francis, Ltd., London,1974).

3. C. Boekema, Philosophical Magazine B42,409 (1980).

4. C. Boekema, R. L. Lichti, V. A. M. Brabers, A. B. Denison, D. W. Cooke, R.H. Heffner, R. L. Hutson, M. Leon, and M. E. Schillaci, Physical Review B31,1233 (1985); and "Progress at LAMPF," Los Alamos National Labora-tory report LA-10429-PR (April 1985), pp. 105-108.

5. R. Rammel andj. Souletie, "Spin Glasses," in Magnetism of Metals andAlloys, M. Cyrot, Ed. (North Holland Publishing Co., Amsterdam, 1982),Chap. 4, pp. 379-486; R. H. Heffnei jt al. Journal ofApplied Physics 53,2174 (1982); and J. Uemuraet al., Physical Review B 31, 546 (1985).

6. J. L. Tholence, Solid State Communications 35, 113 (1980).

7. H. Vogel, Zeitschriftfuer Physik 22,645 (1921); and G. S. Fulcher,Journal of the American Ceramic Society 8, 339 (1925).

8. Y.YeshuranandH.Somplinsky, Physical Review B 31, 3191 (1985).

9. A. B. Denison, C. Boekema, R. L. Lichti, K. C. B. Chan, D. W. Cooke, R. H.Heffner, R. L. Hutson, M. Leon, and M. E. Schillaci Journal ofAppliedPhysics 57,3745 (1985).

10 . K. C. B. Chan, C. Boekema, R. L. Lichti, D. W. Cooke, M. E. Schillaci, andA. B. Denison, "Muon-SpinRotation Study of V2O3,Journal 0/AppliedPhysics 57(1), 3743 (1985).

160

RESEARCH

Malenals Science

A wide variety of magnetically dis-ordered materials exhibit twomagnetic transitions: ( D a fer-romagnetic transition at a Curie ternperature Tc and (2) a transition to aspin-glass state at a lower tempera-ture Tg. We have studied both thefreezing and the spin dynamics inone such system, /•V/I'ell,lwMn,,0<;, us-ing zero field muon spin relaxation(uSR). The free/ing processes havebeen considered in a previousrepon,' so we discuss here the recentimprovements in our analysis of zerofield data and the use of the ^SRdilution refrigerator, which have ledto a better understanding of the spindynamics near and below Tt.

Time dependent fluctuations ofthe impurity moments contribute tothe muon depolarization through themagnetic dipole coupling to themuon moment. The dynamic contribution to the depolarization domi-nates the observed relaxation at longtimes for T< TL. Above Tc there is noquasi-static field and the observedrelaxation is entirely dynamic in ori-gin. The resulting relaxation functionP(t) is usually assumed to be eitherexponential or root exponential,Pit) x exp[- (Xt)l/2]. We argue belowthat neither form adequately de-scribes our data, so we briefly reviewthe calculation of the depolarizationfunction in the case of no muon dif-fusion. More complete discussionshave been given by McHenry e( al.2

and by Seymour and Sholl.3

In the motional narrowing limit,which is appropriate here, a muon atsitey has an exponential depolariza-tion function

= exp . ( i )

where the sum is restricted to theoccupied impurity sites surroundingthe muon s i te / The overall depolarization function P( t) observedin a uSR experiment is an average ofthe Pj(t) overall muon sites. Be-cause the Pj (/) may depend stronglyo n / the average P(t) will in generalbe nonexponential. For dipolar orRKKYcoupling, \/Tx{rSj) can be ap-proximated3 by an angle-averaged re-laxation rate 1/7\(Y) = K/r6, where Kis a temperature-dependent quantitycontaining the impurity fluctuationtime and the coupling strength. Notethat any concentration dependenceobserved in K\s due to the concentra-tion dependence of the impuritydynamics. All direct concentrationdependence in the muon relaxationfunction has been removed throughthe sum in Eq. (1) and the averageover muon sites.

When 1/ 7", ( r) = K/r6, the averagerelaxation function is given by2'3

EXPERIMENT 941 —SMC

Muon-Spln-Relaxation Studies(nSR) of Disordered Spin Systems

Rice Univ , Los Alamos, Univ olCalifornia al Riveiside

Spokesmen: S. A. Dodds (Rice Univ.), R. H.Heflner (Los Alamos), and D, E. MacLaughlin(Univ. ol California, Riverside)

P(t)= ce xp(-tK/r6,)]

( 2 )

where c is the impurity concentra-tion and r, are the possible impuritysite locations relative to the muonsite. The general behavior of the relaxation function is determined by c

161


and by t0 = rl/K. The parameter r0 isthe minimum muon-impurity dis-tance, so ?o' is the maximum muonrelaxation rate from a single impurity.When c —- 1, the Pit) is exponentialat all times, but at the concentrationsof interest here, c < 0.1, the Pit) isexponential for / <§C t0 and root ex-ponential for / » t0. In practice, itmay be difficult to observe the ex-ponential region at low concentra-tion because very little depolariza-tion will occur for f < /„. The rootexponential will then be a good ap-proximation to the observable de-polarization function.

An explicit calculation of Kisstraightforward in the dipolar cou-pling case, yielding2

P(t) = exp-j i* p q e{-'/l0) - 1

K=l33(hyt,ys)2 (3)

where y^ and ys are the muon andimpurity gyromagnetic ratios, 5 is theimpurity spin, and xeff is an effectiveimpurity correlation time. The nu-merical factor arises from the angularaveraging of the dipolar coupling.

Equation (2) is clumsy to use forfitting data because evaluation of thelattice sum is lengthy. In the limit ofsmall concentrations it is convenientto use a continuum approximation,replacing the lattice sum by an integral to obtain2

, (4)

where p is the number density of hostsites. The quantity r0 is an innercutoff radius for evaluation of theintegral. In terms of theseparameters, the limiting root-ex-ponential rate is A. = (I67t3/9)p2c2#,obtained when r0 — 0. By taking r0 asan adjustable parameter, one can alsoapproximate the exact Pi t) for thecase where the near-neighbor sitesare excluded.

The muon-relaxation data aboveTc were initially fit with both ex-ponential and root-exponential func-tions. The resulting x2 per degree offreedom suggests a change from anexponential form at the highest tem-perature (low relaxation rate) to aroot-exponential form at lower tem-perature. Neither function fits the en-tire range well. The more generalform of Eq. (4) requires a two-param-eter fit to the data in a region wherethe relaxation function does not haveeither limiting form. The P( /) data atT= 10 K fulfill this requirement. Ac-cordingly, Pit) from Eq. (4) was fitto the data by adjusting AT and r0. Wefind that r0 /a0 = 0.72 ± 0.08, wherea0 is the palladium fee lattice param-eter. This value of r0 was then heldfixed for the fits at other tempera-tures. The resulting %2 values demon-strate that this procedure accuratelydescribes our depolarization data.

162

RESEARCH

Materials Science

Comparing the value of rQ

[deduced from fitting the data toEq. (4)] with the exact lattice-sumresults when various sites are ex-cluded, we infer that there is no contribution to P(t) from the interstitialsites nearest the impurities. In a nor-mal resonance experiment with alarge applied field, this might be dueto the shift of the muon resonancefrequency produced by the polarizedimpurity moment. The shift wouldalso entail a loss of signal amplituderelative to the pure host signal by afactor of (1 — c)" = 0.63, because thesix near-neighbor sites would notcontribute to the intensity of the ob-served signal. Here, the muon P( t) ismeasured in zeio field and the fullasymmetry is observed above Tc, sothis mechanism cannot be signifi-cant.

We suggest instead that the muonis physically excluded from the oc-tahedral interstitial sites nearest themanganese impurities. This could becaused by a contraction of the hostlattice around the manganese or by arepulsive muon-manganese interac-tion of electronic origin. X-ray latticeparameter measurements on a seriesof PdMn alloys containing 2 to 10%manganese do not show any signifi-cant deviation from the purepalladium lattice parameter, leadingus to infer that the effect is elec-tronic. Presumably, muons are alsoexcluded from near-neighbor sites inthe other PdMn alloys previouslystudied45 by nSR.

The spin-lattice-relaxation rateconstants K, obtained from fittingEq. (4) to the fWFeMn data with r0

fixed, are plotted in Fig. 1. Above Tc

the fits have the full muon asymmetry, and the whole time range isincluded in the fit. Below r c the initial damping from the quasi staticfields reduces the initial asymmetryfor the dynamic part to one-third, andonly the time range beyond the initial falloff is included in the fit.

Two additional data points(triangles) were taken in an appliedlongitudinal field. The significanceof these data is discussed below. Forcomparison, we have also reanalyzedearlier data4'5 on ferromagneticPdMn002 and on spin-glass PdMn007,using Eq. (4) with r0 = 0.72 aQ.These results, scaled by their respec-tive ordering temperatures, areplotted as the solid and dashed lines.Figure 1 also presents the tempera-ture dependence of the low-fre-quency (21. /-Hz) ac susceptibilityon the same PrfFeMn sample.

The onset of dynamic broadeningabove Tc is similar to that seen inferromagnetic PdMn, as shown bythe solid curve in Fig. 1.Furthermore, application of a longi-tudinal magnetic field strongly sup-presses the muon relaxation forT > Tc, in agreement with previousresults4 in ferromagnetic PdMn. Bycontrast, a field has only a modesteffect on muon relaxation in a spinglass.5 It seems reasonable to con-clude that the transition at Tc is to aferromagnetic state, as previously re-ported.6 It is not known why the

FIGURE 1.(a) Temperature dependence ot the

real (x') and imaginary (x") parts olthe low-field ac susceptibility ol thejiSR sample, showing Tg =* 1.9 Kfrom the peak of x "

(b) Temperature dependence of thezero-field muon spin-lattice relaxa-tion parameter (defined in the text),scaled by the palladium lattice pa-rameter. Here, Tc = 8.25 K, Iromthe peak of the nSR rate ^circlesrepresent the zero-applied field;triangles, the 1 -kOe longitudinalfield).

The solid line represents muon-relaxationrates in ferromagnetic Pd Mn0 02, withtemperatures scaled by Tc = 5.8 K(Ref, 4), The dashed line representsmuon-relaxation rates in spin-glassPdMn0 0? with temperatures scaled byT g = 5 . 0 K(Ref 5).

163

RESEARCHMaterials Sc

Curie temperature determined fromthe peak of the |iSR rate,Tc = (8.25 ± 0.1) K, is somewhatlower than the temperature of thepeak in x" or the inflection in %'.

The transition to the spin-glassstate is marked by the lower-temperature peak in / " and the falloff in x'•No comparable signal in the muonrelaxation exists, although the relaxa-tion rate gradually decreases belowTg and is much less sensitive to ap-plied fields near Tg than it is near Tc.A nonreentrant spin glass (forexam-ple, fWMno.o7) would display an in-crease in relaxation rate over a widetemperature range as T-* Tg fromabove (indicated by the dashed linein Fig. 1). The rate near Tg would besimilarly insensitive to appliedfields.5

In the temperature region betweenTc and Tg the relaxation-rate constantremains substantially elevated, incontrast to the ferromagnet where therate constant falls to immeasurablylow values at comparable reducedtemperatures. This indicates the con-tinued presence of slow fluctuationsin this temperature range. FromEq. (3) we can deduce effective cor-relation timesxejr— 10"'"to 10"" sfor these fluctuations. At the sametime, the lack of an increase of K/an

(Ref. 6) near 7 in PaTeMn impliesthat the ferromagnet to spin-glasstransition is not accompanied bycritical fluctuations in the frequencyrange 0) — 1010s"'probed by (iSR.The low-frequency spin fluctuationsof this reentrant system are thereforeunlike those of either a disorderedferromagnet or a spin glass.

References

1. "Progress at LAMPF," Los Alamos National Laboratory report LA-10429-PR(April 1985).

2. M. R.McHenry, B.G. Silbemagel,andJ. H.Wernick, Physical Review B 5,2958(1972).

3. E. F. W. Seymour and C. A. Sholl, Journal of Physics C: Solid State Physics18,4521 (1985).

4. S. A. Dodds, G. A. Gist, D. E. MacLaughlin, R. H. Heffner, M. Leon, M. E.Schillaci, G.J. Nieuwenhuys, andj. A. Mydosh, Physical Review B 28, 6209(1983).

5. R. H. Heffner, M. Leon, M. E. Schillaci, S. A. Dodds, G. A. Gist, D. E.McLaughlin.J. A. Mydosh, and G.J. Nieuwenhuys, Journal ofAppliedPhysics 55,1703(1984).

6. B. H. Verbeek, G.J. Nieuwenhuys, H. Stocker, andj. A. Mydosh, PhysicalReview Letters 40, 586 (1978).

164


Progress toward increasing theLAMPF muon spin relaxationcapabilities occurred in three area.s:(1) construction of an addition to theSMC West cave to provide space forthe permanent installation of the (iSRspectrometer and the muon-spin ro-tator, (2) construction of a muonspin rotator, and (3) continuing de-velopment studies of the unionbeam chopping system. These three-items will enable uSR experiments tobe done with more convenience andefficiency, at higher data rates, atlower temperatures, and with thinsamples.

During 1985. Group MP-7 con-structed an addition to the SMCWestcave to accommodate the uSR spec-trometer. 1 his improvement willgreatly enhance the the efficiency ofdoing uSR experiments by eliminat-ing the necessity of setting up anddismantling the spectrometer forevery run and by reducing theprobability of damage to fragile spec-trometer and cryogenics components:during moving, assembly, and dis-mantling of the experimental setup.

Plans in 1986 are to install and testa spin rotator that will give the capa-bility of rotating the muon spin 90 °before the muon enters the juSR sam-ple. A spin rotator will allow bothtransverse and longitudinal-fielduSR measurements to be donewithout turning the |iSR spectrom-eter magnet to orient the magneticfield appropriately for each type ofmeasurement. Group MP 13 has refurbished a 3 m long particle

separator to be used as the rotatorand has undertaken the procurementof power supplies that will providehigh voltage to ihe separator.

The successful muon beam-chop-ping feasibility studies carried out in1984, using rudimentary electronics,were followed this year by test runsusing a more complete sytem comprising newly designed high voltageand control electronics and a beam-line component layout closely ap-proximating the configuration to beused for the final installation. Thechopper control electronics workedas expected and the high-voltage sys-tem switched the beam on and offfaster and operated with much higherreliability than the old system.

To transport the beam to the [iSRspectrometer in the new SMC-Westcave addition, beam-line compo-nents were arranged so that the muonbeam, after exiting QM21 in the westcave, passes through the beam chop-per box containing the crossed elec-tric and magnetic fields and into a20° bending magnet. It is then re-focused by a quadrupole doublet toform a spot at the |i.SR sample po-sition in the spectrometer. A driftspace between the doublet and thespectrometer will eventually be occupied by the spin rotator.

Improvements to the Muon-Spln-Relaxation (nSR) ExperimentalFacilityR L Hutson (Los Alamos)

165

RESEARCH

Materials Science

EXPERIMENT 787 — Biomed

Miion Channeling lor Solid-statePhysics Information

Los Alamos, Max Planck Institute atStuttgart. Texas Tech Umv , TechnicalUniv of Munich, Umv ot Mississippi

Spokesmen; G. Flik (Max Planck Institute atStuttgart), K. Maier (Max Planck Institute atStuttgart), and M. Paciotti (Los Alamos)

Participants: C. Boekema, J. Bradbury, W. Cooke,H. Daniel. G. Flik. ft Heffner. M. Leon. K.Maier, M. Paciotti, J. Reidy, H. Rempp. andM. Schillaci

The most interesting muon-chan-neling results obtained at LAMPFcame from light-on/light-off experi-ments in germanium and galliumarsenide along the (110) direction. Alarge concentration of excess-chargecarriers was produced in these high-quality single crystals !_>/ directingthe radiation from a tungsten lamponto the sample surface. Taking ad-vantage of the structure of the LAMPFpion beam (pulse repetition period8.3 ms, pulse length S750 (is), thelight was chopped so that each pulseoverlapped alternate pion pulsesstriking the crystal. This resulted in ahigh carrier concentration when thelight was on and, because of rapidsurface and bulk recombination, anintrinsic concentration when thelight was off. This technique allowedus to (1) reduce the heat load on thesample, (2) observe the effects of dif-ferent carrier concentrations at thesame sample temperature, and(3) minimize the effects of any smallshift in crystal orientation or drifts inelectronics with time.

Most of the photons produced bythe lamp (T= 3400 K) and trans-mitted through the Lucite light guidehave energies exceeding thegermanium (Eg=0.6l eV) and gal-lium arsenide (Eg= 1.43 eV) bandgaps. Upon illumination, the carriersare produced at the surface within adepth a ~ 1 p (a being the absorp-tion coefficient), whereupon theyrapidly diffuse into the bulk. For typi-cal bulk recombination times, thisdistance far exceeds the 50-u.m depth

from which the channeled muonsemanate. Thus, within this depth thecarrier concentration resulting fromillumination is constant, a typicalvalue being 1015 cm"3 for germanium.

In Fig. 1 we show radial averagesof the relative muon yield forgermanium as a function of the angle\|/ measured with respect to the ( l 10)direction. Data are presented forlight-on and light-off conditions attwo different temperatures. Theradial average is obtained by dividingthe two-dimensional channeling databy a random spectrum—that is, oneobtained by putting a scattering foilbetween the sample and the muondetector—and subsequently averag-ing the relative number of muons thatlie within a fixed radius of the center.By increasing this radius, one obtainsi radial average distribution (chan-neling profile) of the channeledmuons.

At 100 K there are striking dif-ferences between the muon-channel-ing profiles taken with light off andlight on [compare Figs. 1 (a) andl(b)]. For example, with light off wesee both a center peak (that is,\|> = 0 °) and an off-center one(\|f = 0.22 °), whereas with light onwe observe only an off-center peak(y = 0.1°). At 200 K[see Figs. l(c)and 1 (d)], we do not observe anyappreciable difference (withinstatist'eal error) between light-offand light-on conditions. Each profileexhibits a center peak with hints ofpossible off-center peaks. Thus, weconclude that the differences in themuon-channeling profiles observedat 100 K can be attributed *o the

166

RESEARCH

Materials Science

occupation of different pion sites, re-sulting from an increased carrier concentration during the light-on con-dition. Furthermore, we note thatpion sites at 200 K are different fromthose at 100 K and are essentially un-affected by light.

Figures 2(a) and 2(b) contrast thelight-off/light-on differences in themuonchanneling profiles of galliumarsenide taken at room temperature.

Qualitatively, these results aresimilar to those of germanium at100 K[Figs. l(a) and l(b)], that is,we observe both a center and an off-center peak for light off, but only anoff-center peak for light on. Theseresults are consistent with our con-clusion that for some temperatures apion site change occurs when thefree-carrier concentration is in-creased (lighion).

130

120

HO

§ IOO

| , 3 0

I120

110

100

(a)Ge<IIO>Light offT« I00K

H Light offT*200K

I I I I

(b)Ge<IIO>Light onT»l00K -

(d) Ge<IIO>Light onT=200K

H(

0 O.I 0.2 0.3 0.4 0.5 0 O.I 0.2 0.3 0.4 0.5

FIGURE 1 Radial averages ol relative muon yields lor germanium.

167


» 130

co2 120o>

| "°

100

-

1

\

- * *

1 1

1 1 1 ' '

(a) GoAs<IIO>Light offRoom Temp.

i i i , .

-

1

(b)

1 \\\\

i i

i i

GaAs<IIO>Light onRoom Temp.

-

i i

0 O.I 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4Y(deg)

FIGURE 2 Radial averages of relative muon yields for gallium arsenide

For a qualitative interpretation ofthe data in terms of specific site oc-cupancy we refer to Fig. 3, which represents the projection of a diamond-type lattice onto a (110) plane. Thepositions of hexagonal (//) andtetrahedral (T) sites are shown withrespect to the (110) channel. Othersites of interest are bond-centered(BC) and(lll)aniibond (AB) sites.

Figures 1 and 2 illustrate muon-flux enhancement exclusively, thatis, channeling rather than blocking,so one can immediately excludesubstitutional sites as candidates forpossible pion locations. Moreover,channeling theory1 predicts that pionsites located in or very near a channelcenter produce muonchanneling

peaks centered at i|/ = 0, whereas off-center sites yield off-center (\|/ < 0)peaks. Unfortunately, theoretical ef-forts have not shown definitively thatone can in fact resolve the Tand H\sites in a muon-channeling experi-ment. Thus, we cannot currentlymake an unambiguous correlation ofobserved channeling peaks withspecific pion sites based on the dataalong (110) directions alone. For atrue site determination, we need ad-ditional data along (100) and/or( i l l ) directions, therefore, we dis-cuss the two different possibilitiesthat are left.

If /-/-site occupancy is preferredwhen the light is off, the center peakcould be due '•? a pion residing at H\whereas the off-center peak could beattributed to H2H5 occupancy. For

168


light on, the pion would preferen-tially occupy the Tsite. This interpretation seems plausible i'.»ced onthe angular position of the off-centerpeaks for both germanium and galHum arsenide during light on. Thatis, we note that the off-center peakoccurs at a smaller angle during lighton than during light off. One must besomewhat careful with this conelusion, however, because it mightbe possible to generate an off centerpeak [as shown in Figs. 1 (b)and2(b)] by appropriately weighting twopeaks such as those shown inFigs. Ha) and 2(a). This fact, cou-pled with our lack of knowledge re-garding 7"- and //-site resolution, suggests a second equally plausible in-terpretation of the observed muon-channeling profiles.

The center peaks observed inFigs. l(a) and2(a) are associatedwith pions occupying H\ and/orT sites, whereas the off-center peaksrepresent AB site occupancy. Withlight on [Figs. Kb) and2(b)],abrgerportion of the pions occupy AB sitesthan //and/or Fsites.

At 200 K, germanium exhibits arather broad center peak for bothlight on and light off, indicative ofpossible multiple-site occupancy.

Regardless of the ambiguity inelucidating specific pion sites fromthe observed channeling profiles, itis clear that for certain temperatureintervals a pion site change occurswhen the carrier concentration is increased (light on). This isqualitatively understood in terms of

FiGURE 3 Pion sues witn respect to lew-index channels in diamond-type structures{HI HA he.-ahedral sites. 7 1 . 72, tetrahedral sites, BC1 SC4, bond-centered sites)

differently structured electronicstates of the pion. From muon-spin-relaxation (|iSR) experiments, wherepositive muons (|i+) are implantedinto semiconductors, it is known rhatmuons form different electronicstates, namely diamagnetic (bare) u.+,"normal" muonium (Mu = u.+ + e~),and "anomalous" muonium.2 Wesuggest that pionium (F/ = 7C++ e~),an analog state to normal muoniumand also to atomic hydrogen with ameson nucleus, is formed because itseems highly unlikely that a barepion would change sites when thecarrier concentration is increased.

169


Hartree-Fock and Hiickel calcula-tions34 demonstrate that the latticepotential for Is hydrogen isotopes atTsites /?* is an absolute minimum.Thus, we conclude that Pi formationoccurs at 7"sites, which is consistentwith either of the aforementioned in-terpretations of pion site location.Furthermore, it is known34 that thelattice potential £«of Is hydrogenisotopes occupying H sites represents an absolute maximum, withE£— £ / > 1.2 eV for atomic hydro-gen in silicon. Formuonium indiamond, Sahoo et al.4 find thatE£- Ef~ 0.8 eV.

We conclude from these calcula-tions that //sites are unstable for Pi.Thus //site occupancy seems plaus-ible only if one assumes that Pi formsbonds with each nearest-neighborgermanium atom. Likewise, if Pi sitsat an AB site, one must conclude thata chemical bond is formed with thenearest-neighbor germanium atomon which the /IBsite exists. Regard-less of which interpretation is viewedas the correct one, Pi states appear toexist that cannot be explained by theformation of normal pionium on Tsites. In analog to u,SR terminology,we associate these sites withanomalous Pi.

References

1. G. Gemmell, Reviews of Modern Physics^, 1 (1974).

2. A. Weidinger et al., Physical Review B 24,6185 (1981); and B. Patterson,Hyperfine Interactions 17'-19, 517 (1984).

3. V. A. Singh et al., Physica StatusSolidiB81,637 (1977).

4. N. Sahoo et a\., Physical Review Letters 50,913 (1983).

170

RESEARCH

Radiation Effects Studies

RADIATION-EFFECTS STUDIES

Operating Experience at the LosAlamos Spallatlon Radiation-EffectsFacility (LASREF) at LAMPFW F Sommer,! K Taylor, and R M

Chavez (Los Alamos) and V'vLohmann (KFA Ji'ilich)

Operation of a new irradiation fa-cility' at the beam stop (Target Sta-tion A 6) at LAMPF began in May1985 The facility is now fully opera-tional. A closed-loop water system, aclosed-loop helium system, remote-handling procedures for activatedmaterials, experimental change-outprocedures, and experimental con-trol equipment are all in place.

Experience dictated a change inirradiation capsules from a systemthat used metal seals to a system thatis completely welded. The seals werefound to be unreliable and difficultto replace by remote means.

Several materials have been ir-radiated in the direct 760-MeV protonbeam. Material property changes, aswell as helium production in a varieryof materials, are being investigated.

A special sample holder that canac:ommodate transmission-electron-microscopy (TEM) specimens,isolate them from the cooling me-dium, maintain a fixed temperature,and retain essentially a stress-freestate has been developed. Remote-hand'.ing retrieval of these specimensis being developed.

Activation-foil measurements arebeing made in order to determine thesecondary-particle flux and spectrum(charged particles and neutrons) thatresult from interaction of the directproton beam with targets at the beamstop. Twelve independent irradiationports, each with an irradiation vol-ume 0.12 by 0.25 by 0.50 m, are avail-able for exposing material to this par-ticle flux (primarily neutrons). Twoirradiations were completed in thisarea during the period from May toDecember 1985. The neutron spec-trum here resembles a fission spec-trum \\ i the addition of neutrons inthe milhon-electron-volt energyrange (high-energy tail). The neu-tron flux, which at a maximum isabout 6 X 1013 n/cm2 s at one of the12 ports, drops down by a factor ofabout 10 at a minimum.

Three independent ports forproton irradiations are in place. Each •has an irradiation volume of about150 cm3. The proton beam has aGaussian intensity profile; the max-imum proton flux at the center of thebeam is 1.2 X 10H />/cm2 s. The beamspot has a size of approximately2c = 5 cm. Four irradiations werecompleted in this area during theperiod from May to December 1985.

RESEARCH

Radiation-Ellects Studies

Four separate irradiations in thedirect proton beam at Los AlamosSpallation Radiation Effects Facility(LASREF) at the LAMPF beam slopwere completed. The irradiationcapsules contained sample materialof aluminum alloys, pure aluminum,Zircalioy, and tungsten—materials \that had been slated as candidates forthe German Spallation NeutronSource (SNQ) target wheel structure,vacuum-to-air window, and targetelement cladding. Extensive in-vestigations aimed at determiningmechanical and physical propertychanges induced by the irradiationwill now be conducted at Julich.

Control equipment, including aclosed-loop helium heat sink, aclosed-loop water heat sink, and attendant instrumentation, was madeoperational. In addition, componentsrequired for a complex in situ testingdevice were irradiated in the neutronenvironment to determine their re-liability. We found that componentssuch as a stepping motor, a load cell,and a linear-variable-differentialtransformer can acceptably toleratethe environment. The in situmeasurements will proceed nextyear.

EXPERIMENT 769 - Beam StopArea

Proton-Irradiation Effects onCandidate Materials for the GermanSpallation Neutron Source (SNQ)

KFA at Julich, Los Alamos

Spokesmen: W, Lohmann and K. Grat (KFA,Mich) and W. Sommer (Los Alamos)

173

RESEARCHRadiation EMects Studies

EXPERIMENT 769 — Beam StopArea

Quantitative Study, by Field-IonMicroscopy, of Radiation Damage inTungsten After Neutron and Protonirradiation

LOS Alamos '•' if; A Mexico Institute oi\i'ni'\.j .-iiiij Tr\ hnoloqv. instituteriiAtomic Energv m China, KFA at Juk'.h

Spokesmen: W. Lohmann (KFA, Jijlich) and W.Sommer (Los Alamos)

Participants: 0. T. Inal and J. Yu

The defects that result from protonand neutron irradiation of tungstenwere studied using the field-ionmicroscope (FIM). The initial stagesof radiation damage can be examinedby noting the configuration, density,and type of defect. This study usedmedium-energy protons as well as aspallation neutron flux for the ir-radiation.-

Annealed tungsten, in an un-irradiated and an irradiated con-dition, was examined in the FIM. Ir-radiations were conducted usingprotons and spallation neutrons atLAMPF. Proton energies were 650and 800 MeV. The neutron spectrumresembled a fission spectrum withthe addition of substantial numbersof neutrons in the 10- to 100-MeVrange. In the proton irradiations,temperature was controlled (by watercooling) to less than 50 ° C; the tem-perature for the neutron irradiationswas measured at 125° C.

The calculated diffusion coeffi-cients of vacancies at 323 and 398 Kin tungsten are 1O~54 and 1O~44 cm2/s,respectively, which means that thevacancies are essentially immobile.The interstitials at this temperatureare mobile and should diffuse to asink, leaving few interstitials in thematrix; this was confirmed by the FIM

in this study. The concentration ofvacancies that survived recombina-tion and were observed with the FIMwas 1 to 3% of the calculated dis-placements per atom (dpa). Wesuspect that the remainder haveundergone vacancy-interstitial re-combination or have found a sink.The vacancy concentrations resultingfrom fluences of 10" and 1O24 p/m2

were 2.5 X 10~3and 1.0-1.6X 1()~2,respectively. The neutron-irradiatedsamples contained a vacancy concen-tration of 4 X 10~3 after a fluence of1023 n/m2. Depleted zones contain-ing a thousand or more vacant latticesites along with smaller zones con-taining from 30 to 300 vacant latticesites were observed in the irradiatedsamples. The shape of the smallerzones was uniform and rounded; thelarger depleted volumes split intonodes.

Un-irradiated samples of the samestock were examined for defects. Thecalculated equilibrium vacancy con-centration at 300 K is 10~56; therefore,vacancies should not be found. Thisproved correct for the samples ex-amined, as no vacancies or void vol-umes were found.

The data indicated that the numberof vacancies increases with increas-ing fluence and that the numbersurviving recombination is from 1 to3% of the calculated dpa. The mostnumerous defect for both the protonand neutron irradiations was thesingle vacancy. Depleted zcnes wereof two basic sizes: (1) 30 to 300 va-cant lattice sites or (2) over 1000 va-cant lattice sites.

174

RESEARCHRadiation-Effects Studies

A new irradiation facility, LASREF(Los Alamos Spallation Radiation-Ef-fects Facility), has been completed atthe beam stop area at LAMPF. Irradia-tions are possible in the primaryproton beam and in the secondary'neutron flux resulting from interac-tions of the primary beam with theisotope production targets and withthe copper beam stop. High-purityactivation foils are being irradiated,the gamma spectrum is beinganalyzed to determine the activity ofthe spallation products, and themeasured activity is being used asinput in a computer code to unfoldthe proton and neutron energy spec-trum at LASREF. This analysis willalso aid in developing a simplifieddosimetry package that will be ir-radiated with each experiment,

Measurements are being made atlocations where proton irradiationsare possible in order to determinethe energy spectrum and flux of thesecondary neutrons that would im-pinge on peripheral experimentalequipment. Aluminum samples areplaced directly in the proton beam toanalyze the beam spot size, beamdegradation, and the proton flux.

A pneumatic rabbit system hasbeen built to measure the flux ofsecondary neutrons and protons inthe neutron-irradiation ports. Fourrabbit tubes allow measurements inradial locations 0.12,0.18,0.27, and

0.38 m off the beam center line. Diskshaped foils of titanium, nickel, zinc,iron, copper, vanadium, scandium,gold, cobalt, and aluminum, eachwith a center hole, are strung on analuminum center wire inside analuminum capsule to assure identification. Capsules are pneumaticallyplaced in the neutron-irradiation portusing helium gas as a propellant, andthe foils are irradiated for 3 to 24 h.Because of the high activation ofshort-lived isotopes, the capsules andfoils are allowed to decay for 48 hbefore analysis begins. Results of theirradiations give the effect of isotopeproduction target loading on thesecondary neutron energy spectrumin the neutron-irradiation ports.

Five irradiations have been madeat the neutron-irradiation portoutside the isotope productiontargets. After the irradiations werecompleted, the insert was moved to aneutron-irradiation port outside thecopper beam stop, where sevenmeasurements were made.

EXPERIMENT 936 — RadiationDamage

Additional Measurements of theRadiation Environment at the LosAlamos Spallation Radiation-EffectsFacility (LASREF) at LAMPF

Los Alamos, Iowa State Univ

Spokesmen: D. R. Davidson and W. F. Sommer(Los Alamos)

Participants: ft C. Reedy and M. S. Wechsler

175

RESEftRCHRadiation-Ettects Studies

EXPERIMENT 943 — RadiationDamage

Microstructural Evolution UnderParticle Irradiation

'SMutf 01 «ioi'nic Eneigv in L.rnnj LO

Spokesmen: J. Yu (Institute of Atomic Energy,China) and W F Sommer (Los Alamos)

Participant: J. N. Bradbury

Structural materials for advancedenergy sources, such as magneticallyand menially confined thermonuclear reactors, are subjected to (1) aradiation environment thai produceshigh energy displacement cascadesand (2) transmutation products thatinclude helium. A similar environmerit exists at the Los Alamos Spolia-tion Radiaiion-lilfects Facility(LASREF), where a spallation neu-tron flux is available as well as thedirect proton beam. The major dif-ferences among the three environ-ments—fusion, LAMPF spaliationneutrons, and 800-MeV protons— arethe details of point-defect productionrates, transmutation-product produc-tion rates, and the recoil energy ofdisplaced atoms.

In preparation for an experimentthat addresses the relative effects ofthe above parameters by exposingcontrol materials to both the spalla-tion neutron flux and the directproton beam, we have formulated atheory that predicts the microstruc-tural evolution that s h e ' d proceedunder the two different conditions.The ratio of the helium productionrate to the atomic-displacement rateis predicted to be 10 times greater inthe direct proton beam than in theneutron flux. If the prediction andexperiment can be brought into

agreement, it maybe possihle to ex-trapolate data for microstructuralevolution and the attendant mechani-cal property changes to the fusioncase, in which the ratio is similar tothat for the spallation neutron casebut the recoil atom energy spectrumis different.

For the theory, we consider thatimmediately after a high energycascade event a vacancy-rich regionexists near the primary event site, andthat an interstitial-rich /one, formedby collision chains, exists some dis-tance from the primary event site.Transmutation-product helium candiffuse into the vacancy-rich zoneand stabilize bubble nuclei, whichwill later grow if sufficient vacanciesand helium atoms diffuse to thenucleus. These bubbles are the sinksfor excess radiation-produced vacan-cies. The excess radiation-producedinterstitials migrate and bond. If thebinding energy is high enough, a di-interstitial is considered to be astable dislocation loop nucleus. Theloop nuclei grow if they receive moreinterstitials than vacancies; this rep-resents material swelling because thebubbles do not cause a lattice con-traction to offset the dilation causedby the growing dislocation loops.

We consider further that the inter-stitial loop growth process can berepresented by a Langevin equation.If the growth process at time / isassumed to be dependent only on theinstantaneous interstitial concentra-tion and the instantaneous

176

RESEARCHRadiation-Ellects Studies

microstructural state (dislocations,bubbles, and grain boundaries) andindependent or previous history, thegrowth process can be considered inbe a Markov process. Application otan equivalent Fokker Plank equationallows deduction ot an interstitial-loop illicit .rioii and growth equa-tion, the solution of which yields aninterstitial loop distribution func-tion.

Use of appropriate materialparameters gives the incubation andgrowth regimes of swelling and alsoallows a determination of the max-imum swelling temperature. Theseresults predict a maximum swellingtemperature of 117"C for aluminum,550 "C for stainless steel, and 11()(>°Cfor molyhdenum, in good agreementwith experimental results.

Basically, the maximum swellingtemperature is a function of only .*,.,e{,/6™ (p,v + p8), and Np. The maximum swelling temperature in-creases as (p/v+ pe), Np, and z1

m/"m

increase, and decreases as s,. in-creases. Here, s,, is the vacancy-forma-tion entropy, e{, is the vacancy-forma-tion energy, e™ is the vacancymobility energy, pN is the networkdislocation density, p8 is the disloca-tion loop density, and Nf, is the production rate of vacancies and interstitials per unit volume under irradia-tion.

Further, the resolution charac-teristics for interstitial dislocationloops have a strong bearing on their

evolution because the threshold forthe resolution of an interstitial loop islower than tiiat for the helium in thebubbles. As vacancies also condenseat interstitial loops, the resolution isenhanced.

The above treatment also gives aset of equations lor the evolution ofbubbles and an approximate solutionof a distribution function for bubblesize as a function of fluence and tem-perature. The distribution functiongives the number of bubbles of si/e rat time /, N( r,t)dr, as a function ofsize r.

We found that M r, t) dr increaseswith fluence. Also, the peak value ofN( r,t)dt shifts to higher r with in-creasing fluence. Nucleation de-pends mainly on helium concentra-tion and defect cluster concentration,whereas bubble growth is controlledmainly by the vacancy concentrationand a fluctuation coefficient.

If suitable parameters are chosen, areasonable distribution function forbubble size can be obtained. Thehelium diffusion coefficient is lessthan that for vacancies by five ordersof magnitude. The fraction of heliumremaining in matrix is less than 1()~2;the majority of the helium is associated with the bubbles.

RESEARCH


BIOMEDICAL RESEARCH AND INSTRUMENTATION

Radiobiology of UltrasoR X RaysM R Raiu.S G Carpenter, J J

Chmielewski M E Schillaci. P LGchor andM E Wilder (Los Alamos)

The objective of this program is toprovide evidence to further constrainand test assumptions used in modelsfor the biological effect of radiation.Ultrasoft x rays (with energies lessthan a few kiloelectron volts) are ofinterest in radiobiology because theydeposit energy over spatialdimensions comparable with those ofcritical structures within the cell,such as DNA strands and metaphasechromosomes.

During the past year, we com-pleted the initial phase of our in-vestigations using V-79 hamster cells.Our first experiments confirmed theearlier Harwell results1 for cell kill-ing. We found relative-biological-ef-fectiveness (RBE) values for C-K,,(0.28-keV),Al-Ka(1.5-keV),andCu-Ka (8.0-keV) x rays, referenced to250-keV-peakxrays of 3.0,1.7, and

1.3, respectively, at 20%survival. Inaddition, we performed new studiesof the increased sensitivity of cells toradiation in the presence of oxygen.We found oxygen-enhancement-ratio(OER) values for carbon, aluminum,and copper x rays of 1.8,2.1, and 2.5,respectively, at 20% survival. Also, wemeasured variations in cell killingwith cell volume, which correlateswith age in the cell cycle. The cell-cycle responses after exposure tocarbon and aluminum x rays werevery similar to those for 250-keV-peakx rays.

Computer simulations2 show thatnearly one-third of the energy of 250-keV-peak x rays is deposited by ter-minal low-energy secondary elec-trons having a concentrated, short-track structure characteristic of ultra-soft x rays. Our results show that theeffectiveness of hard x rays is primar-ily due to ihese terminal electrontracks; however, oxygen has a greaterinfluence on the more widely spacedlesions associated with the majorshare of the energy deposition forhard x rays, but produced to a lesserextent with ultrasoft x rays.

References

1. R. Cox.J. Thacker, and D. T. Goodhead, International Journal of Radia-tion Biology 31,561 (1977); and D. T. Goodhead, J. Thacker, and R. Cox,International Journal of Radiation Biology 36,101 f 1978).

2. D.J. Brenner and M. Zaider, Radiation Research*)*), 492 (1984).

178

RESEARCH


A completely implantable (passive) hyperthermia applicator is beingdeveloped. Tests in gel phantoms in-dicate that heat can be localized indepth without a significant temperature increase near the implantedsubdermal-receiving antenna. It hasalso been demonstrated that the average temperature increase in the treatment region can be regulated by control of the voltage-current phase atthe transmitting antenna. We haveformed a collaboration v/ith theWashington University (MallinckrodtInstitute of Radiology) for animaltests and, eventually, trials on deep-seated malignant tumors in humans.The DOE has filed a patent applica-tion on this instrument.

Javier Magrina at the TrumanMedical Center in Kansas City reportsthat all of the six initial patients withcervical intraepithelhl neoplasia(CIN) have responded with re-mission of their disease following hyperthermia treatment using the LosAlamos apparatus. He has found vir-tually no complications with thistechnique, including those com-monly experienced with surgical,cryosurgical, or laser therapy.

The software for calculating tran-sient Uk-.iperature distribution in tis-sue has been expanded to in-corporate user-defined models forsimulation of the hyperthermia gen-erator specifications, includingpower output, temperature monitorlocation, and temperature-feedbackloop characteristics.

A hyperthermia probe capable ofheating larger tissue volumes hasbeen supplied to our collaborators atthe Renji Hospital in Shanghai,where treatments of brain cancercontinue, and an electrosurgical de-vice has been developed that com-bines cutting and coagulating capa-bility in one instrument. A patent ap-plication has been filed.

Another patent application hasbeen filed on a dissolvable stent,which is intended for use in bloodvessel surgery.

InstrumentationJ. D. Doss and C W. McCabe (Los

Alamos)

179

RESEARCHNuclear Chemistiv

NUCLEAR CHEMISTRY


Plon Single Charge Exchange In 7Lito the ISGharlc-Analog Ground Stateof'Be

- - •'•larni.is. nstiiuteol Aiomn. l i ie iyv ..-itr- .'i|in..i. i.. hi iu

Spokesman: B. J. Dropesky (Los Alamos)

Participants B. J Dropesky, G. C. Giesler, M J.Leitch, L C Liu, C J Orth, Ft. J Estep. L £.Ussery, and A Cui

In this study we are particularlyinterested in the interference between .v and p-wave JIN amplitudes asmanifested in the cross section forthe pion single charge-exchange(SCX) reaction. Hvidence for this interference was first observed by thedramatic and unexpected drop in theforward-angle cross sections for thel4N(n+,7t")15O isobaric-analog state(IAS) reactions measured at 48 MeVwith the LAMPF TI"spectrometer.'The theoretical model of Kaufmannand Gibbs,2 which includes the .*• andp-wave JtN-amplitude cancellation,predicts a deep minimum in the for-ward-angle cross section at about50 MeV for such an SCX reaction.This was confirmed for thereaction HC(Ji+,n")HN (IAS)bymeasurements3 with the K° spec-trometer that extended the 0 ° excita-tion function for this reaction downto near 30 MeV.

Our activation measurements' inExp. 553 of the angle integratedcross section as a function of energyfor the SCX reaction '3C(n+,7i")1;)N(10 min, IAS) showed a dip in theexcitation function at about 70 MeV.This dip is another manifestation ofth~ interference between \ andp waves. The Kaufmann-Gibos calcu-lation for this angle-integrated crosssection predicted a minimum in theexcitation function near6() ratherthan 70 MeV.

In this experiment we have in-vestigated another example of anSCX reaction that leads to anisobaric-analog ground state, namely7Li(n+,7t0)7Be (53 days, IAS). Thisstudy is complicated by the fact thatone other bound state, the first ex-cited state in 7Be y 429 keV resultingfrom a nonanalogspin-flip transition,is also involved. However, very recently at TRIUMFwe measured thecross section to this nonanalog stateusing the prompt y technique overthe energy range from 50 to 90 MeV,and at LAMPFwe measured the yieldof 53-day 7Be over the energy rangefrom 35 to 90 MeV. These measurements give us the sum of the crosssections to both the analog andnonanalog states. By subtraction weobtain the excitation function for theIAS tnnsition alone and look foradip caused by s- and p-wave inter-ference. Of particular interest iswhether this dip, if observed, isshifted upward in energy when rom-pared with theory, as we saw fo. I3C.Because the spin flip transitionshould not have any sharp structure

180

RESEARCH

' I '1 ' . try

in it:; energy dependence, such a dipshould also appear in the cross sectton for the sum of the two transitiou.v

The cross sections tor these reartions in Li were measured severalyears ago by shamai ft al.sat LAMPFC7!) to 2SU MeV) ;md by Altman et al."at SIN i 90 to 21(i MeV). They notedthat the cross section to thenonanalog state is about one thirdthat ot the analog transition. AtLAMPF. the it" spectrometermeasurements of the 0 cross section for the Li(n+,it")"Be (IAS) reaction have been made from about 3" to100 MeV, and a distinct minimum at==42 MeV was observed. The Kaufmann Gihbs calculation puts the interference minimum at -~50 MeV, acanonical energy that appears to beindependent of the nuclear size intheir model.

To determine the excitation func-tion for the "Li(;if~.;t"f Be ( S3-day,IAS ) reaction over the energy rangefrom 3S to 90 MeV, we irradiateddisks of natural lithium metal, sealedin thin windowed containers, in the7t+ beam of the LEP channel for anappropriate number of hours. Theelectron-free pion flux emergingfrom the "S ft particle beamseparator." which was coupled to theLEP channel, ranged from-i X lohto1 X in" r+/s. After irradiation, thelithium disks were transferred, in aninert atmosphere, to new containers,and the induced 53-day Be y ray(-i~K keV) activity was measured withour low background, high resolutiongermanium or Ge( Li) y spectrometers in the Nuclear ChemistryLaboratory at LAMPF.

The absolute cross section for thesum ot the contributions of the\i(it+,n") reactions to the first excited and ground states of Be willcome from relating the yield of Be tothe activity of IS hj'N'a induced inthin aluminum flux monitor foilscoupled with the lithium targets andthe cross sections for therAl(7t+,.v,V )-'Na reaction we de-termined previously," down toSO MeV. For this experiment, therefore, it was necessary for us to make afew -iO-min irradiations, at 3S and45 MeV, of packets of aluminum foilplus Pilot B scintillator disks to de-termine the 2"Al(7t+,.YM2'lNa cross sections relative ;o our well-established12C(it+,;tAr)"c (2O.H-min) primarycross sections at these energies.''

For the lithium targets, which are~ 100 mg/cm",:secondary (p,n) reac-tions from protons generated by pioninteractions in the target can contribute to the yield of 53-day "Be. Because of target fabrication and oxida-tion problems, it was not feasible toconsider an experimental study ofthese secondary effects as a functionof target thickness. Therefore, we intend to calculate the magnitude ofthese corrections by means of theformalism developed in our group byJ. J. H. Berlijn and the computer program written by W. R. Gibbs of GroupT-S.

181

RESEARCH

Our preliminary cross sections forthe reaction "Li (Jt+,7t")"'Be to the sumof the analog plus nonanalog statesover the energy range from 3^ to90 MeV are shown in Fig. 1. No correciions have yet been made forsecondary ip,n) contributions to themeasured cross sections. Also, subtraction of the contribution to the S.Vday Be by transitions to thenonanalog i29 keV excited stale willhave to wait until the recent TRIUMl'data can be processed. However, wecan point out that the present datashow that our measured cross sectionfor the sum of the analog andnonanalog transitions at 90 MeV is inagreement with the earlier measurement of Altman et al.6 On the otherhand, our 70-MeV cross section(1.16 ± 0.19 mb) is in disagreementwith the earlier value of Shamai et al.'( = 2 .7±1 mb).

Our preliminary excitation func-tion shows a monoionic decrease incross section as the energy is loweredfrom 90 to ~ So MeV, and then anincrease in going to 3S MeV. Thiswould appear to reflect the interferenee between .<• and /> wave KNamplitudes t1 at accounted lor theminimum (at H2 MeV) observed intheO° excitation function for thisreaction measured with the TC"spectrometer/" Despite the missingvalue at 50 MeV, the minimum in ourexcitation function is quite broad, aswas noted for the 0° measurements,particularly when compared with theminimum observed for the SCX reac-tions in KCand 15N, for example.7

Likewise, this minimum is muchbroader than the one we observed inthe excitation function of the angle-integrated cross sections for the13C(71+,JI°)13N (IAS) reaction.4

o-(m

b)

2.0

1.5

1.0

0.5

0

- .

-

30

'llt

40

lii i

50 60

TV

T 1

-

-

1 J

> i

70 80 90(MeV)

FIGURE 1 Energy dependence ol the angle-integrated cross section lor the sum ol•h? transitions to the analog and nonanalog states (or the single-charge-exchangereaction 7Li(7r+,7t°)7Be

182

RESEARCHi ' i i i • [ • i , l r /

References

1. M. 1). Cooper, H. W Baer, R. Bolton, I 1). Bowman, 1'. Cverna, N. S. p King,et al., Physical Review Letters 52, 1 11)0 ( I98i ).

2. W BKaufmannandVC. R.Gihbs. Physical Review C 28, 12H6 ( 19H.-W.

3. J. L. I'llman, P.W. Y. AlonsJ. K. Kraushaar.J. M.Mitchell, R.J. Peterson, R.A. Ristinen, et al., "Pion Single Charge Exchange on MC from 35 to295 MeV" ( submitted lo Physical Rerieir ('. ).

4. L. H. I'sst-n,', D.J. VieiraJ.J . Berlijn. d. VC1. Butler, B.J. Dropesky, G. C.Giesler, N. Imanishi, M.J. Leitch, and R. S. Rundberg, "Excitation Functionfor the Pion Single Charge Exchange Reaction llC(;t+,jt")HN (g.s.)" d o besubmitted to Physical Review C ).

5. Y. Shamai.J. Alster, D. Ashery, S. Cochavi, M. A. Moinester, and A. 1. Yavin,Physical Review Letters 36,82 ( 19^6).

6. A. Altman,J. Alster, D. Asher\-, 1. Navon, H. J. Pleiffer, H. K. Walter, et al.,Physical Review Letters 39, Hfo ( 19"7?).

7. F. Irom, H. W. Baer, J. D. Bowman, M. D. Cooper. E. Piasetzky, U.Sennhauser, et al.. Physical Review C31, 1464 (1985); and F. Irom, M.J.Leitch, H. W. Baer.J. D. Bowman, M. D. Cooper, B.J. Dropesky, E.Piasetzky, andj. N. Knudson, Physical Review Letters 55, 1862 (1985).

8. B.J. Dropesky, G. W. Butler, G. C. Giesler, C.J. Orth, and R. A. Williams,Physical Review C 32,1305 (1985).

9. G. W. Butler, B.J. Dropesky, C.J. Orth, R. E. L. Green, R. G. Korteling, andG. K. Y. Lam, Physical Review C26, 1737 (1982).

183

RESEARCH

. f -V

Tlme-of-Fllght Isochronous (IOFI)Spectrometer

J V Wouters, K Vann. D J Vieua, F K WohnR -I Kraus H Wollnik. G VV duller J RSims. J W •Jan Dyke. S Archuletta, M. Mays,j R Zer^ekh, D D Kercher

Introduction

This rept>n is the third in ,t scries i>lprogress rcpi >ns describing the tlfsign, cnnsiriktiun, .incl tt'.slin^ of ilu-lime til Iliglit isoehronous (TOl-'l )spectrometer and its associatedseenndan.'heatn line TOI'I, \\ hich isbeing constructed jointly by INC andMl' Divisions, is designed to measurein a systematic tashion the groundstale masses ol the light neutron richnuclei with .-1 < "() that \\J lar fromthe valley of P stability. Three majorgoals were achieved during the pastyear:

1. the second half of the transportline was installed and the entireline was tested;

2. the four dipole magnets thatconstitute the spectrometerwere field mapped and optimized; and

TARGETCHAMBER^

MAINLAMPF

^ P R O T O N BEAMBEAM

~~~ Tl TRANSPORTt~~>^-Li LINE

3 the spectromete;- was installedand tested, and an initial set oldata was acquired.

Here we describe these major accomplishments. For a summary ol thescientific goals and overall design olthe TOFI spectrometer, see the twoprevious LAMPI' Progress Keports.''

Secondary B^arn Transport Line

The secondary beam line for theTOI'I spectrometer was completed inMarch of 1985 with the installation ofthe second half of the line. This transport line consists of four quadrupole-triplet focusing magnets, a mass-to-charge filler, and several x, y steeringmagnets (see Fig. 1). The purpose ofthe transport line is threefold:

1. to provide a focused image ofthe target at the entrance toTOFI while capturing the largest solid angle possible fromthe production target;

2. to reduce the transmission ofhigh-yield light ions (that is,protons, deutcions, alphas, andneutral particles) that wouldnormally saturate the first tim-ing detector; and

3. to physically remove the spec-trometer from the LAMPF high-intensity beam line in such away that easy access to the sys-tem is obtained.

To achieve these goals the trans-port line optics is arranged as twoalmost identical quasi telescopic sec-tions using four quadrupole triplers.The first section incorporates an elec-irostatic deflector and dipole magnetlocated immediately in front of thesecond quadrupole triplet to act as a

•incl

1K-I

RESEARCH

c r u d e m.i-*-. '•' c h a r g e l i l t e r t oe l i m i n a t e inn1 .1 , o t t h e h i g h \ i f k l l i g h ti o n s . A i . . l l i i n a i n r 1- p i . t e - . ' d u a n i nI e i i l l e d i a l e tt n al pos>in MI b e t w e e n

t h e t w o t e l e s o i p : r s ec t it His It • d e l m e

t h e t n a s s I,, c h a r g e t r a n s m i s s i o n v \

era i t e s t s w e r e t . i r n c d mi l in

c h a r a c t e r i z e a n d o p t u - . u ' e t h e t r a n s

p o r t l i n e p e r l o i m a n e e w u h re s p e d It >

s o l i d . i n g l e . u u l mi n i i e n i u i n a n d

ina.vs ti < i h a r g e t r a n s n n s s i . in

p n > p e n i r s . .is w e l l .is i n era!I uu i g e

quaiin

The ii\ii)s|>t in Imc was tuned usingvarious alpha souri es and light react ion products originating I in in Hi inMeV proton bombardments of a natural thorium target Kach quadrupoletriplet was characterized separatelyin point to point focusing tests usinga particles. These imaging studiesused a position sensitive mulhwireproportional counter" located at theintermediate and final focusing posi-tions. Further focusing studies usingsome or all ot the triplets were carried out with a sources located in thescattering chamber or at positionsalong the transport line. Figure 2shows the type of images obtained atthe final focusing position ( 1) forasource located at the target positionand i 2) for a projected image of acollimator located in the transportline to cm from the target.

To deliver a large solid angle to thespectrometer, the transport line reduces the angular spread of the reac-tion products. This presents anenlarged image ot the target regionto the spectrometer. Using the general ion optical systems code(GlGS), the vand)'magnificationswere calculated1 to be 2.0 and 2.3,respectively, which agrees with our

measurements exactly. I sing various sized o illiniators to define thesolid angle acceptance oi the line,w e s t u d i e d i r a i i M i i i s s i n i i v e r s u s s i i l u l

.ingle ()nly a S",, intensity l< >s.s In mitlie target to the fin.'I locus wasmeasured lor tile design siilid angleacceptance of _!.-> msr

I sing a nniliienergy, mixed itsource ol "V,dand.-'-"Thanda largearea! in1, in mnr ) silicon detector, themomentum transmission ol the linew.is determined in ilie same !as.!iionas that reported pre\ iousiy lor thefirst hall of the line." This momenturn transmission curve is basicallyGaussian in shape, with a width of5p/p = 2H"b ( FW'H.M ). This is morethan sufficient to fill the spectrometer, which has a design acceptance of 8p//) = -i%. Additional testsshowed that the optimized tune cieveloped for one particular a energygives good solutions at otherenergies if scaled according tomomentum.

Finally, to investigate the filteringproperties of the mass-to-charge( m/q) filter, a Afc-E silicon telescopewas used to identify proton, deu-teron, triton, 'He, and a reactionproducts. For these tests the transportline was set fora particular morncn-tum-tocharge value ( 190 MeV/c/r/)and then the electric fielci of the( m/q ) filter was tuned to variousvalues in order to select different( m/q ) ratios. By comparing the intensity ol identified alphas andtritons at different ( m/q ) settings,the ( m/q ) transmission ol the trans

50 -

FiCjiJRE. 2 image'-, ob:.er -eel lend ol the transport 'me tor a -''a source lOCateU 3t the pr:ylu:'Dosidon and (b) at thi-- irUHficing poiition appi(."' • in latel, I ialithiongh the uansooM imeior ,iCOHirnatoi located 4O cm iliv/vi'he a w j i c f i I a "get I', ."-.-it1:" i 'CC'ilar •maqn •'•;''ilTtH'fK" I !ha'

al at theAmtinn tattjet

tMic locusA , i ,

lout)le oiilv-ln^arn olM.I) ..I

f'llf'. ! ; Ih

RESEARCH

port line was determined A dearfiltering of the neighboring i in q \species was observed. The .-! (J transmission cuive is semi Gaussian witha w i cl t h o f 15.-1, Q> / (A/Q) = IV \,(l-'W'HM ) and a tail extending to thehigh A/Q side of the peak. Morespecifically, at a setting optimized fortritons (that is. A, Q= 3), the intensity ol a particles (A/Q= 1) wasreduced by more than three orders olmagnitude. This filtering isparticularly important in our futureexperiments because the yields ofthe exotic nuclei of interest will beseveral orders of magnitude lowerthan those of p, d, a, and other recoils with. 4/Q S 2.

In conclusion, all these measuremerits agreed with the expected design performance of the transportline.

Magnet Mapping andOptimization

Mapping of the spectrometerdipole magnets was divided intothree separate tasks:

1. optimizingthesizeoftheRo.seshims used to extend the radialwidth of the uniform field region,

2. determining the shape and sizeof iron wedges used to tilt andstraighten the effective fieldboundaries (EFBs) at the en-trance and exit of each magnet,and

y mapping the uniform portion ofdie magnetic fi /Id in order tobuik. surface inhomogeneitycoil;-:.

These measurements and trimmingprocedures were developed usingthe first magnet. The optimized design lor the Rose shims and wedgesdetermined for the first dipole we.'eduplicated, installed, and checkedon (he remaining three magnets. Because the four dipoles were nearlyidentical, no reoptimization of theseshims was required. However, thesurface coils were custom designedfor each magnet in order to removefield non-uniformities that wereunique to each dipole magnet. Afterspending nearly 5 months measuringand optimizing the first dipole, wecompleted work on the remainingthree dipoles in only 2 months.

Optimization of the Rose shimswas done using a simple iterativetechnique in which several radialscans across the pole face were ob-tained using a Hall probe attached toan x,y plotter. From these scans theshape of the field could be de-termined to a relative accuracy of0.2 Gout of an overall field of 5.7 kG.Absolute calibration of the probe wasunnecessary and drift correctionscould be ignored because of theshort (30-s) scan period. The widthof the Rose shims (curved segmentsof 2.S-mm-thick magnet steel at-tached to the inner and outer radii ofthe top and bottom poles) waschanged after each scan until thewidest uniform field region was ohtained. The final field shape introduced a slight (0.5-G) field hump

186

RESEARCHar Chemistrv

at both ihe inner and miter radii tocompensate tor the natural decreasein the magnetic field as the distancefrom the central radius increases. Acomplication to the trimming ot theRose shims arose in the region ot thetop pule piece supports. A noticeablenarrowing of the uniform field regionwas observed at these locations. Thiseffect was corrected by mountingsmall iron rings around ihe supports,VC'iih these optimization proceduresthe radial width ot the uniform fieldregion (defined here as ±0.5 G ) wasincreased from 15 to 20 cm fora polewidth of M) cm and a magnetic gap of9.6 cm.

Trimming the entrance and exiteffective field boundaries ot themagnet was done using an iterativetechnique that determined theseboundaries at equal spacings acrossthe width of the pole. Ten Hall-probescans taken parallel to the particletrajectory at the entrance and exit ofeach magnet and going from thefield-free region outside the magnetto the uniform-field ;egion were ob-tained. Using an interactive analysiscode, we transformed these individ-ual scans from the measurementcoordinates to magnet coordinates,which we then used to calculate thelocation of the EFB along each scanto an accuracy of 0.25 mm.

Steel shims placed on the slopedportions of the entrance/exit poleswere designed so that all scans resuited in the same EFB location. Fourtypes of shims were finally constructed for each magnet. The outerradius shims were simple 2.5mmthick, 2.5- and 5.0 cm long metal

strips that were bolted in place. Theinner radius shims were fairly com-plicated wedges that had to be oplimized using many iterations. Thesewedges countered the tendency olthe field to fall off too quickly nearthe corners of the poles and thusproduce a curved EFB. Two types ofwedges and two types of straightshims were required because of thedifference between the end ot themagnet that had the current leadsand the end that did not. The finaleffective field boundaries were flat(to 0.^6 mm over half the central arc-length of ""8 cm ) across the usableportion of the magnet pole width(20cm).

The final step in the uipole op-timization was to produce completefield maps taken near the top andbottom pole pieces in order to con-struct top and bottom surface coils toreduce the remaining field in-homogeneities unique to eachmagnet. This step was especially dif-ficult because of the dual require-ments for obtaining 0.1 -G accuracy inthe homogeneous portion of the fieldand for extending the map into thefringing field regions of the magnetwith lower resolution. A new field-mapping technique that acquires twofield maps simultaneously was de-veloped to accomplish this dual goal.

The first map used a nuclear mag-netic resonance (NMR) magneto-meter to measure the field, and thesecond map used a temperature-stabilized Hall probe. The NMR field

187

RESEARCH

map was accurate in considerablybetter than 0.05 G, but could not ob-tain data in the fringe fields ol themagnets. The Hall map covered theentire region that needed to bemapped, hut was accurate to only 5 Gabsolute.

A composite field map wasproduced by using the NMR mapwhere the magnetometer was stableand by filling the remaining regionswith a corrected 1 kill map. This correction consisted of finding the twomost recent data points where boththe NMR and Hall maps were validand then normalizing the Hall data tothe NMR data. In this fashion theHall-probe data were continuouslyrecalibrated on an absolute scale,yielding fringing field data with anaccuracy of o.S G.

The resulting field maps for thetop and bottom poles were modifiedin several ways in order to create thefinal contour maps needed to designthe surface inhomogeneity coils.

First, the maps had to be extended,using a linear-extrapolation routine,to regions that could not he reachedby the field-mapping probes becauseof obstructions.

Second, a boundary' region was de-fined around the map that was 3.2 cmwide and located 3.2 cm away fromthe effective surface coil outer edge.Outside this boundary' region themap was set to a constant value; inside, the map was set to the final field

value. The values of the data pointswithin the boundary legion itselfwere determined by doing a linearinterpolation across the boundary', Inthis fashion the contour lines of thefield map could be smoothly closed.

Third, the maps were smoothedseveral times using a technique thatlooked at adjacent data points andaveraged over them to redetenuinethe central data point.

Finally, the maps were drawn fullsize. The contours were cut by handin one place and reconnected to forma spiral, permitting current to be fedin at one point of the circuit boardand returned at another. The finalcontour spacing was 0.75 G, produc-ing a field of approximately that uni-formity. The field-uniformity im-provement resulting from these sur-face coils can be seen in Fig. 3(a),which shows an uncorrected fieldmap, and Fig. 3( b), which shows thesame field map after the surface coilhas been energized. The fieldhomogeneity has been improved byapproximately a factor of 3.

Spectrometer Installation andTuneup

After the magnetic-field optimiza-tion of each dipole was completed,the magnets underwent final as-sembly. This involved the installationof the inhomogeneity surface coils,the quadrupole/hexapole surfacecoils, and the vacuum tank. (Thequadrupole/hexapole surface coilswere included to adjust the first- and

1HH

RESEARCH

sec i uid field indices to opiimi/.e I lieisochronous and focusing propertiesof ihe spectrometer> "1 he dipoleswere assembled and moved into theTOl-'l experimental area where theywere aligned Lincl connected to thecoo 11 ug w Liter supply ;ind the specin Miieter pi >wer supply. Bv the end otOctober ll>.-iS, the instnll;iiion of thevacuum svsicm was coin pie ted andthe spectrometer was under vacuum

\lter lhe momentum c> ilhmator;ind hist timing detectors were installed, the spectrometer was a imedon lor ilie first time on November 1 1.19K5. Within the first day the spectrometer h;id achieved its mass resolving power design goal ofM,-AM= iuiHi, with the measurementot "'"Am u particles show ing LI tir . ingaccuracy of it MI ps out of a total transit time of mm us. After 2 weeks oflurther off line and on line testing,data collection tor the lirst experimem was begun. Data collectioncontinued until mid December,when the LAMPl' production runended.

The purpose of this initial tlineupexperiment \v:is to provide a prelimi-nary data set to develop the data-analysis procedures and to deline anyremaining improvements neededbefore the next beam period starts inthe summer of 1986. At lhal time thetirst experiment will be completed.The experiment seeks to measure themasses of neutron rich nuclei in theZ= 10 to 12 region in an attempt tofurther understand the appearance ofLI rapid nuclear shape transition occurrmg in these nuclei.

References

I Progress at LAMI'F," Los Alamos National Laboratory report LA-1(K)7()PR( April 19H-i), pp. 121 12 i.

2. Progress ;it LAMPF," Los Alamos National Laboratory report LA-10429-PR(April l9H=>),pp. 189 192 and 192-195.

3. J. M. Wouters, D.J. Vieira, H. Wollnik. H. Hnge, S. Kowalski, and K. L.Brown, Suebjar Instruments & Methods A240, "'"'•90 ( 1985), and referen-ces therein.

189

RESEARCH

Pan ..isotope Production

RADIOISOTOPE PRODUCTION

isotope Production and Separation

Radioisotope Production

K E Peterson -> iJ r iH inSegura. F H Seurer 0.J Stemkruger U -'• OttBarnes and P P.. I \\ anp(Group INC 3, LOb AictrrK

L.iyior

The medical radioisotopes research program in INC 11 (formerlyINC-3) continues to supply radioisotopes to the medical researchcommunity. Several of these radioisotopes are uniquely produced hereand many others can only beproduced in quantity at LAMFF. Twonew isotopes were made availablethis vear: 32Si for inhalation studies

and "Ti to be used in the 44Ti/4\Scgenerator. The "Sc is a positron-emit-ting isotope that concentrates in thebone. Both of these new radioisotopes were obtained from initialresearch targets. Additional informa-tion will be presented as proceduresare finalized.

In 102 shipments, -iS.6 Ci of 13radioisotopes were distributed dur-ing FY 1985. These data are sum-marized in Table 1.

190

RESEARCH

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191

RESEARCH

Electrolytic Separation ofSelenium Isotopes fromProton-Irradiated Targets

Arsenic "'I has many applicationsin medicine and environmental toxi-cology. It is a positron I'tnitter. "V.i!:int; it a potentially valuable isotopein positron emission tomography( PFT); it might be conjugated to ap-propriate monoclonal antibodies loruse in cancer therapy; and it can beused as a tracer in biochemicalstudies to evaluate the environmentalimpact of arsenic produced in coalcombustion and geothermal emis-sions. For many applications it is important to have the radioarsenic invery high specific activity.

Probably the best approach tor theproduction of ""2As is by use of a"Sc/"As radiochetnical generatorsystem. Selenium-"7! can beproduced in reasonable yield by irradiating RbBi targets with HOO-MeVprotons.1 We are developing a novelprocedure to separate seleniumisotopes from the RbBr target mate-rial.

The process is based 01; the elec-trolytic deposition of the selenium as<".'.•.'') selenide fro;. .1 --.*'"•''• .1 con-taining a C .( h ) ion and seleniousacid onto a platinum-gauze elec-trode. A strongly adherent precipitateof Cu( I) selenide is produced. Vir-tually qt-antiiaiive deposition i: >bserved after 1 h; however, severalplate/strip steps are requited to remove trace radiochemical impurities.The final product contains approx-imately equal quantities of "\Se and7iSe and is suitable for generator development. We usually produce 200-to 300-mCi 'Se from a 2-day irradia-tion of a 30-g RbP>- target, with anoverall recovery of ~80%.

The success of the electrolyticseparation process suggests a novelapproach to the construction of a72Se/72As generator system. In de-veloping the separation process weobserved that arsenic does not de-posit to any appreciable extent underconditions necessary to depost Cu( I)selenide. Thus it should be possibleto develop an electrochemical gen-erator system that would be relativelysimple to use. One such system cur-rently under investigation involvesconcentric cylindrical platinum-gauze electrodes. By reversing thecurrent on these electrodes a scriesof plate/strip operations should re-lease the 7<:As to the solution of elec-trolyte. This system is currently beingtested and results are promising.

Reference

1. P. M. Grant, D. A. Miller, J. S. Gilmore, and H. A. O'Brien, Jr., "MediumEnergy Spallation Cross Sections. 1. RbBr Irradiation with HOO-MeVProtons," InternationalJ011 rnal of Applied Radiation and Isotopes 33, 415(1982 ) .

192

RESEARCH

The goal of Our research is to develop methods ot attaching radionuclides to monoclonal antibodiesand antibody fragments lor n.se ini.imor imaging and mu*rnal radiationtherapy Monoclonal antibodies andtheir fragments are of interest be-cause they enable (he selectivetargeting ot tumors. The labeled amibodies could be used as carriers totransport radioisotopes to tumors,'thus minimizing total-body radiationdose and radiation damage to normaltissue. We have developed methodsto label antibodies with1"1 Cu, a potentially useful medical radioisotopehaving a suitable half life (62 h) andnuclear decay properties" for use intumor imaging and therapy. Thisradioisotope is produced in highspecific activity ( 1~ ooo Ci/g) at1AM FF. Porphyrins were chosen as6~Cu chektting agents to be con-jugated to antibodies for two reasons:

(1) metalloporphyrins, which areubiquitous in nature, present littleproblem of toxicity and (2) copperporphyrins are very stable to loss ofcopper ions in human serum undersimulated in vivo conditions.' Wehave adopted the synthetic strategy otcoupling activated chelating agents,N-benzyl porphyrins, to antibodiesbefore labeling with h"C.u. This hasthe advantage of being a "cold kit," apurified porphyrin-antibody preparation that can be radiometalated asthe final step in the synthesis.

Radlophannaceiitical LabelingResearch

Preparation of RadiolabeledMonoclonal Antibodies

D f.'lcodv (Group if K. ' ! ; •..''". •'•Linn-"

RESEARCHvoai.c!:

Radiometalation of N-BenzylPorphyrins

j A Mercer Smith, 8 D Figarci. \A ••i

" iew • ori- .' Hijnter C allege and L os

The remarkable ability ofporphyrins to retain bound copperions and the great stability thrusynthetic porphyrin ring systemshave against degradation makethem desirable chelators of 67Cu forantibody labeling. There are twopossible strategies to radiolabel anti-bodies with 67Cu using porphyrins:

1. Radiome'alate the porphyrinfirst, purify the copperporphyrin, and then covalentlylink the metalloporphyrin tothe antibody. This method pres-ents the usual difficulties thatare inherent whenever short-lived radioisotopes are used.

2. Attach the porphyrin to the anti-body, then purify theporphyrinantibody conjugatebefore radiometalation of theporphyrin. This strategy has theadvantage of being a cold-kittype of synthesis in which radio-labeling is the final step of thepreparation.

We are investigating the secondstrategy as a means of preparingradiolabeled antibodies. A majordrawback to the use of porphyrinshas been the slow rates at which therelatively inflexible planarporphyrins incorporate metal ions.Although CuOl) is one of the most

rapidly incorporated metal ions, therate in aqueous solutions in the pHand temperature range where pro-teins are stable is too slow to makethe reactions of 67Cu with porphyrin-antibody conjugates feasible. Theonly route available for typicalporphyrins is the synthesis of the 67Cucomplex in refluxingdimethylformamide andpurification,4 followed by couplingof the radiolabeled porphyrin com-plex to the antibody (strategy 1). Toachieve the rapid metal-complexa-tion rates that are necessary for a pro-cedure in which a prepurifiedporphyrin-antibody adduct could belabeled with 67Cu immediately beforeuse, the porphyrin itself must besynthetically modified.

Lavallee5 has previously shownthat N-substitution of syntheticporphyrins of the weso-tetraaryl typeleads to greatly increased metal-com-plexation rates and that the rate isespecially favorable forCu(II). Oncethe Cu(II) ion is bound, the N-substi-tuent must be removed to give ahighly stable porphyrin complex be-cause metal ions are readily removedfrom the N-substitutedmetalloporphyrins.6 Simple N-substi-tuents such as the methyl group arenot removed by water as anucleophile under mild conditions,but require such strong nucleophilesas amines.7 The strong nucleophilesnecessary to remove the N-methyl

\')-t

RESEARCH

Hadioisolope Production

substituent require reaction conditions too harsh to be used forporphyrinantibody conjugates; how-ever, N-benzyl substituents are easilyremoved."The rate for the overallreaction of metal complexation andN-henzyl group removal in bufferedaqueous solution is rapid and independent of Cut II) concentration.9

For this study we selected watersoluble, N-benzyl-substitutedporphyrins that can be readily cou-pled to antibodies. Because the cou-pling of a carboxylate to an amine siteon a protein is a common strategy forantibody conjugation reactions, weexamined two N-benzyl porphyrinswith carboxylic acid functionalities.These two porphyrins are N-benzyl-5,10,15,20 tetrakisU-carboxyphenyl) porphine, denoted NbzHTCPP, and N-4-nitrobenzyl-5(4-carboxyphenyl)-10,15,20-tris(4-sulfophenyl) porphine, denoted N-bzHCSjP.

The four carboxylate groups of theN-bzHTCPP molecule present thepotential problem of crosslinking toamine groups on the antibody. Be-cause several identical carboxylategroups are available, crosslinking be-tween antibodies or multiple attach-ment on J single antibody is possible.Therefore we decided to include inour studies a synthetic Nbenzylporphyrin, N-bzHCS3P, thatwould have several peripheralanionic groups to provide watersolubility, but only a single carboxy-

late among them that could be usedfor coupling. We have described thesyntheses of these compoundselsewhere.'

In aborate buffer at pH 8.0, theprogress of the reaction of Cu (11)with N-bzHTCPP can be followedspectrophotometrically. With theporphyrin concenration at 10"'' to10~3 M and Cu(II) concentrationsfromstoichiometric to 10~J M.thehalf-life for the reaction at 40" C isless than 5 min and is independent ofCu(II) concentration, demonstratingthat metal complexation is faster thandebenzylation. With 67Cu at less than10"6 M (no carrier added) and otherconditions as above, ion exchangeafter separation shows that 95% ormore of the 67Cu is incorporated after10 min.

The results with coldCu(II) anduncoupled N-bzHTCPP support ourresults, which indicate rapid bindingof67Cu to porphyrin-antibody ad-ducts. Thus the N-benzyl porphyrinscanbemetalatedwith67Cu readilyunder conditions that do not de-nature proteins. Therefore, the at-tachment of N-benzyl porphyrins toantibodies followed by rapid metala-tion with radiocopper appears to be avery promising method to radiolabelantibodies with copper.

195

RESEARCH

- aa'

Coupling Porphyrins toAntibodies for Radiolabelingwith Copper-67

We are developing methods to at-tach porphyrins as chelating agentsto antibodies that retain the antigen-binding capacity ot the antibody.Copper-67, a radioisotope with a half1 ife and nuclear decay propertiesparticularly suitable for tumor imag-ing and therapy, is clvlated verytightly by porphyrins. If antibodiescan be labeled with'rCu while retain-ing their immunologicul activity,they would have great potential asagents for transporting of the copperisotope to cancerous tissue withminimum radiation damage to nor-mal tissue.

The two porphyrins we have usedareN-benzyl-5,10,15,20-tetrakis(4-carboxylphenyl) porphine, denotedN-bzHTCPP, and N-4-nitrobenzyl-5-(4-carboxyphenyl)-10,15,20-tris(4-sulfophenyl) porphine, denoted N-bzHCSjP, The N-benzyl group oneach porphyrin permits rapid metala-tionof the porphyrin under very mildconditions that are compatible withantibody integrity. The carboxylategroups on the N-benzyl porphyrinscan be used to form a covalentlinkage to antibodies. In addition tothe possibility of crosslinking of theantibody by the coupling reagentsused, the potential to preactivatemore than one carboxylate andsubsequently to crosslink the anti-body with the porphyrin exists withthe NbzHTCPP. This problem wasaddressed by examining the same

conjugation reactions for N-hzHCS^Pwith its single carboxylate. In allcases when crosslinking was ob-served with the Nb/.HTCPP,substituting the N-bzHCS,!' underidentical conditions eliminated thecrosslinking.

The porphyrin-antibody systempresents problems for the analysis olporphyrin-coupling reactions. First,porphyrins have an inherentnonspecific affinity for proteins ingeneral,10 the "sticky-porphyrin"problem. Second, copper has its ownaffinity for protein, and this is thebasis for the Biuret reaction, a stan-dard protein assay." Gel filtration byhigh-performance liquid chromato-graphy (HPLC) cannot separatenonspecifically bound porphyrinfrom the antibody and antibodyporphyrin conjugates. HPLC was alsoinadequate in removingnonspecifically bound copper fromthe antibody when 67Cu was added tometalate the porphyrin after cou-pling. A different method of analysiswas needed.

We developed sodiumdodecylsulfate polyacrylamide gelelectrophoresis12 as an analyticalmethod that removes all thenonspecifically associated porphyrin.Gel-scanning spectroscopy at wave-lengths appropriate for either protein(280 nm) or porphyrin(405/435 nm) permits accuratemeasurement of the porphyrin covalently attached to the protein aftercompletion of the eiectrophoresis,

RESEARCH

\ 'rorluction

Thus the use of a rtcliotracer is unnecessary. Gel nitration at very slowtechniques was also developed torpreparative scale purification of theconjugates and tor the removal <>tnonspecilically bound copper. Thelatter is o! importance lor the preparation ot porphyrin antibody conjugate kits that can lie easily labeledwith short lived isotopes by hospitalpersonnel for clinical use.

The porphyrins we are studyinghavecarboxylate tunctioi.al groups;consequently, we have examined reagents commonly used to form amidebonds between carboxylate andamino groups. The first reagent to bestudied was 1 ethyl 3 (3-dimethylamino propyl)carbodiimide hydrochloride(EDAC), a water solublecarbodiimide. We also examined Nhydroxysuccinimide used in conjunction with EDAC (NHS/EDAC).The third reagent we tested was apeptide synthesis reagent, 1,1'carbonyldiimidazole (CDI). Becauseall these reagents react with carboxy-late function groups on the proteinas well as those on the porphyrin, wehave used one basic strategy in ourattempts at conjugation. Theporphyrin is first preactivated withthe coupling reagent before the addi-tion ot the antibody. The antibody isthen added to the reactive intermediate, the preactivated porphyrin,and allowed to couple to the protein's amino groups, which are pri-

marily lysine residues.Reaction with EDAC proved to be

unsuccessful. A study ot theNHS/EDAC reaction as a function ofpreactivation lime, preaciivation pH,coupling time, coupling pH, and reagent concentrations gave an optimum coupling yield of 22% (average of 2.2 porphyrins/antibody) fornon-cross-linked N bz.HTCPP antibody conjugates. Under identicalconditions, the N b/.HCS,P had anoptimum coupling yield of 20% (av-erage of 2.0 porphyrins/antibody) innon-cross-linked conjugates, andcrosslinking was eliminated. Asimilar study for CDI gave an op-timum coupling yield of 30% (aver-age of 3 porphyrins/antihody) tornon-crosslinked N bz.HTCPP antibody conjugates. Similar conditionsgave a yield of 15% (average of 1.5porphyrins/antibody) for N-bz.HCS,Pantibody conjugates.

We have shown that N-henzylporphyrins can be attached co-valently to antibodies, and we havedeveloped methods to quantify theamount coupled. The ease of radio-metalation of the N benzyl porphyrinwith 67Cu both before and after con-jugation has been demonstrated. Ourfuture work will determine the effectthe coupling reactions have on theantigen-binding capacity of theporphyrinantibody conjugates whileexamining the possibility of usingother conjugation methods.

197

RESEARCH

Radosotope P: eduction

References

1. D. E. Yelton and M. D. Scharff, "Monoclonal Antibodies: A Powerful NewTool in Riology and Medicine," Annual Review of Biochemistry 50,657(1980).

2. S. Raman, andj. j . Pinajian, "Decay of 67Cu," Nuclear Physics A131, 393(1969).

3. J. A. Mercer Smith, S. D. Figard, Z. V. Svitra, S. M. Fehrenbach, and D. K.Lavallee, "Techniques of Radiolabeling Antibodies with Copper-67Utilizing Forphyrin Chelators," Los Alamos National Laboratory docu-ment LA-UR-85-3748, proceedings of the Radiochemical Labeling andCharacterization of Proteins Symposium, Society of Nuclear MedicineAnnual Meeting, Houston, Texas, May 31-June 5,1985 (in press).

4. J. A. Mercer-Smith, R. Scott Rogers, N. J. Segura, andW. A. Taylor,"Synthesis of 67Cu m&soTetra(4-Carboxyphenyl) Porphine for Conjuga-tion to Monoclonal Antibodies," Los Alamos National Laboratory reportLA-10366-PR (April 1985), p. 69.

5. General Mechanism of Prophyrin Metallation," Inorganic Chemistry 18,3358(1979).

6. D. K. Lavallee and A. E. Gebala, "Facile Dissociation of a CopperPorphyrin: Chlorocopper (II) N-Methyltetraphenylporphine," InorganicChemistry 13,2004 (1974).

7. D. KuilaandD. K. Lavallee, "Kinetics and Mechanisms of Reactions of N-Alkylporphyrin Complexes 3: The Effect of Porphyrin Ring Substituentsand Reaction Media," Inorganic Chemistry 22,1095 (1983).

198

RESEARCH

Radioisolope Production

8. D. K. Lavalleeand D. Kuila, "Kinetics of Dealkylation Reactions of N-Alkylporphyrin Complexes 4: Effect of the N-Alkyl and N-Aryl Substituents on the Dealkylation Process," Inorganic Chemistry 23, 3987(1984).

9. D. K. Lavallee, K. Liddane, A. Diaz, D. Mansuy, andj. P. Battioni, "N-Benzylporphyrins as Precursors for the Papid Synthesis ofMetalloporphyrins" (submitted to Inorganic Chemistry).

10. G. R. Parr and R. F. Pasternak, "The Interaction of Some Water-SolublePorphyrins and Metalloporphyrins with Human Serum Albumin,"Bioinorganic Chemistry 1, 111 ( 197"7).

11. A. G. Gornall, C. J. Bardawill, and M. M. Davis, "Determination of SerumProteins by Means of the Biuret Reaction," journal of BiologicalChemistry 177, 751 (1949).

12. U. K. Laemmli, "Cleavage of Stiuctural Proteins During the Assembly ofthe Head of Bacteriophage T4," Nature (London) 227,680 (1970).

199

RESEARCH

Ratiloisofope ProductionPublications

Publications (INC-3)

K. E. Peterson, M. A. Ott, 1". H. Seurer, N.J. Segura, W. A. Taylor, J. W. Barnes,F. J. Steinkruger, K. E. Thomas, and Philip M. Wanek, "INC-3 IsotopeProduction Activities in FY 1984," in "Isotope and Nuclear ChemistryDivision Annual Report FY 1984," Los Alamos National Laboratory reportLA 10366-PR (April 1985),pp. 66 69.

J. A. Mercer Smith, R. S. Rogers, N.J. Segu>-!, and W. A. Taylor, "Synthesis ofCopper-6? meso Tetra (i Carboxyphenyl) Porphine for Conjugation toMonoclonal Antibodies," in "Isotope and Nuclear Chemistry Division AnnualReport FY 198 i," Los Alamos National Laboratory report LA- IO366-PR (April1985), pp. 69 " 1 .

P. M. Wanek, Z. V. Svitra, R. S. Rogers, and W. A. Taylor, "Imaging andBiodistribution Capabilities at INC-3," in "Isotope and Nuclear ChemistryDivision Annual Report FY 1984," Los Alamos National Laboratory reportLA-10366-PR (April 1985), pp. 76-77.

P. M. Wanek and F.J. Steinkruger, "Rubidium-86 Production," in "Isotopeand Nuclear Chemistry Division Annual Report FY 1984," Los Alamos Na-tional Laboratory-report LA-IO366-PR (April 1985), p. 73.

F.J. Steinkruger, P. M. Wanek, and D. C. Moody, "Cadmium 109 — Silver 190mBiomedical Generator," in "Isotope and Nuclear Chemistry Division AnnualReport FY 1984," Los Alamos National Laboratory'report LA 10366 PR (April1985), pp. 73-75.

M. A. Ott.J. W. Barnes, F. H. Seurer, N.J. Segura, W.A.Taylor, H. A. O'Brien,Jr., and D. C. Moody, "Improved Targeting System for l23Xe — 123I Productionand Recovery," in "Isotope and Nuclear Chemistry Division Annual ReportFY 1984," Los Alamos National Laboratory report LA-10366-PR (April 1985),pp. 71-72; and , "New Stringer and Targeting System for 123Xe —* 123IProduction and Recu.'ery," in "Progress at LAMPF," Los Alamos NationalLaboratory report LA-10429-PR (April 1985), p. 139.

K. E. Thomas, N.J. Segura, andj. W. Barnes, "Isotope Separations from a ZnOTarget," in "Progress at LAMPF," Los Alamos National Laboratory reportLA-10429-PR (April 1985), p. 139.

F.J. Steinkruger, P. M. Wanek, and D. C. Moody, ""'9Cd — ")9mAg BiomedicalGenerator," in "Progress at LAMPF," Los Alamos National Laboratory reportLA-10429-PR (April 1985), pp. 143 H i .

200

RESEARCH

i viiiiuisotope Production

I, A. Mercer Smith, N.J. Segura, F.J. Steinkruger, Z. V. Svitra, W. A. Taylor, andP. M. Wanek, "Synthesis and Biodistribution of Copper-67 meso-Tetra (4-Carboxyphenyl) Porphine," in "Progress at LAMPF," Los Alamos NationalLaboratory report LA• 10429-PR (April 1985), pp. U5 Ub.

J. A. Mercer Smith, S. D. Figure!, and D. K. Lavallee, "Reactions to ConjugatePorphyrii.s ro Antibodies," in "Progress at LAMPF," Los Alamos NationalLaboratory report LA-MM29 PR (April 1985), pp. I46.

Z. V. Svitra, R. S. Rogers, and D. S. Wilbur, "Synthesis of Small MoleculesLabeled with Bromine-"'"'," in "Progress at LAMPF," Los Alamos NationalLaboratory report LA 10-i2l) PR (April l l)85),pp. I 1 6 \ r .

P. M. Grant and P. M. Wanek, "Radiation-Induced Redox Speciation ol'^Br inAqueous Solution as Determined by Anion Chromatography," Los AlamosNational Laboratory document LA-LIR-84-3868 (submitted to RadiocbimicaAda).

J. A. Mercer Smith, A. Raudino, and D. C. Mauzerall, "A Model of the Origin ofPhotosynthesis III. The Ultraviolet Photochemistry ot'l Iroporphrinogen,"Photochemistry and I'hotobiology 42, 239-2-44 ( 19H5).

J. A. Mercer Smith, S. D. Figard, D. K. Lavallee, and Z. V. Svitra, "Techniquesof Rudiolabeling Antibodies with Copper-6"7 Utilizing Porphyrin Chelators,"Los Alamos National Laboratory document LAUR-85-536 (submitted to theJournal of Nuclear Medicine).

F.J. Steinkruger, P. M. Wanek, and D. C. Moody, "Cadmium 109/Silver-109mBiomedical Generator," Los Alamos National Laboratory document LA-UR84-4O29 (submitted to the Journal ofNuclear Medicine).

F. T. Avignone, III, W. C. Barker, H. S. Miley, H. A. O'Brien,Jr., F.J.Steinkruger, and P. M. Wanek, "Near Threshold Behavior of Pair-ProductionCross Sections in a Lead Target" (submitted to Physical Ren air A).

M. D. Hylarides, P. L. Buksa, F. A. Mettler.and D.S.Wilbur, "Radiobromina-1 ion o!" 1 he I Position of Kstradiol Using No Carrier Added Bromine-""',"

Journal of Labelled Compounds and Radiopbarmaceuticals 22, 437 (1985).

201

RESEARCH

.V. o. Hylarides, A. A. Leon, F. A. Mettler, and D. S. Wilbur, "Radiolabeling ofthe B- and C Ring of Estradiol Using No-Carrier-Added Bromine-77,"/o//r«fl/of Labelled Compounds and Radiopharmaceuticals 22,443 (1985).

M. Speranza, C. Y. Shiue, A. P. Wolf, D. S. Wilbur, and G. Angelini, "Re-giospecific Rauiofluorination of Arylpentafluorosilicates as a General Routeto Fluorine-18-Labeled Aryl Fluorides," Journal of the Chemical Society,Chemical Communication 21,1448 (1984).

D. S. Wilbur, S. R. Garcia, M. J. Adam, and T. J. Ruth, "An Evaluation of theIntroduction of Stable Nuclides of Bromine into High Specific ActivityRadiobrominations," Journal of 'Labelled Compounds and Radio-pharmaceuticals 21,767 (1984). •

D. S.Wilbur and Z. V. Svitra, "Electrophilic Radiobrominations of HippuricAcid: An Example of the Utility of Afyltrimethylsilane Intermediate, Journalof Labelled Compounds and Radiofibarmaceuticals 21,415 (1984).

D. S. Wilbur, "Structural Determination of Some Chloroazepine 2,5 dionesUsing a Lanthanide Shift Reagent," Journal of Heterocyclic Chemistry 21, 801(1984).

M. D. Hylarides, A. A. Leon, F. A. Mettler, and D. C. Wilbur, "Synthesis of 1hromoestradiol," Journal of Organic Chemistry 49, 2744 (1984).

Patents (INC-3)

H. A. O'Brien, Jr., J. W. Barnes, W. A. Taylor, K. E. Thomas, and G. E. Bentley,"Method of Producing 67Cu," U.S. Patent No. 4,487,738, December 1984.

P. M. Wanek, F. J. Steinkruger, and D. C. Moody, "Biomedical SilverlO9mIsotope Generator," patent submitted, 1985.

202

RESEARCH

THEORY

Nonanalog Plon Double ChargeExchange Through the \,3 NueleonInteraction

•• , ' > ' • i • ! .

Double-charge exchange ( DCX )cross sections were calculated withina distorted-wave impulse approxima-tion framework.' The transition density was constructed microscopicallyfor transitions between specific shellmodel configurations. The reactiondynamics suggested by the data isDCX through the A,, resonance, asshown in Fig. 1 A model ot the torceincluding Jt + p exchange was used.

Results for the angular distribution( Fig. 2) and energy dependence ofthe 0" cross section ( Fig. 3) areshown. Although the magnitude ofthe 0" cross section dependssensitively on the range parameter ofthe pion-nucleon form factor, theangular distribution does not, suggesting that the A-nueleon interaction is the important physical medianism underlying the DCX.

Reference

1. R. Oilman, H. T. Fortune, M. B.Johnson, F. R. Siciliano, H.Toki, and A.Wir/.ba, Physical Review C 32, Vt9 ( 19KS ).

D

vt 10"

10"

80L .

1 40

. . 1 . •

200

FJMeV '

,'•'60

ih

Q

aner>

10°

] { ' ) - ' • '

10°

10-'

10""

10"'

10"''

I1J

lit] 1

1

1 lll

ll| 1

1

ITT

9

E

~"1

III

o

1

\

!

\

I20

T -I*Pk\

\

Bern

1 ' '1

200 J

164 "

\

120 "

}40 60

deg)

" ' ' A. di la t ions ol -c_)(7t ,7i ) -Me i>j :. !

several .-aiues of XK and Xp (vani^s

m Im"1) cont ras ted with data The •

labeled XK = 6 ' wvis calculated .-v

an intermediate p mesor i

tionsot 'flO(7i+.7t") lftNe(() s ; •: o'-^y.^-iwith angular distributions plotted oq,:-ir v.9C m m degrees Fhe calculation'", i,r>ed X"- Xp = 5 2 fm~' The incident pn'ir onprq ,T, (MeV) 'S denijtod beside each ;_ur ,e

2(U

RESEARCHI h('d>.

It has been recognized thai ther|(>iH) meson plays almost no role intraditional nuclear -structure physics1

because the r\X.\ coupling constantis very small" when compared withthe TLY.Yand n.S'A coupling constants.The situation, however, is quite dif-ferent in medium and high energynuclear reactions where r) producnon becomes possible. In arecent LAMIT experiment.* a significant amount ot pion inducedT| production in 'Heand IJC has beendetected at pion kinetic energiesnear ^oo MeV. A recent theoreticalmodel"1 for TI,V — r\i\' reactions indicates that threshold pionicT) production on a nucleon proceedsmainly through the formation of the.V* ( L S^S ) resonance and that ther|.\W* coupling constant is not small.Production of the r\ meson has alsobeen observed in proton nucleus col-lisions at proton kinetic energies of— 1 GeV. In addition, experimentalevidence of ft" r)'' mixing in nuclearreactions has also been reported.s

Clearly, medium-energy nuclear reactions create new opportunities forstudying the interaction between anucleon and the short lived( — |ir'"-si r\ meson.

The work of Bhaleraoand Liu' indicates that the realistic r(,V —- r\X interaction, which is compatible withthe KS — rjiVdata, is attractive at low-energies. \X e have used the model ofKef. t to generate an r| nucleon andthen a c< 'variant r|-nucleus optical po-tential Our result is that this opticalpotential can lead to the formation ofnuclear bound states of the r| meson.6

Because the T| has no electric charge,these bound states of TJ are notcaused by the Coulomb force. Theyare solely the result of the stronginteraction between the r| meson andthe nucleons in the nucleus. In thesebound systems, which we call r\mesic nuclei, the r| meson is boundin a nuclear orbit.

In Table I we present thepredicted bound-state levels in vari-ous nuclei.6 These bound states areobtained with full (.«-, /)-, and c/wave)r|A' interaction as well as with I'Vrmi-averaging over the nucleon motion.In our full off-shell calculation, all

Theoretical Evidence «or theExistence of the ii-Me&Sc NucleusQ Haidei and L C Liu (Los Alamo?.)

T ie Bmclmq fcnerqies and H311 u iciths (m Millions oi Election volts) ol T|UPSIC N.iciei Trie parameter sets and II mter to the parameters ol Rel 4jHtein-imecl iiom the nN phase shilts ol Amdt anrl tho C'FRN 'heoret'cal

:oeDh

subthreshold r|.'V interactions enter(see Ref. 6 for details). From Table Iwe see that the r|-mesic nucleus canexist for nuclei ranging from I2C to™Pb. The fact that a nucleus of suffi-cient size is required to developbound states, which are absent in

Set I)

—! _? 68 + c- 99/)- ( 1 3 "4 + 9 b'ii)—j .] 38 4- 6 H9/i

- i i : 2 ' + 9 T2i)

- I 5 1 2 + 6 390

- I if) 44 + ~ ! I.)

— i 4 ' 0 + t;. ' ";)

- i ' •'-. + i bOi)

- ( 19 7-l + H ? 1')- ( 0 9[i + b 44; i- i ! ' 82 + 9 M ,)- ( 9 '<) + 6 44.)

- ( 1 4 86 + 9 39')- ( 3 5 4 + 5 80/)

- ( 8 38 + 6 63/)

- ( /' hh + 4 55,)

- ( 0 ;-"tj + Z1 9fi;)

205

RESEARCH

Theorv

few-nucleon systems, is easily under-stood from basic quantum mechani-cal principles.7

It is instructive to compare thebinding energies of r)-mesic nuclei.win those of A hypernuclei.This isdone in Fig. 1, wher* we show theA dependence of the predicted binding energies of the lx state:-, of the TImesic nuclei (solid circles) togetherwith the extrapolated A dependenceof the A-hypernudei bindingenergies8 (dashed curve). We notethat the difference in the bindingenergies, (B.E.)A — (B.E.)V is nearlyequal to half the separation energy ofthe nucleons in these nuclei. Thisdifference can be qualitatively under-stood from the fact that a A hyper-nucleus is formed after con-

verting an already bound neutron,whereas to form an Tj-mesic nucleusthe T] meson has to be captured into abound orbit.

We have further noted that only thei-wave r\N interaction is important.Fauli blocking and the density-square dependent interaction havevery small effects on the calculatedbinding energies and widths. Devia-tions of measured binding energiesand widths from the predicted ones,therefore, could be due mainly to themedium effects on other dynamicalquantities such as the self-energies ofthe T|.

As the work continues we shallextend our calculations to identifythe experimental signatures of T|-mesic nuclei.

g E

nerg

y (M

eV)

Bin

din

30

20

10

(

i r— i i , , ,

s

_ -v

•

, . . . 1 1 1

) 0,05

1 1 | 1

• * •

0

i l l .

0.10

A - 2 / 3

> i i ; i i

A Hypernuclei

t n Mesic Nuclei

0

. . . 1 i .

0.15

1 '

-

-

020

FIGURE 1 The 4 dependence ol the binding energies ol the 1 s-state r|-mesic nuclei(solid circles) and of the A hypernuclei (dashed curve) The Tj-mesic nuclear-bindingenergies are the set I results ol Table ! The A-hypemuclei binding energies areextrapolated Irom those determined m light nuclei by using the formula given in Ref 3

206

RESEARCH

Theory

References

1. H. Filkuhn, The Interactions of Hadrom(North Holland, Amsterdam,

1967).

2. W. Grein and P. Kroll, Nuclear Physics A338, 332 (1980).

3. J. C. Peng et al., AIPConference Proceedings 133, 255 (1985).

4. R. S. Bhakraoand L. C. Liu, Physical Review Letters 54, 865 (1985).

5. P. Berthet et al., Noiivelle de Satnrne ( Laboratoire National Saturne,Saclay, France, 198-j), Vol. 9A, p. 28.

6. Q. Haider and L. C. Liu, "Formation of Eta-Mesic Nucleus," Los AlamosNational Laboratory document LA-UR-85-3361 (submitted to Physics Let-ters B).

7. L. 1. Schiff, Quantum Mechanics, 3rd ed. (McGraw-Hill, Tokyo, Japan,1968).

8. B. Povh, Annual Renew .-v'Nuclear and Particle Science 28,1 (1978)

207

RESEARCH

h Self-Consistent Calculation ofOne-Gluon Exchange in theFrledbers-Lee Sollton Model

': A

_ -1/-

Ay—

AI*—*il7t

P0)

•'*• ass->s a r ° rs'

2a •_ . rated

: !

ec^-d"

E-o-^

i i

r.-.ei

' °,

:; :.

It is well known that st.u-c bagmodels1"1 have been relatively suc-cessful in reproducing the spectraand properties of low lying hadronicstates involving light quarks (up,down, and strange). A central dif-ficulty with all such models is thehandling of the dynamics of the con-finement mechanism. A field theo-retical approach to this dynamics hasbeen formulated by Friedberg andLee in their nontopological solitonbag model.3

Numerical solutions to theFriedberg-Lee model involving onlyquark and scalar fields have been ob-tained by many authors.4'7 The modelwas first applied to the nucleon andthe delta by Goldflam and V-'ilets.8 Itwas later extended to the study ofmesons by Celenza et al.9 In all thesecalculations4 9 the exchange ofgluons between the quarks wasneglected.

The effects of one-gluon exchange(OGE) have been investigated re-cently by Bickeboller et al.10 In theirwork the gluon field is treatedperturbatively to lowest order in thestrong-coupling constant a,. The ef-fects of OGE on hadron masses havealso been studied by the MIT groupusing a perturbative approach.1 Theperturbative OGE assumes that theinterior of the bag belongs, presum-ably, to the region where asymptoticfreedom holds; consequently, thegluonic interactions can be treatedperturbatively. However, there is noconvincing argument to support theidea that the asymptotically free re-gion is indeed attained everywhereinside the bag, which can have a

spatial extension as large as 1 to 2 fm.Furthermore, the effective strong-coupling constant, as determinedfrom perturbative calculations ofOGE,11" is rather large ( ~ J ) andtherefore should cause concernsabout the soundness of evaluatingOGE perturbatively.

Over the past year we have de-veloped a self-consistent procedurefor calculating OGE effects in theFriedberg-Lee model."1" This proce-dure takes into account the iterationof OGE to all orders as opposed tothe more commonly used first-orderperturbative calculations. The proce-dure developed by us is quite generaland can be easily adapted to otherbag models.

TABLE il Magnetic Moments (in Units ofNuclear Magnetons) ol theBaryon Octet Calculated withthe Parameters Listed mTable I

Particle

Pn

A0

I +

1°I~=•0

Calculated

2 62- 1 74- 0 55

2 570 79

- 1 02- 1 40- 0 50

Experiment

2 79- I 91- 0 61

,•' 38

- 1 10- I 25- 0 69

In Table I we present our resultsfor the ground-state masses of thebaryons (octet and decuplet) andmesons (pseudoscalar and vectornonets). The most striking feature ofthe self-consistent calculation is theprediction for the pion mass(~117 MeV). It should be men-tioned that the perturbative OGE cal-

dilations''12 predict the pion mass tobe ~3S() MeV.

In Table il we present the resultsfor the magnetic moments of thebaryon octet and compare them withthe available experimental data. Ourpredicted value of g,/gv for theproton is 1.() 1, to be compared withthe experimental value ot 1.25. Because chiral symmetry and other re-lated dynamics have not been takeninto account in our calculations, weconsider the level of agreement be-tween our results and the data quitesatisfactory.

In Fig. 1 we compare the measuredproton and pion form factors with thetheoretical predictions. It is worthnoting that a self consistent treatment ot OGE improves considerablythe calculated form factors formomentum-transfer q< 600 MeV/c,indicating that it represents a signifi-cant component of physics at lowmomentum transfer. The discrepancybetween the calculated form factors(perturbative and self-consistent)and the experimental data at verylarge q is of no surprise because thebehavior of the form factor at large qdepends on dynamics beyond OGEthat have not been considered in thiswork.

In conclusion, we believe that one-gluon exchange has to be treatedself consistently in quark modelsbefore applying these models to nu-clear physics.

RESEARCHTheory

1.0

0.5

0

1^ ^ Proton

\

\

i- \

Chargei

Form Factor

Self "Consistent— Perturbative

—

•

0.5

0

Pion Charge Form Factor

Self ConsistentPerturbative

• Data

?

0.5 1.0

q(GeV/c)

1.5

FIGURE i The measured proton and pion lorm lactors compared with the predictionsol the perturbative (Ret 1 2) and sell-consistent calculations

209

RESEARCHTheor,

References

1. T. DeGrand, R. L.Jaffe, K.Johnson, andj. Kiskis, Physical Review D 12,2060(1975).

2. AW. Thomas, Advances in Nuclear Physics 13: 1 (1983).

3. R. Friedberg andT. D. Lee, Physical Review D 18, 2623 (1978); and T. D.Lee, Physical Review D19,1802 (1979).

4. R. Goldflam and L. Wilets,/%5/ctf//?er/eu>,025,1951 (1982).

5. R. SalyandM. K. Sundaresan, Physical Review D29,525 (1984).

6. T. Koppel and M. Harvey, Physical Review D$l, 171 (1985).

7. L. R. Doddand M. A. Lohe, Physical Review D 32,1816 (1985).

8. R. Goldflam and L. Wilets, Comments on Nuclear and Particle Physics12,191 (1984).

9. L. S. Celenza, A. Rosenthal, and C. M. Shakin, Physical Review C31, 212(1985), and 31, 232 (1985).

10. M. Bickeboller, M. C. Birse, H. Marschall, and L. Wilets, Physical Review031,2892(1985).

11. Q. Haider and L. C. Liu, "The Effect of Self-Consistent Treatment of One-Gluon Exchange in the Friedberg-Lee Nontopological Soliton Model,"Journal of Physics (i (Letter) (in press).

12. Q. Haider and L. C. Liu, Los Alamos National Laboratory document LA-

UR-85-1360 (1985).

210

RESEARCH

Theory

I. Introduction

The pion nucieon interactionbelow 100 MeV has been a focalpoint of interest in hadronic physicsfor many years. For many the desirefor better data was motivated by thepossibility of being able to comparedata with the predictions of PCAC.More generally, however, this systemprovides a laboratory for testing, insome depth, our basic concepts ofhadronic interactions. The elec-tromagnetic coupling, through thephotoproduction and photoabsorp-tion reactions, is expected to play animportant role in this endeavor. Thisprogram has recently seen concreterealization with calculations of pion-nucieon scattering being performedin both meson exchange and QCD(cloudy bag) models.

The recent observation of the very-deep minimum in the 0 ° cross sec-tion for analog pion charge exchangefrom nuclei has given even more im-petus to research in this area. It wasfound that the position of this mini-mum was better known in tjfie nuclearcase than in free pion-nucieoncharge exchange. Of course only the7f"p—*-7r,°n reaction is directly ac-cessible in the laboratory while the;t+n— Jt"p cross section is needed toperform the nuclear calculations. Be-cause of the cancellations involved,methods must be used which takeinto account the necessary isospin-breaking corrections when trans-forming between the two systems.

For these reasons we have recentlyperformed an analysis of low-energypion-nucleon scattering withemphasis on the new charge-ex-

change data taken by Fitzgeraldetai.'atLEP.

Briefly, the technique employs athree-channel system of coupledpotentials. The three channels are vTp, 7t°-n, and y-n. For most of the analy-sis the third channel was not needed.The strong interaction part of thesepotentials was obtained from a rota-tion in isospin space of the diagonalI = 3/2 and I = 1/2 potentials. Usingthis method the specific effects of theCoulomb potential and the pion andnucieon mass differences were ineluded. These are important correc-tions at the low pion kinetic energiesconsidered here. The potentials arechosen to have a separable form:

e eV(r,r ' )=g — —

r r'

for each SJ channel, except the Pn ,which is taken to be the sum of twosuch terms. While this choice of po-tential form is directed toward ap-plication to the nuclear problem, thecodes employed are able to use anywell behaved nonlocal (or local) po-tential.

The results of this investigation areinteresting in several respects. First, acomparison is possible with existingTC+ and 7t~ elastic scattering data basedon the charge exchange data and theconservation of isospin (after theisospin breaking corrections men-tioned above have been removed).Our findings in this area are reportedin section II.

The Pion-Siucleon System at Low

W. R. Gibbs and P. B Siegel (LosAlamos)

"The presenl report is a summary oi a paper submitted lorpublication in Physical Review C. LA-UR-85-3915

211

RESEARCH

- 10

Q

Second, it is possible to use isospinconservation to determine (heK+n—*ir"p cross section, correcting forthe mass differences and Coulombeffects. We find significant dif-ferences between this cross sectionand the measured cross section,particularly with respect to thecancellation in the zero degree crosssection. These results are discussedin section III.

Finally, in section IV, the low-energy behavior of the s-wnve phaseshifts is discussed, and the value ofthe "odd" scattering length is ex-tracted. The relation to thephotoabsorption data can be seenand some insight into the reactionmechanism obtained.

II. Data Analysis

Since the 7r+-proton data is moderately self-consistent, we startedfrom conventional phase shifts forthis system. Even after some adjustments, our scattering parameters arevery similar to those found in theliterature" (Figure 1). Note that it wasthe strength and range of the isospin3/2 potentials that was actually ad-justed to give the fit to the data; wedeal with phase shifts only as an in-termediate step. By fitting theJiTp—*n°n charge exchange data,which consists ot the new forwardangle data of ref. 1 along with threeback-angle points3 and two inte-grated cross sections4, we were ableto obtain a fit with a xVN of the orderof 1. The isospin 1/2 potentials (andhence the corresponding phase

40 SO 00 70

Tn(MaV)ao oo too

oS

10 30 30 40 50 60 70 00 80 100 10 30 30 40 SO 00 70 OO 90 100

T.CMoV)

.>' 'J .". 3 ,

ohil is M t h wor ld data II was vended thai the use ol the do t ted o n ye tor F1-,, (ar

n I' j ior • j ! this work al though it does lead to a slightly bolter lit lor the K+U data

-p 'or /v3rr|

, i ! l t ' i m o I

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I hoory

a " " • - > i '. O H

M( !( ) '! !( I

- " ' - ' i t

shifts I were the only quantitiesvaried in the process. The resultingphase shifts are shown in Fig. 1, andthe potential strengths and ranges arelube found in the table. Most ot thesescattering parameters are consistentwith previous determinations.

A notable exception to this agreement is the Pn phase shift, which hasa less negative value than that usuallyascribed lo it. This result was forcedby the chaige exchange data, primar-ily the Fitzgerald data, by the limitedamount of spin flip cross section al-lowed. This has possible conse-quences with regard to the calcula-tion of pion true absorption, on thedeuteron especially, since it is thischannel which drives the process.Note that our analysis is valid only upt< > "I) MeV so the c.i >ssing point atys MeV ( Fig. 1 I cannot he considered meaningful.

We may now reverse the normalprocedure (using n+and n~ scatteringdata to calculate charge exchangecross sections) lo predict the K pelastic scattering. We find that ex-cellent agreement is obtained withthe three highest energies of theFrank ef.//. data" ( Fig. 2). This is

most interesting since when published, this data oVagrc ; J with theavailable phase shifts l.<. s> >.! on worlddata. On closer inspection we foundthat, in fact, only or t data set6 de-termined those low energy isospin1/2 phase shifts, and we concludethat this data6 is inconsistent with thecharge exchange data and isospinsymmetry, while the Frank data (atleast the three highest energies) isindeed consistent with these requirements.

On the other hand, the TC+ and n~scattering for the lowest energy (29.4MeV) Frank data appear to be in-consistent. Actually a stronger state-ment can be made: There appear tobe no strong phase shifts which canreproduce the three sets of data (thelow energy n^p elastic scatteringfrom ref. 5 and our chaige exchangedata base13'4) and still conserveisospin.

Frank n p

rjref;lir>p,-| PI

el al data'1

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III. The Charge ExchangeCross Section

Tht reactions nTp—• Ji"n and7t+n—*7t°p have a difference in Qvalue ot twice the neutron-protonmass difference. This difference (andthe Coulomb potential present in thefirst reaction) leads to a noticeabledisplacement in the position of the s-p interference minimum as can beseen (fig. 3), when plotted as a func-tion of pion laboratory energy. Notethat this causes a significant dif-ference in the 0° cross section for

100.0

70.0

50.040.0

30.0

20.0

10.0

7.0

5.0

3.0

2.0

1.0

1

= \

: \ ,

z \—

1

1

D —• K ' • n

i

%

i

//

i j

J1* ^ /i

KJJ

i

t

i

'//

Im—

|

1 I

/ / -/ /

'/ \—

;i~p — Jt'-'n(no mass difterences)

1 130 35 40 45

Tn(MeV)

50 5 5 6 0 65

The n~

.ird \*-

'-n and Tt+n—-TCOP zwo degree CJOSS sections obtained m thus A-ork

ith Oju-orsij ejects only is also included to demonstrate that mass

r-it~, |-,ritpntiai iftaa to oartiaily cancelling effects

energies as high as 55 or 60 MeV.The importance of knowing the

precise position of this minimum isthat the charge exchange reaction(n+n—*7t°p) in a nuclear environmentshows a remarkably similar behavior7.The existence of such a sharp featurein the nuclear reaction provides ahandle on possible medium correc-tions to the jt-nucleon t-matrix, eitherin the transition operator or in theremainder of the reaction mecha-nism. However, such a tool is usefulonly if the free space properties arewell understood.

An example of the importance ofthe free space information follows.THr minimum in the zero degreecross section for charge exchange onnuclei occurs at higher pion energiesas the mass number increases. Thisphenomenon can be understood interms of increasing Coulomb re-pulsion and greater Q-value forheavier nuclei. For the lightestnucleus measured however, 7Li, theminimum falls somewhat below thefree iCp—<-n"n minimum. We now seethat the minimum in the free7t+n—*7i°p reaction (the relevant com-parison) falls at lower energies, andthis fact presumably explains some ofthis displacement. The rest of theshift is probably due the attractivepotential seen by the pion due to thestrong interaction. The comparisonof the nuclear charge exchange withnucleon charge exchange providesus with an excellent way to test ourcalculations of the effective pion-nucleus interaction, but only if theposition of the "free" minimum isprecisely known.

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We present a polynomial approx-imation to these amplitudes whichgives a representation of our fits tothe data around the minimum(~-30-60 MeV). These amplitudeshave the form

fNF(8) = cos8

fSF(9) = f, s in9

a ( 6 ) = !<>( | f N F ( 9 ) | - + | f s l : ( 6 ) | 2 l

The functions, f, are given in fm andthe cross section is in mh/sr.

The coefficients are

Jt~p—*7i°nf0 = -0.1983 + 0.0810k- - 0.0068if, = 0.6554k"-.034k1+ O.4325ik'f, =0.38>6k- + ().2025iks

7r+n—7t"pf0 = -0.2000 + 0.0848k2 - 0.0054if, =()."()37k2-().ll9k4 + O.5Ol6ik5

f, = 0.3905k" + 0.241 liks

where k is the charged pion momen-tum in the center of mass in units offm"1. The amplitudes can also bewritten in a separable form:

where k' is the 7t" momentum in thecenter of mass, and \/s is the totalinvariant energy. In this form, the Xfunctions are nearly the same for thetwo systems.

IV. Low Energy Results andPhotoabsorption

It has heen known for many yearsthat the isospin 1/2 pionnucleon swave phase shift is not well repre-sented by a pure scattering lengthapproximation (i.e., it is not propor-tional to pionnucleon momentum)except at very low energies(<30 MeV)9. Until the recent chargeexchange data became available, thisenergy dependence had not beenmapped out in detail. In contrast tothe isospin 1/2 amplitude, the cor-responding isospin 3/2 phase shift iswell described by a scattering lengthapproximation, even at energies ashigh as 100 MeV. This can be taken asa direct indication that the interac-tion range of the 1/2 channel is muchlonger than that of the 3/2 channel.The present work makes this state-ment quantitative in terms of therange of the potentials needed to fitthe data. We will return to discuss theunderlying physics of this differenceat the end of this section.

By using the potentials obtainedabove and removing the mass dif-ferences and Coulomb effects torestore isospin conservation, we cancalculate the "odd" scattering lengthin a world in which isospin isabsolutely conserved. We obtain for

(= a - a 3 )

a = 0.290 ± .008 iT

[Fitzgerald]

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It'we use the three highest energiesof the Frank data to perlorm the corresponding, hm independent, analysis we obtain

a = n.2H-t ± .DOS n~'

[ Frank]

in complete agreement with thecharge exchange result. These valuesare also in good agreement with theresults (it many dispersion theoryanalyses.

There are several references in theliterature which quote values of "a"around 0.26 [i~l. Traditionally1' thecharge exchange and dispersion relations tend to give the higher number;7i~p elastic scattering and pionphotoproduction give the lowernumber. The result from Frank's datais clearly an exception to the 7t~pelastic "rule". Perhaps the previousdata did not extend to sufficientlylow energies.

An exception to the charge exchange "rule" is a recent value ob-tained by Salomon ft ill.'1 In extracting this result the authors assumed,however, that the scattering lengthlimit had been reached at 28 MeV. Ifwe use the energy dependence ob-tained from our analysis, we findagreement with their cross seel ion(in fact this data is included in ourcharge exchange data base). Itshould he clear that the energy de-pendence of the S{/1 phase shift (andhence of the charge exchange crosssection) is a crucial feature ol lowenergy 7t nucleon scattering.

A persistent discrepancy has ex-isted for many years beiween the oddscattering length obtained from pioncharge exchange and that obtainedwith the use of the l'anolsky ratio1", I1.In order to make this comparison onemust know the value of 1' and diezero energy limii i >l the cross sectionI'or7t~+p—MI+Y (with Coulomb el'fects removed ). In practice this limitis inferred from the principle ol tietailed balance, measurements of K(the ratio of Y+n—7i"+p toy+p—>7t"rn) from deuteron targets andthe extrapolation to zero energy olthe photoproduction cross section onthe proton. While there may be someproblem with extrapolating R to zeroenergy ( Coulomb and deuteron ef-fects must be removed) we will as-sume (along with ref. 10) that thenumber R = 1.3-1 ± .02 is correct. Thevalue of P is accurately known to be1.5-i6± .009"'.

The relevant photoproductioncross section is considerably less wellknown. The needed quantity is actu-ally the cross section with the phasespace ratio removed:

k= - a(YP—rc+n

q

In figure -i a' is plotted as a functionot pion momentum. The data is thatof Adamovich ft ,(/." The doitedcurve is their fit, based on apolynomial in pion momentum,which rep-esents these points andhigher energy data (which is primar-ily p wave ) as well. This extrapola-tion is essentially the same one used

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Theory

to get the zero energy value ot a'( 193 uh> em ploy eel in rel. 1 1 to oht a i n a , - a , = .2('3±.ni)TH"'.

The solid curve shows our calculation lor the cross section using arange of 2<><> MtA'/V for the V,, coupl-ing potential and a strength adjustedto give the correcr. I'anofsky ratio, Forthese low energy data points we ohtain a hetter x~/N [ '1;ln rt"'~- ' ' Notethat we lit the recently measuredpoint of Salomon er ;i/.'' at 2"\-i MfV.Since our calculations are s waveonly, and we have not performed amultipole analysis, our results may heslightly too high at q = .4 mi"1. Twodifferent analyses hy Berends a itl.'-(shown also in Figure i) have a verysimilar energy dependence hut aslightly smaller magnitude.

Another recent value of a' at zeroenergy is that of Noelle and lJteill(:223 uh. If we compare this with ourvalue of 232 ± 13 |ih. we note agreemem with their extrapolation of thephotoproductinn cross sections.

Our conclusion with respect to thePanofsky ratio is thai there is no discrepancy within the quoted errors(even not including errors in R) ifrecent photoproduction analyses,with a substantial energy dependence, are used.

This energy dependence is perhaps [he must interesting aspect oflow energy K nucleon scattering andpin iioprod net ion. We lincl thai itarises naturally !nmi the inclusion ota finite size fi >r the pion nucleon systern of the order of I fm. This lengthis a natural fundamental scale ol thepion nuclei MI system. We note that a71 nucleon scattering mechanism in

which the pion interacts with one ofthe pions in the pionic cloud of thenucleon can proceed, to a very goodapproximation, only through theI = 1/2 channel. This is hecau.se theTt-ji interaction at low energies ispredominately isospin zero (theI = 2 .scattering length is an order ofmagnitude smaller). Thephoioproduction reaction can alsoproceed directly via the pion cloud.Therefore, in this simple picture, theSj/2 and 7-N potentials would haveroughly the same range (about 1 fm,or a ~ 200 MeV) and hoth longerthan the I = 3/2 channel for which

p y\i—n+'<

0 /• I'! 4- ')

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Theoi •.

the 71-Tt interactions must go throughthe much smaller I = 2 interaction.Thus we might expect the 3/2 lengthscale to correspond to the confine-ment range or bag size.

To get some feeling for how therange is related to the energy dependence of the phase shift it is onlynecessary to consider the solution tothe separable potential problem. Ifthe potential has the form

V(r,r') = v(r')

then the scattering amplitude isgiven by

f(q,q',E) =X.v(q)v(q') D(E)

The factor D(E) is slowly varyingin this case so that the main energydependence comes from the momen-tum dependence of the functions v,i.e.,

f (k,k,E) ~ v(k)J 1

where a is the range of the potential.This analysis assumes that the systemis described by an energy independ-ent potential (i.e. that kis independ-ent of E) since there is no reason toexpect a strong energy dependenceon this scale.

The resultant picture is that of anucleon consisting of two compo-nents: one of long range and rich inpionic components and one of shortrange and containing primarily non-pionic components. While this pic-ture has often been consideredbefore, it is interesting to be led to italong a new route. The novel featureof this work is that the energy de-pendence of the S1/2 and S,/2 phaseshifts can be used to measure thespatial extent of these two compo-nents, allowing us to inferentiallyseparate quark and pionic degrees offreedom

218

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Theory

References

1 D. H. Fitzgerald ft al. To be published.

2. R A Arndt, SAID on line program Handbook of Pion-Nucleon Scattering,l-'ach information zentrum, Karisruhe.

3. .1. Duclos et al.. Phys. Lett. B43, 2-15 ( 19^3>.

-i. M. Salomon, D. 1;. Measday, J. M. Poutissou and B. C. Robertson, Nucl.l'hys. A414, 193 ( 198-1).

=.. J. S. Frank et al., Phys. Rev. D28, 1569 ( 19H3).

6. K. M. Crowe et al, Phys. Rev. 180, 1349 ( 1969).

~. F. !rom etal. LA UR-H5-2668.

S. Ci. Kallen, Elementary Particle Physics (Addison Wesley Publishing Co.,Inc. 19(vi, page KH.

9. Adamovith et al.. Soviet Journal of Nuclear Physics, 8, 685 (1969).

10. .1. Spuller et al.. Phys. Lett. 67B, -4^9 ( 197"7).

11. M. 1. Adamovich eta!., Sov. Jour. Nucl. Phys. 7, 36<> (1968).

12. F. A. Berends and A. Donnachie, Nucl. Phys. B84, 3-42 ( 1975).

l.V P. Noelle and W. Pfeil, Nucl. Phys. B31, 1 (1971).

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Report of She T-5 TheoretiGal Group Briefly summarized heiv arc a fewof the research topics consideredduring 19KS by members of the Mediuni- Energy Physics Theory Group(T-5) of the Theoretical Division atLos Alamos. These topics span a verywide range of subject matter, fromconventional low energy nuclearphysics to physics of direct interest toLAM IT and to problems that could beaddressed hvLAMl'F II.

Three-Body Forces in theTrinucleon System

Traditional nuclear physics hasbeen primarily an investigation ol applications of nuclear Hamiltonianswhich are nonrelativistic, entail onlypairwise (two body) forces, and ig-nore subnuclear degrees ol Ireedom.Such models have been relativelysuccessful in describing theproperties of nuclear ground states,as well as nuclear scattering and reactions. The implication is that forcesdepending upon the simultaneouscoordinates and quantum numbers ofthree nucleons (three body forces)are relatively unimportant. Suchforces are intimately linked lo iheDirac approach to proton nucleusscattering at intermediate energiesand may play a .substantial role in thestill not entirely understood spin orbit splittings in nuclei. Their small-ness, however, hinders our ellort toobserve three body force effects inmany-body systems, where we lackthe ability to generate accurate wavefunctions. Therefore, the trinucleonsystem plays an extremely important

role in the search for three bodyforce effects, because we are nowable to calculate numerically ac-curate solutions I'D; niMirelaiivisiicHamiltonians.

The three nucleon systemprovides (together with the a-par-ticle) nonirivial tests ot the tra-ditional model. There is no guaran-tee that a nucleon nucleon lorcemodel constructed to reproduce thedeuteron binding energy andnudeon-nucleon scattering phaseshifts can account for the trinueleonobservables. Indeed, systematic in-vestigation of the low energytrinucleon properties, which deter-mine the size and energy scales of the'H and 'He bound stales as well as thescattering of neutrons and protonsfrom deuterons, has revealed the in-adequacy of the pairwise force as-sumption. The benchmark solutionsot the Los Alamos Faddeev Grouphave demonstrated that "realistic"two-body force models underbindthe triton by approximately 1 MeV(out of H.S MeV), possibly indicatingthe presence of three-body forces.The corresponding theoretical 'l Icharge radius is too large by some tenpercent, and the (zero energy) neutron deuteron spin-doublet scattering length is too large by a lactor of 1.In addition, the Vie elastic electronscattering charge form lactor doesnot exhibit its first zero ai smallenough momentum transler, and thesecond maximum is not large enoughto explain the data.

Our recent nonperturbative, configuration-space Faddeev calcula-tions employing contemporary three

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body forte' models indicate thatthree niicleon forces may indeed beof sufficient size to bring the theoretical values of the low euerg\U'inucleon ohservabies into reasonable agreement with experiment.The modelling of the nuclear threebody force is in its I't.mcy, muchwork remains before three nucleonforce models will approach thesophisticate HI ot toil.'.\ s n.-.iti~.iunucleon nucleon lorce models.Nonetheless, utilizing cu'rent twopion exchange three nucleon(. 2TC-3N ) force models, we obtain anincrease in the triion binding energyor"roughly 1 S Me\' over that obtainedusing only a two body lorce. That is,•'H is slightly overb-uiiKi, with toosmall a radius, aiul the neutron deuteron scattering length is smallerthan the data would indicate. By varying model parameters, we have beenable to establish a simple relationship between the trinudeonbinding energy and the corresponding nns radius, and to confirm therelation t Phillip's Line) between the*H binding nenergy and the neutron-deuteron doublet scattering length.Calculation ol the trinudeon chargeform factors is still in progress.

It is clear trom our investigationthat ,1 more sophisticated threenucleon force model could correctthe underbindinL; of the triion. reduce the 'H and 'He charge radii tovalues in agreement with experiment. and lower the doublet neumm deuteron scattering length to itsmeasured value In addition, we haveestablished that first order perturbation theory is inadequate to obtain

even qualitatively reliable numbersfor the additional binding from thethree bod\ forces, that the nudeonnucleon odd purity partial waves contribute substantially to the wave lunclion when a three nucleon torce isincluded in the Hamiltonian (whichis not true for the two body forcecase ), and that all existing contemporary three nucleon force modelsrequire that a large number of threebody channels ( viz., Vi, all twonucleon potential components corresponding to partial waves withJ <H ) be included to ensure that '.hecalculation has produced a con-verged answer.

Pion Charge Exchange

The pion single and doublecharge exchange cross sections tromlight nuclei (in. particular, "C ) havebeen calculated. Using a three bodymodel (12C core plus 2 neutrons) or asemiphenomenological wave func-tion fit to (t,p) reactions, thequalitative features of the reactioncan be understood. A detailed examination of the model showssubstantial sensitivity to nucleonnucieon separations between i).*> and1.0 fin. This distance is such thatsome explicit quark effects might beseen for large hag sizes. No evidencefor quark degrees of freedom is seenin the present work, but the need lorintermediate range nucleonnuclconcorrelations (beyond that comingmerely from angular momentumcoupling in the shell model) isclearlv evident.

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Light Hypernuclei

A hypernuclei provide an op-portunity for exploring the conse-quences of depositing a strange (s)quark in a sea of nonstrange (u andd) quarks which are confined withinthe finite volume ot a nucleus. Onemight predict that in \l\c only the st|uark of the A could coexist with theI 2 u and d quarks of the 'He core inthe Is state, and that the u and dquarks are Pauli blocked from the Isshell. The consequence of such aquark shell model picture isthat AHe should be less bound thana simple AN baryon potential picturervould predict. Experimentally, s

AHedoes exhibit anomalously small binding compared to AN central forcemodel predictions. However, it ap-pears that quarks cluster into hadronsmore strongly than occurs in such anaive quark shell-model picture.Otherwise, substituting an s quark fora d quark in the unbound 5He systemcould not produce a bound \ He,while substituting an s quark fora dquark in''He to form AHe reducesthe total binding energy from 28 MeV(4He) to 10 MeV (4

AHe). The quarkgluon picture of nuclei must be morecomplex than the naive quark shellmodel.

One would like to know whether itis more economical to describe nuclei as systems of interacting baryons

"$Jr as quarkgluon composites.*"\*Clearly one does not wish to be in a

position similar to that of calculatingsuperconductivity starting fromquantum electrodynamics.) Few-body hypernuclei offer an ideal

means to investigate this question.One has a "tagged" quark or baryonwith which to work.

Improved Quark Potential

One approach to understandingthe structure of nuclei in terms ofquarks is to treat the nucleus as acollection of 3A quarks interactingvia a potential energy. In this way onetries to build nuclei from their con-stituents by calculating the wavefunction for the quarks. Once thiswave function is known, many ques-tions can be answered, such as: whatis the probability that the quarks areclustered into distinct nucleons? Thiswould replace by an actual dynamicalscheme the guesswork that is usedtoday.

A prerequisite for this program is aknowledge of the potential energyfor a system of quarks. An improvedstatic potential that is better thanthose currently in use has been de-rived from the MIT bag model La-grangian by fixing the positions ofthe quarks and solving for the shapeof the glue field and the shape of the1 !g surface. This potential consists ofa sum of two-body color Coulombterms and a many-body confiningterm, and the latter differs signifi-cantly from the popular, buttheoretically unfounded, sum of two-body potentials. The potential fromthe bag model also shows that thestring limit is not approached untilthe distance exceeds ~2 fm.

When this potential is specializedto the QQ system, it consists of aCoulomb term and a linear confining

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term, but the slope of the latter (atsmall and medium distances) is only\/2/$ of its ultimate value at largedistances (i.e., the string tension).When this potential was applied toheavy mesons such as T(bb) and\|/(cc) it gave a good tit to their.spectra. A successful prediction of themass of the F* ( cs) \\ <- also made

This potential is currently beingapplied to the simplest "nucleus"that is not a single hadron: Q2Q2)Preliminary indications are that theremaybe a true bound state of thissystem (adimeson) if the quarks aresufficiently heavy. Extensions of thisapproach to hadrons composed oflight quarks, u and d, are being considered.

CP Violation

Some aspects of the phenomenology of general SU(2)LXSU(2)R

X U( 1) electroweak models werestudied. In particular the effects ofCP-violation in the mixing of the twocharged intermediate vector bosons(WL \VR mixing) and in the quarksector on some CP-conserving ob-servables in muon decay, beta decayand double beta decay were investigated. It was found that in thepresence ot C P-violation the ratio ofthe positron longitudinal polariza-tion ir..'. Fermi beta transition and thepositron longitudinal polarization ina Gamow Teller beta transition(measured in a recent experiment)provides no limit on the righthanded boson mass, m,, even for a

given value of the WL WR mixingangle (,. Similarly, there is no boundon ^even for a given m,. It has alsobeen shown that in SU (2)L X SU (2)„X U( 1) models the rates for doublebeta decays depend on two, ratherthan one, independent complexphases.

NN—-NNn Reaction Studies

For certain exclusive kinematicssituations (resembling those for thepp—»dit+reaction), experimentshows strong enhancements in theproton momentum spectrum for verylow relative nudeon-nucleon (NN)energies in the final state. NN finalstate interactions (FSI) in thePI PROD program are now treated bymultiplying the three-body modelamplitude by a Watson-Migdal factor.(Only the Pu and P3, Ti-nucleonpartial waves in this model are inter-acting.) Up to an overall normaliza-tion factor, those exclusive differen-tial cross sections for pp—*np;t+

which show the FSI effects are verywell reproduced. Interaction in the3Sj NN partial wave turns out to bemore important than the (stronger)'So interaction, because of the specialset of selection rules that apply to thisproduction process. We have also examined various spin observahles,such as polarization asymmetries, forFSI effects. They are usually small,which is a fair representation of thepresent experimental situation.

223

RESEARCHTl"ieor,

Heretofore only one of the unitaryunified models for the coupled NN,NNnsystem has been applied to computation of two to three body reactionobservables. Recently, the isobaramplitudes of the Tjon-van Faassencoupled two-body channels modelhave been incorporated into thePIPROD code for calculatingNN—»NNTI observables. Comparisonwith previous three-body modelpredictions is now in progress.Surprisingly small differences resultfrom the Tjon-van Faassen model pmeson exchanges (e.g., changes inspin observables on the order of 0.05or less). Although differences be-tween the Tjon-van Faassen and ourmodels are often of a size to be dis-cerned experimentally (0.2 or more),there appears to he substantial modelindependence. Detailed com-parisons of the two models are cur-rently being made.

Parity Violation

A difference between the totalcross sections for positive andnegative heliciry protons scatteredfrom nuclear targets is parity violat-ing. Theory and experiment agree ona small negative value for the ratio ofthis difference to the sum, for protonenergies of a few tens of MeV. The-ories based on sums of meson exchanges predict a zero near the maximum I.AMPF energy. Beyond that,analyses extending to higherenergies which include more andmore meson exchanges produce a setof curves with increasingly positive

maximum values. A quark model calculation fitted to the positive experimental asymmetry found at 5GeV was extended to lower energies.The quark model curve matches theenvelope of the meson exchangemodel curves above 1 GeV, andagrees with the LAMPF result at H00MeV. Furthermore, the qu -'\ modelpredicts an increase in the effect byroughly a factor of 100 as the energyincreases from 5 to 500 GeV. A crucialtest of the model may be made usingthe polarized beam at Brookhaven,where a "large" value ( ~ lir1") ispredicted.

The Family Problem

The three charged leptons differonly in mass, and no other apparentproperty. Yet something dis-tinguishes them, since decays such asu.—• e+y have not been observed atall, let alone at the rate one wouldexpect from the weak interaction.This pattern is repeated for thequarks, and leads us to definefamilies of quarks and leptons, suchas e, upquark, and down-quark,where the lightest remaining of eachtype of Fermion is assigned to eachsuccessive family. The family prob-lem is that we still do not know whythere are three (or more) families,nor what distinguishes them, otherthan mass. Proposed solutions fallinto two categories: symmetrygroups, or substructures of quarksand leptons. All predict that the un-seen family changing decays, such asthe one above, or K >|i+e, do occur,however rarely. They also predict

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neutrim > mixing similar to thatknown ii 11 >ccur lor the weak interactions ot quarks. II i i s 1 cat Is to nonzeronew rim > masses, aiul to neutrino osdilations, hut the size of these ellectsis highly model dependent.

Finally, in some eases, a light ormassless scalar or pseudosealarboson is preiIicted. \\ nh couplingstrengths to I'crmions related to thescale ol family symmetry breaking. Asignal tor producing such a scalarboson, t, is u -e+l. but this can bedifficult to detect because the eleciron signal at lir = in^/i is overwhelmed by electrons from the edgeof the Michel spectrum. Instead, onecan look more easily tor theradiatively corrected process,(l—-e+Y+f. with I" earning off significant undetected momentum and zeromissing mass. The differential cross.section for this process for oneparticular type off boson couplinghas been calculated, and the XTALBOX collaboration has searched forthe reaction; preliminary data analy-sis indicates a significant lowerbound on the symmetry breakingscale. Work is continuing on the general class of processes.

Quarklei

An attempt has been made to describe nuclei direclh in lerms i >fsingle particle wavetunctions |( >rquarks m< >ving in a mean potential ina nucleus. This mean potential hasi ( msiderable local structure, similarit i that ot an egg carton. Preliminaryresults ot detailed calculations show

nudeons are little distorted in miclei, justifying the traditional mesonplus n uc I eon approach as a very goodapproximate >n. The binding energya::d matter distributions may be fairlywell described, and the modelexhibits an V.MC. effect. An immediate result ol this tiiKirk picture isthe expectation ol significant Z Amixing in hyperniielei, with specificeffects at shell closures. Progress hasbeen made on ellicient inclusion olPauli exclusion effects, in an attemptto calculate the binding energy ol4He directly in terms of quark interac-tions.

Medium Energy Probes and theInteracting Boson Model ofNuclei

The interacting boson model ofnuclei (IBM ) has been successlul indescribing the spectra and transitionrates of many types of collective nu-clei in a unified manner. This modelis an approximation to the nuclearshell model. The basic assumption isthat the low King collective states ofnuclei are composed primarily ofpairs ol protons and pairs of neutronscoupled to angular momentum zeroand two, and these coherent pairs areapproximated as bosons. The IBMalso contains a natural way for classilying nuclear states with the sameisospin but with different neutronproton symmetries.

The I.AMPP high resolution spectrometer can resolve many excitedstates ol collective nuclei. However,the extraction of nuclear structure in

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formation from the proton differen-tial cross sections tor exciting speci-fic states is complicated by the factthat coupled channel effects mightbe important at momentum transfersachievable at LAMPF, and hence thesimple DWBA cannot be used. Onthe other hand, the Glauber modelhas been successlul in describingmedium energy proton scatteringfrom nuclei, and affords a mechanismfor including such effects in a simplemanner.

The Glauber multiple scatteringseries can be approximated by an exponentiated first-order optical oper-ator. If this operator is written interms of Interacting Boson Modelcoordinates, coupled channel effectsare included to all orders. Becausethe Glauber transition operator is alinear transformation on the bosonsin the nucleus, and because the num-ber of such bosons is finite, the effectof the Glauber optical operator forscattering to any state can be calcu-lated in closed form. Analytic ex-pressions for this operator have beenderived as a function of impact pa-rameter for a spherical vibrator, a y-unstable rotor, and an axiallysym-metric prolate or oblate deformedrotor. For these types of nuclei it hasbeen shown that coupled-channel ef-fects are important at large momen-tum transfers, and fur the axinlly sym-metric rotor, at all momentum transfers.

For nuclei which are transitionalbetween these extreme limits, theprofile function must be calculatednumerically. A computer programavailable at LAMPF has been im-

plemented which calculates theproton differential cross section forexcitation to a specific nuclear statein the IBM, and which includes scat-tering to intermediate states. Thismeans that it is now possible to ex-tract meaningful nuclear structure in-formation from medium energyproton scattering to the many collec-tive states in nuclei where the IBM isapplicable. Since the IBM includesexplicitly both neutron and protondegrees of freedom, we can learnabout the different roles played byneutrons and protons in collectivemotion by analyzing both electronand proton scattering in terms of theIBM.

LAMPFII

The following T-5 staff membersmade contributions to the LAMPF IIproject: B. F. Gibson, T. Goldman, R.R. Silbar, W. R. Gibbs, P. Herczeg andS. P. Rosen.

Group T-5

Anyone wishing further informa-tion on these matters may contact T-5members J. L. Friar, W. R. Gibhs, B. F.Gibson, V (Group Leader),J. N.Ginocchio, T. Goldman, L. Heller, P.Herczeg, and R. R. Silbar. H. Hof-fman, G. Fa'ldt, and J. Speth werelong-term visitors in T-5 during 19K5.T. Otsuka, M. K. Singham, K.Maltman and G. Wenes held postdoc-toral appointments in T-5, and D.Frazer and P. Siegel are AssociatedWestern University students whoworked in T-5 during 1985.

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Group T-5 Publications

J.-P. Auger. C. Lazard, R.J. Lombard, and R. R. Silbar, "Spin Observables in theNN—NA Transition," Kucl. Pbys. A442, 62 1 ( 1985).

W. A. Beyer and L. Heller, "A SteinerTree Associated with Three Quarks",submitted tor publication.

C. R Chen. G I.. Payne,.!. L. Friar, and B. F. Gibson, "Nucleon-DeuteronDoublet Scattering Lengths with Three Nudeon Potentials", Pbys. Rev. C'doappear).

C. R Chen, G. L. Payne, J. L. Friar, and B. F. Gibson, "Convergence ofFaddeevPartial Wave Series for Triton Ground State," Pbys. Rev. C31, 2266 (1985).

C. R. Chen, G. L. Payne,J. L. Friar, and B. F. Gibson, "Faddeev Calculations ofThree-Nucleon Force Contribution to Triton Binding Energy," Pbys. Rev. Lett.55, 3" i ( 1985).

A. F. L. Dieperink and G. Wenes, "Recent Developments in the InteractingBoson Model",,Ann. Rev. Nuci. Part. Sci. 35 (1985).

J. Dubach, W. M. Kloet, and R. R. Silbar, "Nucleon-Nucleon Final StateInteractions in NN—-NNJI", Pbys. Rev. C( to appear).

J. L. Friar and W. C. Haxton, "Current Conservation and the TransverseElectric Multipole Field," Pbys. Rev. C31, 2027 (1985).

J. L. Friar, "Configuration Space Methods in the Three-Nucleon Problem",Invited lecture at the "International Symposium on Few-Body Methods",Nanning, People's Republic of China, August 4 • 10, 1985, (World Scientific,Singapore, 1986).

J. L Friar, "The Three-Nucleon Problem: Trinucleon Bound States andTrinucleon Interactions," Invited lectures at "New Vistas in ElectronuclearPhysics", Banff, Canada, August 12 - September 4, 1985 (NATO AdvancedStudy Institute), \ Plenum, 1986).

J. L. Friar, B. F. Gibson, C. R. Chen, and G. L. Payne, "Scaling Relations forTriton Ground-State Observables," Pbys. Lett. 161B, 241 (1985).

W. R. Gibbs.W. B. Kaufmann, and P. B. Siegel, "The ABC's of Pion ChargeExchange", Invited talk at the "LAMPF Workshop On Pion Double ChargeExchange,"January 10-12, 1985. (LA-1O55OC).

227

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W. R. Gihbs and D. Strottman, "High Nuclear Temperatures by AntimatterMatter Interaction," Invited talk at the "Telluride Meeting on Proton andAniiproton Nucleus Physics," March, 19KT.

"Proceedings of lladronic Probes and Nuclear Interactions", March II l-i,19HS, AU'Cuiif. I'ruc. 133, ed. by j . R. Comfort, W. R. Gibbs, and Barry G.Ritchie.

B. 1;. Gibson and R. R. Silbar, "Report on Steamboat Springs Conference,"Comments Xitcl. I'cirt. I'bys. 14 , S"" ( 19HS).

B. F. Gibson, "AI le: I ladrons or Quarks," at "International Conference onHadronic Probes and Nuclear Interact ions," AlI' Conference' !'••> feedings No.133, ed. byj. Comfort, W. Gibhs, and B. Schneider, p. 390.

J. N. Ginocchio, "A Class of Exactly Solvable Potentials, II. Three Dimensional Schrodinger Equation," .-1/;/;. ofl'bysicsl59, )6^ ( 19HS).

J. N. Ginocchio, "Low Lying Isovector Excitations in Heavy Nuclei," at"International Symposium on the Nuclear Shell Model," ed. by M. Vallieresand B. H. Wildenthal, (World Scientific, Singapore, 19H5).

J. N. Ginocchio and P. Van Lsacker, "Determination of the Neutron and ProtonEffective Charges in the Quadrupole Operator of Nuclear Collective Models,"I'bys. Rev. C'( to appear).

J. N. Ginocchio, T. Otsuka, R. Amado, and D. Sparrow, "Medium EnergyProbes and the Interacting Boson Model of Nuclei," I'bys. Rev. (7 do appear).

T. Goldman and M. M. Nieto, "Gravitational Properties of Antimatter",Proceedings of the 3rd LEAR Workshop (Tignes Savoie, France,Jan. 19K5),"Physics with Antiprotons at LEAR in the ACOL Era," ed. by V. Gastaldi, R.Klapisch.J. M. Richard, and J. Tran Thanh Van ( Editions Fronlieres, l9H5),p.639.

T. Goldman and M. M. Nieto, editors, "Proceedings of the Santa Fe Meeting",Division of Particles and F'ields, American Physical Society, 19H4 (WorldScientific, Singapore, 19HS ).

T. Goldman, "Quark Structure of Nuclei", at "Hadronic Probes and ?Interactions", (Tempe, Arizona, March 19HS), All'Conf. I'roc. 133, eComfon, W. R. Gibbs.and B. G. Ritchie, p. 203.

Nuclear133,ed.byJ.R.

T. Goldman, "Do Nucieons Dissolve?", Proceedings of the Santa BarbaraWorkshop on Nuclear Chromodynamics, ( UC-Santa Barbara, August I9HS ).

12H

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i i itiOl y

L. Heller and |. A.Tjon, On Bound States of Heavy Q"Q" Systems", I'bys. Rer.i

L. Heller and j . A . Tjon, "! leasy Dimesons", Proceedings of the Santa FeMeeting nl'ihe iJivisii>u o!' Particles and Fields, American Physical Society,I9,s-i. ed. by T. Goldman and M. M. Nieto, (World Scientific, Singapore, 19K5 )

L. Heller. A Better Potential for Quarks", at "Hadronic Probes and NuclearInteract11 ins", i 'l'empe, Arizona, March 1985 ), All'(.'on/. I'roc. 133, ed. byJ R.Comlurt. W K. Cribbs, and IV G. Rue hie.

1.. Heller. The Potential Energy lor Quarks," to be published in the Proceedings of the Workshop on Nuclear Chromodynamics: Quarks and Gluons inParticles and Nuclei, the Institute for Theoretical Physics, University ofCalifornia. Santa Barbara, CA, August 12-23. 1985.

P Here/eg, "Some F.ffects of CP Violation in Sl'( 2 )LX SL'(2 )„ X l'( 1 )Electroweak Models", invited talk at the Third Telemark Miniconference onNeutrini > Mass and Low Fnergy Weak Interactions, October 2^-2"", 19K~t,Telemark Lodge, Wisconsin, LA I'R 85 l.-Vn, Proceedings, (World Scientific,Singapore. I98(O.

P. Here/eg, "On Miiuii Decay in Left Right Symmetric Electroweak Models."LA IK 85 2~(>1, submitted to Nuclear Physics B.

C. L. Hollas, K. H. McNaughton, P. J. Riley, Shen-\X'u Xu, B. E. Bonner, O. B.van Dyck.J. Met",ill, M. W. McNaughton, J. C. Peng.J. Dubach, W. M. Kloet,and R. R. Silhar, "Wolfenstein Polarization Obsen rables for the Reactionpp-*p+n at HOO MeV". I'bys. Rev. Lett. 55, 29 ( 19«T>.

C Milner. M. Barlett, G. W. Hoffmann, S. Bart, K. E. Chrien, P. Pile, P. D.Barnes. (.,. B. Franklin. R. Grace, H. S. Plendl.J. F. Amann.T.S. Bhatia.T.Kozlouski.J. C. Peng, R. R. Silbar. H. A. Thiessen, C. Glashausser.J. A. McGill,R llac keuburg. E. \ . 1 lungerford. and R. L. Stearns, "Observation of A-Hvperuudei inthe IJC(7t+, K+) 1^: Reaction". I'bys. Her. Lett. 54, 12.^ ( 19HS).

T. ( >lsuka and J. N. Ginocchio. "Low Lying Isovector Collective States and theInteracting Boson Model." I'bys. h'er. Lett. 5 4 , " " " ( 1985).

T. ( Hsuka and j . N. Ginocchio, "Renormalization of g boson Effects in theInteracting Boson Hamiltonian," I'bys. Rev. Lett. 55, 2"6 ( 1 9 ^ ) .

P B. siegel, W. B. Kaufmann, and W. R. Gibbs, "K + asa Probe of PartialDeconfinemeni in Nuclei", I'bys. Rev. C31, 21H4 ( 19H5).

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P. B. Siegel, W. B. Kaufmann, and W. R. Gibbs, "K+ as a Probe of PartialDeconfinement in Nuclei," at "Hadronic Probes and Nuclear Interactions",Tempe, Arizona, March, lyK5).

P. B. Siegel and NX'. R. Gibbs, "Pion Nucleon Charge Exchange and Scatteringat Low Energies", (Submitted to Pbys. Rcr. C.) (LA UR-KS 391S.)

E. L. Tomusiak, M. KinuiraJ. L. Friar, B. !•'. Gibson, G. L. Payne, and) . Dubach,"Trinudeon Magnetic Moments", I'bvs. Rev. C'(toappear).

S. V. Van der Weil, N. Blasi, M. N. Harakeh, G. Wenes, A. D. Bacher, G. 1'.Emers-, ('.. \ \ \ Glover, W. I1. Jones, 11. J. Karwowski, H. Nana, C. Oliner, P. denHeijer, C. W. dejager, H. de Vires, J. Ryckebusch, M. Waroquier, "High Spinlp-lh Configurations in 1HlSnand their Fragmentation as Seen in the Reactionl l bSn(p,p ' ) , U 6Sn(e,e), " ' In( 3He,d) and " ' ' (a . t) ." (Phys. Lett., to be pub-lished).

G.Wenes, A. E. L. Dieperink and N. Yoshinaga, "Algebraic Treatment ofMulti step Excitation Processes in Collective Nuclei (II) ElectromagneticExcitation of Collective Nuclear States", M/c/. I'bys. A443, 472 (19H"S).

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MP-DIVISiON PUBLICATIONS

Publications Nuclear and Particle Physics Research

L. Adiels, G. Backenstoss, I. Bergstrom, S. Carius, S. Charalambous, M.Cooper, C. l-'indeisen, D. Hadjifotiadou, A. Kerek, K. Papastelanou, P.I 'avlopoulosJ. Repond, L. Tauscher, D. T rosier, M. C. S. Williams, and K.Zioutas, "Investigations of Baryonium and Other Rare />/> Annihilation ModesUsing High -Resolution n" Spectrometers (PS 1H2)," Institute ufl'bysics Con-ference Series73, 297-3<>4 ( 19K4).

I.. Adiels, G. Backenstoss, I. Bergstrom, S. Caruis, S. Charalambous, M. D.Cooper, C. Findeisen, D. 1 ladjifotiadou, A. Kerek, K. Papastefanou, P.Pavlopoulos,]. Repond, L. Tauscher, D. Troster, M. C. S. Williams, and K.Zioutas, "A 7t" and r| Spectrometer of Lead Glass and BGO for Momenta up to1 GeV/c," CERN report EP/SS- l4(> (submitted to Nuclear Instruments &Methods).

R. C. Allen, V. Bharadwaj, G. A. Brooks, H. H. Chen, P. J. Doe, R. Hausammann, W. P. Lee, H. J. Mahler, M. H. Potter, A. M. Rushton, K. C. Wang, T. J.Bowles, R. L. Bur man, R. D. Carlini, D. R. F. CochranJ . S. Frank, E. Piasetzky,V. D. Sandberg, D. A. Krakauer, and R. L. Talaga, "First Observation and Cross-Section Measurement ot vt, + <~ —• v,, + e~," Physical Review Letters 55, 2401(19HS).

H. W. Baer, "Pion Single- and Double-Charge-Exchange Scattering: Genera!Features of Analog and Double-Analog Transitions," "Proceedings of theLAMPF Workshop on Pion Double Charge Exchange," Los Alamos NationalLaboratory report LA- 10550-C (September 19HT),pp. 4vH9.

H. W. Baer, "Pion-Nucleus Double Charge Exchange: The Modern Era" (to bepublished in Comments on Nuclear and Particle Physics), Los AlamosNational Laboratory document LA-LIR-HS 1M)H-R ( 19HS).

G. S. Blanpied, B. G. Ritchie, M. L. Barletl, G. W. Hoffmann, J. A. McGill, M. A.Franey, and M. Ga/./aly, "Elastic Scattering of 0.H Ge\ ' Protons from the NonZero-Spin Nuclei "C and "N." Physical Review f.'32, 21S2 ( 19«5).

R. D. Bol tonJ . D. Bowman, R. Carlini, M. D. Cooper, M. Duong-Van,J. S.Frank, A. L. Hallin, P. Heusi, C. M. Hoffman, F. G. Mariam, H. S. Mai is, R. E.Mischke, D. E. Nagle, V. D. Sandberg, G. II. Sanders, 1.'. Sennhauser, R. L.Talaga, R. Werheck, R. A. Williams, S. L. Wilson, E. B. Hughes, R. Hofstadtcr,D. Grosnick, S. C. Wright, G. E. Hogan, and V. L. Highland, "Search for theMuon-Number-Nonconserving Decay u. —• e+c+e~," Physical Review Letters53, H I S ( 19«4).

RESEARCH1 '..locations

R. D. Bolton.J. D. Bowman, M. D. Cooper,J. S. Frank, A. L. Hallin, P. Heusi.C.M, Hoffman, G E. Hogan, I-'. G. Mariam, 11. S. Mati.s, K. E. Mischke, D. E. Nagle,L. E Piilonen, V. IX Satulberg, G, II. Sanders, LI. Sennhau.ser, R. Werbeck, R. A.Williams, S. L Wilson, R. llolstadler, li. B. I lughes, M. W. Ritter, D. Grosnick,S. C Wright, \'. L. Highland, and J. V.cDonough, "Search tor the Decayjif ••— I-^Y" (submitted to Physical Review Letters).

R IX Bolton, M IX Cooper, I. S. Frank, \r. E. Hart, II. S Mati.s, R. E. Mischke, V.IX vmdberg, I 1'. Sandoval, and I'. Sennhauser, "Performance ot the Cylindricial Drift Chamber lor the t instal Box at LAMPF," Nuclear Instruments &Methiuls A241, Si ( I'JHS ).

R I. Boudrie,J. R. Shepard, and C. N'. Cheung, Lids., "Proceedings ol'theLAM PI' Workshop on Dirac Approaches to Nuclear Physics," Los AlamosNational Laboratory report LA \i)\W C (May IWi t .

J. D Bowman, isosector Resonances in Pion Charge Exchange," Proceedings ot the Symposium on Nuclear Structure, Niels liohr Centennial Con-ferences, Ricardo Broglia Giidrunhageniann and Bent llerskind, lids. (NorthHolland, Amsterdam, 1WS), p. s.ty.

K A. Brown, R.J. Bruni, P. R. Cameron, IX G. Crahh, R. L. Cummings, I-'. Z.Khian, A. I). Krisch, A. M. T. Lin, R. S. Raymond, T. Roser, K. M. Terwilliger, G.T LXanby, L. G. Ratner, DC. Peaslee.J. R. O'Fallen.J. B. Roberts, T. S. Bhatia,L. C. Northclifte, and M. Simonius, "Spin-Spin Effects in/?/;—* /)/) atib.S GeYA." Physical Rericw D 3 1 , 301" ( I98S).

R. L. Burman, "Neutrino Electron Scattering," Physics Today S-50 (January19H(>).

P. R. Cameron, D. G. Crabb, G. E. DeMuth, F. 7. Khiari, A. D. Krisch. A. M. T.Lin. R. S. Raymond, T. Roser, K. M. Terwilliger, K. A. Brown, G. T. Danby, L. G.Ratner,J. R. OTallen, D.C. Peaslee.J. B. Roberts, T. S. Bhatia, and M.simonius, "Measurement of the Analyzing Power for/' + />/> + /; at />]_ = 6.Sl G c \ / c i J . " Physical Review 1) 32, ;Mri) ( 19HS).

K Carlini. C l-'rieelrichs, and H. A. Thiessen, "A Transversely Biased F'erriteTuned Cavity lor the SSC Booster." Proceedings of the SuperconductingSuper Collider Injector Workshop. Berkeley, California, Novemher 1H-20,19HS

R. Carlini, V. Sandberg, and H. A. Thiessen, "Idea foi a Variable ImpedanceBeam Pipe," Proceedings of the Superconducting Super Collider ImpedanceWorkshop, Berkeley, California, June 26-2~\ 19H5.

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J.Ch;ilmers, W. R. Ditzler, T. Shima, H. Shimizu, H. Spinka, R. Stanek, D.Underwood, R. Wagner, A. Yokosawa, J. E. Simmons, G. Burleson, C.Fontenla, T. S. Bhatia, G. Glass, and L. C. Northcliffe, "Measurements of Ku

and KNN in p?/ — nppiu 500, 650, and 800 MeV," Physical Letters 153B, 235(19HS).

E. P. Colton, "Acceleration Simulation in the LAMPF II Booster," IHhiiTransactions on Nuaear Science NS-32(5), 2567-2569 ( 1985).

E. P. Colton, "Longitudinal Tune Control in Synchrotrons," IEEE Transac-tions on Nuclear Science NS-32(5), 2570-25^2 (1985).

E. P. Colton, "Slow Extraction at LAMPF II,"IEEE Transactions on NuclearScience NS-32(5), 2^4 1-2443 (1985).

E. P. Colton, "Slow Extraction at the SSC," IEEE Transactions on NuclearScience NS-32(5), 2442-2443 (1985).

E. P. Colton, "The rf Program for LAMPE II," IEEE Transactions on NuclearScience NS-32(5), 25~\3 2575 ( 1985).

E. P. Colton and H. A. Thiessen, "Some Thoughts on H~ Injection into SSC,"Proceedings of the Superconducting Super Collider Injector Workshop,Berkeley, California, November 18-20, 1985.

E. P. Colton and T. F. Wang, "SSC Kicker Impedances," Proceedings of theSuperconducting Super Collider Injector Workshop, Berkeley, California,November 18-20, 1985.

M. D. Cooper, "Muon Number Violating Rare Decays,'.' Proceedings of theInternational Eiirophysics Conference on High-Energy Physics, Bari, Italy,July 18-24, 1985.

K. S. Dhuga, G. R. Burleson, J. A. Faucett, R. L. Boudrie.W. B. Cottingame, S. J.Greene, C. L. Morris, N. Tanaka, Z. F. Wang, S. Nanda, D. Dehnhard, J. D.Zumbro, S. Mordechai, C. F. Moore, and D. J. Ernst, "Large-Angle ElasticScatteringof 7i+and 7t~ from 16O at 14 MeV" (submitted to Physical Review),Los Alamos National Laboratory document LA L'R-85-2798 (1985).

J. A. Faucett, B. E. Wood, D. K. McDaniels, P. A. M. Gram, M. E. Hamm, M. A.Oothoudt, C. A. Goulding, L. W. Swenson, K. S. Krane, A. W. Stetz, H. S.Plendl, J. Norton, H. Funsten, and D.Joyce, "Kinematically Complete Meas-urement of the (iPj&p) Reaction on 12C at 220 MeV," Physical Review (7 30,1622(1984).

RESEARCH

Publications

R W. Ivigerson, M. L. Barlett, G. W. Hoffmann,J. A. Marshall, E. C. Milner, G.Pauletta, L. Ray, J. F. Amann, K. W. Jones,J . B. McClelland, M. Ga/zaly, and G.J. lgo, The Spin Rotation Parameter Q for 800 MeV l'roton Elastic Scatteringfrom '"O, '"Ca, and J"RPh," Physical Review CH, 1 ( 1986), Los AlamosNational Lihoraiory document LA -UK 85 24H(> ( 1985).

R \\ Fergerson, "The Spin Rotation Parameter Q for Elastic Scattering of 800-Million Electron Volt Protons from Oxygen Id, Calcium -t(), and Lead-208,"Thesis, Los Alamos National Laboratory report LA I O S S I T" (October 1985).

1> H [•'it/gerald. It. W Uaer.J. P. Bowman, F. Irom, N. S. P. King, M.J. Leitch,E Piasetzky. \V. J. Briscoe, M. F. Sadler, K.J. Smith, and j . N. Knudson,"Forward Angle Cross Sections for l \on Nucleon Charge Exchange Between100 and ISO MeV/c" (submitted to Physical Review C).

J S Frank, T. J. Bowles, R. L. Burman, R. D. Carlini, D. R. F. Cochran, E.Piasetzky, V. D. Sandberg, R. C. Allen, V. Bharadwaz, H. H. Chen, P. J. Doe, R.Hausammann, H.J, Mahler, K. C.Wang, D. A. Krakauer, and R.C.Talaga,"Observation ol v,.-i' Elastic Scattering," Proceedings of the Twenty-SecondInternational Conference on High-Energy Physics { Leipzig, DDR, 19H-1),Vol I, p. J3I.

F. C. Gaille, V. L. Highland, L. B. Auerbach, W. K. McFarlane, G. E. Hogan, C.M. Hoffman, R. j Macek, R. E. Morgado, J. C. Pratt, and R. D. Werbeck, "PreciseMeasurement of the Pion Charge-Exchange Forward Differential Cross Sec-tion at 522 MeV./c," Physical Review D 30, 2408 (1984).

S. Gilad, VC'.J. Burger, G. W. Dodson, S. Hoibraten, L. D. Pham, R P. Redwine,E. Piasetzky, H. W. Baer,J. D. Bowman, F. H. Cverna, M.J. Leitch, U.Sennhauser, T. S. Bawer, C. H. Q. Ingram, G. S. Kyle, D. Ashery, S. A. Wood,and Z. Fraenkel, "Measurement of the lf'O(7i+\n°p) Reaction" (submitted toPhysical Review (.').

R Oilman, II T Fortune,J. D Zumhro, P. A. Seidl, C. F. Moore, C. L. Morris,J.A. Faucett, G. R. Burleson, S. Mordechai, and K. S. Dhuga, "Angular Distribu-tions for "C"hMg(7r+,7t")" (submitted to Physical Review C), Los NationalLaboratory document LA LIR 85•2"'Sl) ( 1985).

R. Oilman, H. T. Fortune,). D. Zumbro, C. M. Laymon, G. R. Burleson,J. A.Faucett, \X\ B. Cottingame, C. L. Morris, P. A. Seidl, C. F. Moore, L. C. Bland, R.R. Kiziah, S. Mordechai, and K. S. Dhuga, "Mass Dependence of Pion DoubleCharge Exchange" (submitted to Nuclear Physics), Los Alamos NationalLaboratory document LA UR 85-3218 ( 1985).

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R. Oilman, H. T. Fortune, M. B.Johnson, E. R. Siciliano, H. Toki, and A.w 'irzba, "Nonanalog Pion Double Charge Exchange Through /1,,-NuclfimInteraction," Physical Review C 32, 3-iS) ( 19KT).

R. Oilman, "Systematic* of Pion Double Charge Exchange," Thesis, LosAlamos National Laboratory document LA-loSii -T (October 19HS).

G. Glass, T. S. Bhatia.J. C. Hiebert, R. A. Kenefick, S. Nalh, L. C. Northdiffe, W.B. Tippens, D. B. Barlow, A. Saha, K. K. Seth.J. O.J. BoissevainJ.J.Jarmer,J.E. Simmons. R. H. Jeppesen, and G. E. Tripard, "Measurements ol SpinCorrelation Parameters . l u and <-lVi for/>/.) — n<l Between SOD and KOi) MeV,"Physical Review C 3J, ^ 8 ( IWS ).

R. W. Harp-r, V. Yuan, 11. l 'rauenlelder.J. D. Bowman, R. Cadini, R. E.Mischke, D. E. Nagle, R. L. Talaga, and A. B. McDonald, "Parity Nonconserva-tion in Proton Water Scattering at I.T GeV/f," Physical Review D 31 , 1 l^l(1985).

C. J. Hur\"ey, H. W. Baer, J. A. Johnstone, C. L. Morris, S. J. Seestrom Morris, D.Dehnhard, D. B. Holtkamp, and S. J. Greene, "Elastic K+ and n~ Scattering on14Cat Kvi MeV." Physical Review C (in press).

R. S. Hicks, R. A. Lindgren, M. A. Plum, G. A. P-terson, H. Crannell, D. 1.Sober, H. A. Thiessen, and D.J. Mi'lener, ".1/4 Excitations in MC" (submittedto Physical Review).

C. M. Hoffman, R. D. Bolton, M. D. Cooper, J. S. Frank, A. L. Hallin, P. lleusi,G. E. Hogan, L. E. Piilonen, E. G. Mariam, H. S. Matis, R. E. Mischke, I). E.Nagle, V. D. Sandberg, G. H. Sanders, U. Sennhauser, R. Werbeck, R. A.Williams, S. L. Wilson, R. Holstadter, E. B. Hughes, M. Ritter, D. Grosnick, S.C. Wright, V. L. Highland, and J. McDonough, "Search for Rare MmmNumber -Non Conserving Decays of the Ji+," in the Proceedings ol the 19H5International Symposium on Lepton and Photon Interactions at High Energy,Kyoto,Japan, August 19 2-1, 19H5.

G. F. Hogan, R. D. Bolton.J. D. Bowman, R. Carlini, M. D. Cooper, M. Duong-Van.J. S. Frank. A. L. llallin, P. Heuse, C. M. Hoffman, F. G. Mariam, H. S.Matis, R. E. Mischke, D. F. N'agle, V. D. Sandberg, G. H. Sanders, li. Sennhauser, R. L. Talaga, R. Werbeck, R. A. Williams, S. L. Wilson. E. B. Hughes, R.Hofstadter, Cj. Grosnick, S. C. Wright, and V. L. I lighland. "A Progress Reporton Recent Rare Muon Decay E\j>emnent.s at the Los Alamos Meson PhysicsFacility," Xuclear 1'bysics A434, i^Sc ( 19SS ).

236

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Publications

D. B. Holtkamp, S.J. SeestronvMorris, D. Dehnhard, H. W. Baer, C. L. Morris,S.J. Greene, C.J. Harvey, D. Kurath.andJ. A. Carr, "Pion Scattering to 4" Statesin UC," Physical Review C 31,9=57 (1985).

D J. Horen, F. E. Bertrand, E. E. Gross, T. P. Sjoreen, D. K. McDanielsJ. R.Tinsley.J. Lisantti, L. W. Swenson.J. B. McClelland, T. A. Carey, S.J. SeestromMorris, and K.Jones, "Cross Sections and Analyzing Powers for QuenchedSpin Excitations in '"'aCa at Ep = 33-t MeV," Physical Review C 31, 2049(1985).

F. lrom, 11. W. BaerJ. D. Bowman, M. D. Cooper, E. Piasetzky, U. Sennhauser,H.J. Ziock, M.J. Leitch, A. Erell, M. A. Moinester, andj. R. Comfort, "PionSingle Charge Exchange on "Li at Low Energies," Physical Review (7 31,1464(1985).

F. Irom, H. W. Baer, J. D. Bowman, M. D. Cooper, E. Piasetzky, M.j. Leitch, B.J. Dropesky, andj. N. Knudson, "The Energy and Mass Dependence of Low-Energy Pion Single Charge Exchange to the Isobaric Analog State," PhysicalReview Letters 55, 1862 ( 1985).

M. VC. Johnson. E. B. Shera. M. V. Hoehn, R. A. Naumann.J. D. Zumbro, and C.E. Bemis, Jr., "-""Am and ;ilAm Charge Distributions from Muonic X RaySpectroscopy and the Quadrupole Moment of the 24"Am Fission Isomer,"Physical Review Letters 161B, ^5 (1985).

K. W. Jones, C. Glashausser, R. de Swiniarski, S. Nanda, T. A. Carey, W.Cornelius, J. M. Mos.s.J. B. McClelland, J. R. Comfort, J.-L Escudie, M. Gazzaly,N. Hintz, G. Igo, M. Haji Saeid, and C. A. Whitten, "Energy Dependence ofDeformation Parameters in the l2C(p!//)12C Reaction," Physical Review C 33,17 (1986), Los Alamos National Laboratory document LA-UR-85-2483 (1985).

G.J. Krausse, "A U) MHz High-Voltage Modulatorwith Pulse Width andRepetition Rate Agility." submitted to the 5th IEEE Pulsed Power Conference.Arlington, Virginia.

M.J. Leitch. H. W. Baer,J. D. Bowman, M. D. Cooper, E. Piasetzky, U.Sennhauser, H.J. Ziock, F. !rom,J. R. Comfort, P. B. Siegel, and M. A.Moinester. "Pion Single Charge Exchange Angular Distribution at7; = 48 MeV.' Physical Review C 33, 278 (1986).

M.J. Leitch, E. Piasetzky, H. W. Baer.J. D. Bowman, R. Burman, B.J Dropesky,P. A. M. Gram, F. Irom, D. Roberts, G. A. Rebka,Jr.,J. N. Knudson, J. R.Comfort, V. A. Pinnick, D. H. Wright, and S. A. Wood, "Double AnalogTransition I4C(K+,7C")'4O at 50 MeW," Physical Review Letters 54,1482 (1985),

237

RESEARCH

D. H. Lobb, "A 0.8 GeV/c Kaon Channel for LAMP!" I!," Los Alamos NationalLaboratory report LA inSyy MS ( 19KS).

I). W. MacAnhui, "Device to Generate Intensity Modulation in a PulsedPanicle Beam" (submitted to Nuclear Instruments & Methods A ).

D. \V. MacAnhur, "Special Relativity: Understanding I'xperimental Tests"(submitted to Physical Review A ).

D W. MacArthur, K. B. IHitierfield, IX A. Clark,|. B. Donahue, P. A. M. Gram,11. (1. Bryant, C.I.I larvey, and W. W. Smiih, "Test o ld ie Special RekitivisiicDoppler Formula at [i = n.K-i." I'bysical Review Letters 56,1X1 ( I'JHSl.

D.\X\ MacArthur, K. B. Butierl'ield, D. A. Clark,J. B. Donahue, P. A. M. Gram,II. C. Bryant, C.J. Harvey. \X'. W. Smith, and G. Comtet, "Hnergy Measurementof the Lowest '/••„ Feshhach Resonance in \\~," Physical R"view A 32, 1921(19HS) .

D. W. MacArthur, R. Lr. Mischke, and J. P. Sandoval, "Fast Integrating Multiwire Beam Profile Monitor with Digital Readout" (submitted to NuclearInstruments & Methods A ).

RobertJ. Macek, "LA.MPI; II Cajiabilities from an Hxperimenter's Viewpoint, "invited talk at the Workshop on Nuclear and Particle Physics at IntermediateEnergies with Madrons, International Center for Theoretical Physics, Trieste,Italy, April 1 3, 19H=S (to be published in the proceedings).

RobertJ. Macek, "Review of Proposed Kaon Factors' Facilities," All'Con-

ference Series 133, 3-i6 3^> ( 19HT ).

C.J. Martoff.J. A. Bistirlich, C. W. Clawson, K. M. Crowe, M. Koike,J. P. Miller,S. S. Rosenblum, VC'. A. Zajc, H. V('. Baer, A. II. Wapstra, G. Strassner, and P.fruol, "Spin Flip Transitions in I1C and '''F Probed with the (7C~,y) Reaction,"I ' h y s i c a l R e v i e w C 2 1 , I d i l ( 1 9 K 3 ) .

NX' K. McFarlane, L. B. Auerbach, F. C. Gaille, V. L. Highland, F.. Jastr/.embski,R.J. .Macek, F. H. Cverna, C. M. Hoffman, G. K. Hogan, R. \L. Morgado.J. C.Pratt, and R. D. Werbeck, "Measurement ofthe Rate for Pion Beta Decay,"Physical Review D 32, S-r ( 19K5 ).

C. Milner, M. Barlett, G. W. Hoffmann, S. Bart, R. E. Chrien, P. Pile, P. D.Barnes, G. B. Franklin, R. Grace, H. S. Plendl.J. F. Amann, T. S. Bhatia, T.Kozlowkski.J. C. Peng, R. R. Silbar, H. A. Thiessen, C. Glashausser.J. A.McGill, R. Hackenburg, E. V. Hungerford, and R. L. Stearns, "Observation ofA Hypernuclei in the Reaction 11C(K\K+)\2C," Physical Review Letters 54,1237(1985).

238

RESEARCH

Publications

R. E. Mischke, Parity Nonconservntion in Light Hadronic Systems," Proceed-ings of the Panicles and Nuclei Tenth International Conference, Heidelberg,Germany,July .-Mi August 3, 19K-1, pp. =>05c 5l-ic.

C. S. Mishra. H. G. Ritchie. R. S. Moore, M. lilecher, K. Golow, K. L. Burnuin, M.V. Hynes, F.. Piaset/ky. N. s. Clhant. P. G. Roos, T. Sjorecn, I'. Li. Obenshain,and E. Li. tiros-.. Isospin Effect in jr.* ''C Elastic Scattering at SO MeV,"Physical Rvrii'ii f ' 3 2 , W=- ( 1WS).

S. Mordechai. I'. A Seidl. C i: Moore, L ('.. Bland, K. tiilman, K. S. Dhuga, 11.T Fortune. (! 1- Morris, and S J. Greene. "Systematics of Continuum PionDouble Charge Exchange on '/'= o Nuclei,' Physical Rcrivir (. '32,999( 198S ), Los Alamos National Laboratory document LA UR K5 I T H I IW>).

D. E. Nagle. R. D. Bolton, R. L. Burman, K. B. Buttert'ield, R. D. Carlini.J. S.Frank, W. Johnson, \'. D. Sandberg, G. B. Yodh, G. A. Goodman, R. L. Talaga,B. Dingus, X. Chang. R. \X\ Ellsworth, J. Linsley, H. Chen, R. C. Allen, P. J.Doe, and V. T. Lee. "The 'Cygnus' Experiment at LAMPF," Proceedings of theWorkshop on a Gamma Ray Air Shower Detector, San Diego, California,August W, I 9 K T

S. Nanda, "Spin Excitations in'"lCa and 9"Zr with 319 MeV Protons," Thesis,Los Alamos National Labi >ratory report LA-L03^«T (May 198S).

H. W. Baerand M.J. Leitch, Eds.."Proceedings of the LAMPF Workshop onPion Double Charge Exchange," Los Alamos National Laboratory reportLA-1055O-C (September 19KS).

R. S. Raymond, K. A. Brown, R. J. Bruni, P. R. Cameron, D. G. Crabb, R. L.Cummins, F. Z. Khiari, A. D. Krisch, A. M. T. Lin, K. M. Terwilliger, G. T.Danby.Y. Y. Lee, L. G. Ratner.J. R. O'Fallen, D. C. Peaslee.T. S. Bhatia,G.Glass, and L. C. Northcliffe, "Analyzing Power Measurements forpp ElasticScatteringat High P[" (submitted to Physical Review Letters).

I. B. Rees, J. M. Moss, T. A. Carey, K. W. Jones,J. B. McClelland, N. Tanaka, A.D. Bacher, and E. Esbensen, "Continuum Polarization Transfer in 500 MeVProton Scattering and Pionic Collectivity in Nuclei" (submitted to PhysicalReview), Los Alamos National Laboratory document LA-UR-86 35 ( 1986).

R. Rieder, P. D. Barnes, B. Bassalleck, R. A. Eisenstein, G. Franklin, R. Grace,C. Maher, P. Pile, J. Szymanski, W. R. 'JCharton, F. Takeutchi, J. F. Amann, S. A.Dytman, and K. G. R. Doss, "Triple-Differential Cross Sections of the (n+,pp)Reaction on Lithium isotopes" (submitted to Physical Review C), Los AlamosNational Laboratory document LA UR 85-586 (1985).

239

RESEARCHpuDiicanons

V. D. Sandberg, L. S. Bayliss, M. F. Dugan.J .S. Frank,! . Gordon, G. W. H;in,C.M. Hoffman, G. E. Hogan, 11. S. Minis, G. II. Sanders, and II. P. von Gunten, ' AFast Analog Mean-Timer," Nuclear Instruments & Methods A234, S12 S16(1985).

P. A. Seidl, C. F. Moore, S. Mordechai, R. Gilman, K. S. Dhuga, 11. T. Fortune, ].D. Zumbro, C. L. Morris, J. A. Faucett, and G. R. Burleson, "The EnergyDependence of 1BO(7r+,7t")IHNe (g.s.) ," Physics Letters 154B, i 55 ( 1985), LosAlamos National Laboratory document LA-UR-H-i-3373 ( 19H-i).

P. A. Seidl, "The Measurement of Pion Double Charge Exchange onCarbon-13, Carbon- l-i, Magnesium 2(>, and Iron-56," Thesis, Los AlamosNational Laboratory report LA-10338 T (February 1985).

E. R. Siciliano, M. D. Cooper, M. B.Johnson, and M.J. Leitch, "Effect ofNuclear Correlations on Low-Energy Pion Charge-Exchange Scattering" (submined to Physical Review C), Los Alamos National Laboratory document LAUR-86 -K)6(1986).

W. W. Smith, C. Harvey, J. E. Stewart, H. C. Bryant, K. B Butterfield, D A.Clark, J. B. Donahue, P. A. M. Gram, D. MacArthur, G. Comtet, and T.Bergeman, "Simple Atomic Systems in Strong External Fields," in AtomicExcitation and Recombination in External Fields, M. H. Nayfeh and C. W.Clark, Eds. (Gordon and Breach, New York, 1985).

W. R. Smythe, T. G. Brophy, R. D. Carlini, C. C. Friedrichs, D. L. Grisham, G.Spalek, and L. C. Wilkerson, "rf Cavities with Transversely Biased FerriteTuning," IEEE Transactions on Nuclear Science NS-32(5), 29^1 (1985).

D. A. Sparrow, J. Piekarewicz, E. Rost, J. R. Shepard, J. A. McNeil, T. A. Carey,andj. B. McClelland, "Relativistic Impulse Approximation, Nuclear Currents,and the Spin-Difference Function," Physical Review Letters 54, 2207 (1085).

H. A. Thiessen, "A Review of Kaon Factory Proposals,"//:'/;'/:' Transactions on

Nuclear Science NS-32(5), 16011606 ( 1985).

C. Tschalar, "Multiple Scattering: A General Formalism for Small Angles," LosAlamos National Laboratory report LA-10620 ( 1985).

J. L. Ullman, P. W. F. Alons.J.J. Kraushaar.J. II. Mitchell, R. J. Peterson, R. A.RistinenJ. N. Knudson.J. R. Comfort, H. W. Baer,J. D. Bowman, D. H.Fitzgerald, F. Irom, M. J. Leitch, and E. Piasetzky, "Pion Single ChargeExchange on HC from 35 to 295 MeV" (submitted to Physical Review C).

240

RESEARCH

PuDlications

S. L. Wilson, "A Search for the Neutrinoless Decay \i+ —- e+y," Thesis, LosAlamos National Laboratory report LA 10471 T (1985).

V. Yuan and J. D. Bowman, "Study of LAMPF H~ Beam Position Motion and aPredictive Algorithm tor Noise Reduction," IEEE Transactions on NuclearSciencc NS-32(5), 19""9 1981 ( 1985).

Applications-Oriented Research

C. Boekema, K. C. B. Chan, R. L. Lichti, V. A. M. Brabers, A. B. Denison, D. W.Cooke, R. H. Heffner, R. L. Hutson.andM. E. Schillaci, "AnSRStudyofValence Fluctuation in Fe3O.,," Proceedings of the International Conferenceon Magnetism (North Holland, Amsterdam, 1985) (tc be published in theJournal of Magnetism and Magnetic Materials).

C. Boekema, R. L. Lichti, V. A. M. Brabers, A. B. Denison, D. W. Cooke, R. H.Heffner, R. L. Hutson, M. Leon, and M. E. Schillaci, "Magnetic Interactions,Bonding, and Motion of Positive Muons in Magnetite," Physical Review B 31,1223 ( 1985).

C. Boekema, R. L. Lichti, K. C. B. Chan, V. A. M. Brabers, A. B. Denison, D. W.Cooke, R. H. Heffner, R. L. Hutson, and M. E. Schillaci, "ExperimentalEvidence for a MottWigner Glass Phase of Magnetite Above the VerweyTemperature," Physical Review B 33, 210 (1986).

R. D. Brown, "Power Deposition Measurements at the LAMPF NeutronRadiation Effects Facility," Los Alamos National Laboratory report LA-10448-MS(May 1985).

R. D. Brown,}. R. Cost, andj. T. Stanley, "Irradiation-Induced Decay ofMagnetic Permeability of Metglas 2AO5S-3 and Mumetal," Journal of NuclearMaterials 131, 3 7 ( 1985).

K. C. B. Chan, C. Boekema, R. L. Lichti, D. W. Cooke, M. E. Schillaci, and A. B.Denison, "Magnetic Interaction Localization and Motion of Positive Muons inV,O," (to be published in the Journal of Magnetism and MagneticMaterials).

J. S. Cohen and M. Leon, "New Mechanism for Resonant dtp. Formation andEpithermal Effects in Muon-Catalyzed Fusion," Physical Review Letters 55, 52(1985).

241

RESEARCH

J. S. C o h e n a n d M. Leon, "Targe t D e p e n d e n c e o f t h e effective StickingProbabi l i ty in iMuon Catalyzed ill l-usi. <n," Physical Review A 3 3 , 1 i 3 "( 1986).

D.W. Cooke.J. K. Hotter, M. Mae/, \X\ A. Sieyeri.and R 11 I Miner, "ADilution Refrigerator for Mi..-n Spin Relaxation Experiments," Review ojScientific Instruments (in press).

D. R. Davidson, \X'. I'. Summer, and R. C. Reedy, "Measured RadiationEnvironment ai the Clinton P. Anderson Los Alamos Meson Physics FacilityIrradiation Facility," li/fects of Radiation on Materials, Proceedings ol theTwelfth International Symposium ASTM STP 8"(), F. A. Garner andj. S. Perrin,Eds. (American Society for Testing and Materials, Philadelphia, 1985),pp. 1199 1208.

D. R. Davidson, \%\ F. Summer, I. K. Taylor, R. D. Brown, and L. Martinez," 'Rabbit' System for Activation Foil Irradiations at the Los Alamos SpoliationRadiation Effects Facility at LAMPF," Second International Conference onFusion Reactor Materials, Chicago, Illinois, April IV 17, 1986, Los AlamosNational Laboratory document LA UR 85 3630 ( 1985).

D. R. Davidson, W. F. Sommer, and M. S. Wechsler, "Additional Measurementsofthe Radiation Environment at the Los Alamos Spallation Radiation EffectsFacility at LAMPF," Thirteenth International Symposium on the Effects ofRadiation on Materials, Seattle, Washington, June 23-25, 1986, Los AlamosNational Laboratory document LA-UK-85-3502 (1985).

A. B. Denison, C. Boekema, R. L. Lichti, K. C. Chan, D. W. Cooke, R. H.Heffner, R. L. Hutson, M. Leon, and M. E. Schillaci, "Muon-Spin-RotationStudy of ViOy"Journal of Applied Physics 57, 3743 (1985).

J. F. Dicello, M. E. Schillaci, C. W. McCabe.J. D. Doss, M. Paciotti, P. Berardo,andj. F. Dicello, III, "Meson Interactions in NMOS and CMOS Static RAMs,"1985 Annual Conference on Nuclear and Space Radiation Effects, San Fran-cisco, California, July 22, 1985 (to be published in IEEE Transactions onNuclear Science).

J. D. Doss, "Simulation of Automatic Temperature Control in Tissue Hyper-thermia Calculations" (to be published in Medical Physics), Los AlamosNational Laboratory document LA LIR 85-216 (1985).

RESEARCHPublications

J J. Farnum, W. F. Summer, O. T. Inal, and j . Yu, "Quantitative Study, byField Ion Microscopy, of Radiation Damage in Tungsten After Neutron andProton Irradiation," Thirteentli International Symposium on the I:fleets ofRadiation on Materials, Seatile, Washington,June 23 2^, 1 9 ^ , Los AlamosNational Laboratory document LA I' li HS 391H ( 1985).

.'i. Flik.J. N. Bradbury, D. W C'-ooke, R. H. lleffner, M. Leon, M. A. Paciotti. M.F Schillaci. K. Maier, H. Rempp, j . J . Rekly. c:. Boekema, and H. Daniel,"Muon Channeling in Semiconductors: Evidence lor Pionium Formation"(submitted to Physic ill Review 1 c tiers).

G. A. Ciist, S. A. Dodds. D F. MacLaughlin, D. W. Cooke, R. 11. lleffner, R, L.Hutson. M. F. Schillaci. Cl. Boekema..I. A. Myclosh, and G.J. Nieuwenhuys,•'Ferromagnetism in Reentrant /WlrMn ' (submitted to Physical Review H).

K. Hettner. \X\ Cooke, Z. Fisk, R. Hutson, M. Schillaci, J. Smith,.!. Willis, D.MacLau^hlin. C. Boekema, R. Lichti, A. Denison, and J. Oostens, "AnomalousMuon Knight Shift and Absence of Magnetic Order in SuperconductingI', /I'hvBe,," (submitted to Physical Review Letters).

R. H. Fleffner, D. W. Cooke. R. L. Hutson, M. F. Schillaci.J. L. Smith, V, M.Richards, D. F. MacLaughlin, S. A. Dodds, and J. A. Oostens, "Flolmium IonDynamics in 1 ioA.Lu, TRh.,B,,".-!/>/'//«/ Physics 57, 3 I T ( 19HS).

R. H. Hetfner, D. W. Cooke, R. L. Hutson, M. E. Schillaci,... A. Dodds, G. A.Gist, and D. F. MacLau;.;klin, "Muon Spin Relaxation Study of F.xchangeCoupling in Dilute ,4gMn Alloys" Uo be published in the journal ofMagnetism and Magnetic Materials).

R. H. Heffner and D. G. Fleming, "Muon Spin Relaxation: The Technique andIts Applications to Condensed Matter Physics," Physics Today 37- 3H-i6( 198-t).

K. H. Hicks. R. G.Jeppesen, J.J. Kraushaar, F. D. Kun/, R.J. Peterson, R. S.Raymond, R. A. Ristinen.J. L. Ullmann, F. D. Becchetti.J. N. Bradbun,-, and M.Pacioiti. "I'ission of Heavy Nuclei Induced by Energetic Pions," PhysicalRevietvC 31, 1323 ( 198=.).

S. E.Jones, A. N. Anderson, A.J. Caffrey, C. D. Van Siclen, K. D. Watts, J. N.Bradbury, J. S. Cohen, P. A. M. Gram, M. Leon, H. R. Maltrud, and M. A.Paciotii, "Observation of Unexpected Density Effects in Muon-Cataly/.ed d-tFusion." Physical Review Letters 56, 588 (1986).

243

RESEARCHP ,{:<•<• I V i •

M. Leon, "Back Decay and Resonant Hyperfine Quenching in dd\i Fusion"(submitted to PhysicalRerivw Letters),

M. Leon and], S. Cohen, "Ortho and Para-Deuterium Effects in Muon-Catalyzed Fusion," PhysicalRvvicwA 31, 2680 ( 1985).

W. Lohmann, A. Rihbens, W. F, Sommer, ami B. Singh, "Microsiructurt* andMechanical Properties ol Hi)() MeV Proton Irradiated Commercial AluminumAlloy," Workshop on the Relation Between Mechanical Properties and Micro-structure Under Fusion Irradiation Conditions, Riso National Laboratory,Roskilde, Denmark, June 2^ July 2, 1985, Los Alamos National Laboratorydocument LA UK 85 2296 ( 1985).

B. N. Singh, W. Lohmann, A. Ribbens, and W. F. Sommer, "MicrostructuralChanges in Commercial Aluminum Alloys After Proton Irradiation," Thirteenth International Symposium on the Effects of Radiation on Materials,Seattle, Washington, June 23-2S, 19H6, Los Alamos National Laboratory docu-ment LA-UR 85 4<P-i ( 19HS).

W. F. Sommer, W. Lohmann, I. K. Taylor, and R. M. Chavez, "OperatingExperience at the Los Alamos Spallation Radiation Effects Facility at LAMPF,"Thirteenth International Symposium on the Effects of Radiation on Materials,Seattle, Washington, June 23-25, 1986, Los Alamos National Laboratory docu-ment LA-UR 85 3917 ( 1985).

M. S. Wechsler, D. R. Davidson, L. R. Greenwood, and W. F. Sommer,"Calculation of Displacement and Helium Production at the Clinton P.Anderson Meson Physics Facility (LAMPF) Irradiation Facility," Effects ofRadiation on Materials, Proceedings of the Twelfth International SymposiumASTM STP 870, F. A. Garner and J. S. Perrin, Eds. (American Society forTesting and Materials, Philadelphia, 1985), pp. 1 189-1198.

J. Yu, W. F. Sommer, and). N. Bradbury, "Interstitial Dislocation LoopNucleation and Growth and Swelling Produced by High-Energy Cascades,"Thirteenth International Symposium on the Effects of Radiation on Materials,Seattle, Washington, June 23-25, 1986, Los Alamos National Laboratory doru-ment LA-UR-86 679 ( 1986).

RESEARCH

Publications

Accelerator Operations

F. R. Gallegos, L. J. Morrison, and A. Browman, "The Development of aCurrent Monitor System for Measuring Pulsed-Beam Current over a WideDynamic Range," IEEE Transactions on Nuclear Science NS-32(5),1959 19b 1 ( 1985).

G. R. Swain and A. A. Browman, "Proposed Bunching Scheme for a PolarizedH~ Injector," IEEE Transactions on Nuclear Science NS-32, 3024 3026(1985).

H. S. Butler, A. A. Browman, D. C. Hagerman, and M.J.Jakobson, "New750keV H~ Beam Transport Line For LAMPF," IEEE Transactions on NuclearScience NS-32(2), 3086-3088 (1985).

J. W. Kurd, "Measurement and Resulting First- and Second-Order Approxima-tions for a 90° Bending Magnet in LAMPF's750-keV Transport," IEEE Trans-actions on Nuclear Science NS-32(5), 3637-3639 (1985).

S. C. Schaller.J. K. Corley, and P. A. Rose, "Optimizing Data Access in theLAMPF Control System," IEEE Transactions on Nuclear Science NS-32(5),2080 2082 ( 1985).

S. K. Brown, S. C. Schaller, E. A. Bjorklund, G. P. Carr, R. A. Cole, J. K. Corley,J. F. Harrison, T. Marks, P. A. Rose, G. A. Pedicini, and D. E. Schultz, "TheStatus of the LAMPF Control System Upgrade," poster session, 1985 ParticleAccelerator Conference, Vancouver, British Columbia, Canada, May 13-16,1985.

G. Pedicini and J. Corley, "A Central Message Processing Facility" (to bepublished in the Proceedings of the Digital Equipment Computer UsersSociety, December 1985).

G. W. Swift, A. Migliori.J.Wheatly, C. R. Waller, and G. Suazo, "Fabricationand Leak Tight Furnace Brazing of Intricate Objects," Brazing and Soldering8, 32 ( 1985).

R. L. York, R. R. Stevens, Jr., R. A. DeHaven, J. R. McConnell, E. P. Chamberlin,and R. Kandarian, "The Development of a High-Current H~ Injector for theProton Storage Ring at LAMPF," Nuclear Instruments & Methods in PhysicsResearch B10, 891-895 (1985), Los Alamos National Laboratory document LA-UR-84-3043 ( 1984).

245

RESEARCH

Experimental Facilities and Research Support

R. D. Brown, D. L. Grisham, and J. E. Lambert, "Beam Line Windows atLAMPF," IEEE Transactions on Nuclear ScienccnS-52(5), 3812 3HI-i( 1985), Los Alamos National Laboratory document LA-UR-85 I'M"1 ( 19HS }.

G. R. Burleson, W. B. Cottingame, K. S. Cottingame, K. S. D h u g a J . A. Faucett,C. P. Fontenla, J. F. Aniann, K. L. Bondrie, S. J. Greene, C. L. Morris, N. Tanaka,Z. T. Wang, D. Yusnukis, M. Brown, R. R. Ki/iah, F.. C. Milner, C. 1". Moore, S.Mordechai, D. Oakley, P. A. Seidl, C. L. Blilie, D. Dehnhard, S. Nanda, S. |.Seestrom Morris, |. D. Zumbro, and M. Maeda, "A Large Angle 1'ion NucleusScattering Facility for EPICS at LAMPI;" (submitted to Nuclear Instruments &Methods), Los Alamos National Laboratory documeni LA-L'R-86 27H (19H6).

A. M. Gonzales, "Implementation of a Local Area Netwoik at Los AlamosMeson Physics Facility (LAMPF)," in the Proceedings of the Digital Equip-ment Computer Users Society (May 1985).

D. L. Grisham, J. li. Lambert, and W. F. Summer, Jr., "Major Facility Overhaulsat LAMPF," IEEE Transactions on Nuclear Science NS-32(5), 3095.3097(1985), Los Alamos National Laboratory document LA-UR-85-1736 (1985).

D. L. Grisham andj . E. Lambert, "Application of Teleoperator Expertise toRobotics," to be presented at the Robotics 1986 Conference, Chicago, Illinois, April 2O-2H, 1986, Los Alamos National Laboratory documeni LAUR-85--K)66( 1985J.

J. E. Lambert and D;. L. Grisham, "Recent Advances in Remote Handling atLAMPF," IEEE Transactions on Nuclear Science NS-32(5), 3098 3 100(1985), Los Alamos National Laboratory document LA-UR-85 1735 ( 1985).

D. M. Lee.J. R. Bilskie, and G. H. Sanders, "The Response of Drift Tubes toVariations in Wire Diameter and Gas Fillings," submitted to the WireChamber Conference, Vienna, Austria, Los Alamos National Laboratory docu-ment LA-UR-85 1100 ( 1985).

M. VC McNaughton, 'Proton Polarimeters for Spin Transfer Experiments,"Continuous Electron Beam Accelerator Facility (CF.BAF) Summer Workshop.Newport News, Virginia, June 3•", !'>85, Los Alamos National Laboratorydocument LA-UR 85 2161 ( 1985 ).

Z. F.Wang, S.J. Greene, and M.J. Plum, "High-Precision Floating-WireMeasurements of Large nipole Magnets at LAMPF," submitted to NuclearInstruments & Methods, Los Alamos National Laboratory document LAUR-85-3449 ( 1985).

2-16

RESEARCH

Publications

Facilities Services and Program Management

L. Rosen, "LAMPF Its History and Accomplishments," Los Alamos NationalLaboratory'document LA-UK HS .U.^ ( 1985).

Patents

C. Morris, G. Id/orek, and L. Alencio, '^Gated Strip Proportional Detector,"U.S. Patent pending, suhmittedjanuary 19H5.

J. D. Doss and C. W McCabe, "LUectrosurgical Device for Doth MechanicalCutting and C.oagulaiion of Bleeding," U.S. Patent pending, submitted Febru-ary 19HS.

J. D. Doss, "Implantable Apparatus for Localized Heating of Tissue," U.S.Patent pending, submitted May 1985.

J. D. Doss, 'Method and Device for Supporting Blood Vessels DuringAnastomosis," U.S. Patent pending, submitted May 1985.

Status llfLAMPF II

STATUS OF LAMPFII

Accelerator StudiesH A I m---

Summary of ProposedAccelerator Complex

We propose to accelerate protonsfrom <>.K to -|S GeV in two steps.

1. The Iirst synchrotron, a (id 11/rapid cycling booster, is in-jected by every second macropulse of "'y-MeV 11~ ions fromthe existing LAMl'F linac andaccelerates l . iX U)1* protonsper pulse to 6 GeV. The boosterprovides only fast extractedbeams. Fourteen ol eighteen olthe >> GeV pulses CH%) areprovided to experimentalArea N tor neutrino physics.The remaining four boosterpulses (22%) are injected intothe main ring. The proposedlayout of the accelerator and ex-perimental areas on the LAMPFsite is shown in Fig. 1.

2. The second synchrotron ac-celerates 6.0 X 1()'3 protons perpulse (four booster batches)from 6 to 45 GeV at i.i3 Hz.The main ring has slow extrac-tion only, with a 50% macroscopic duty factor. The slow-spill can he done in two modes,fully debunehed with a microscopic duty factor ol ioo%, orwith rt on, giving 1.75-ns pulse(FWHM) every 16."1 ns(59.8 MHz). A summary of theparameters of the proposedLAMl'l' II accelerators is givenin Table 1.

The experimental areas ofLAMPF II fall naturally into twoclasses. The secondary hadron beamsare all produced by the -i5-GeVproton beam and are located in theexisting high energy experimentalhall, Area A. In the upstream thin-

reaH

-Conliolf li RnornPSR

FIGURE I Site plan ol 'he proposed LAMPF II .'iccoleratcrc; and e> per

250

STATUS OF LAMPF il

target portion of Area A, facilities areprovided for Drell Van experimentswith-o i'ieV protons. Neuirinoexperiments will be performed in a newexperimental area, Area N.

The proposed LAM IT 11 accelerators are simple and conven-tional. High intensity is obtained byrapid cycling. This '"bnite-torce"techrique requires larger rf voltagesand n ore rapid transfer of energy tomagnets than in other high energyaccelerators. However, the circulating current is similar to existing machines, allowing reliable extrapola-tion of accelerator physics to theLAMIT 11 design. Technology devel-opment is limited to producing efficient and cost effective designs; nonew ground needs to be brok' 'i incontrol of high intensity phenomena.Our choice ot operating the mainring above its transition energymakes the beam stable against microwave instabilities without an artificialincrease of the longitudinal phasespace.

Our accelerator and experimentalarea parameters are the result of anextensive discussion in which phys-ics output and cost were the mostimportant factors. Our basic strategyis "o build a full set of experimentalfacilities in a single slow extractedbeam area. Vi'e base proposed a simpie high energy accelerator that hasthe possibility of significant upgradesin [he lulure. This strategy more thandoubles our efficiency in usingprotons to produce secondary beams,allows maximal physics output in theearly years, and promises upgradeslater to the less activated portion ofthe facilitv. namelv the accelerator.

TABLE i L i s t <r« I •'•

l-v.'pi":!.|i:ji'i rath; (I i..']I i A ' t l " ! •-)! pr.-.t.-in.-. p i | l -

C . j l ' r ' n l | | i - ' - )

C iir I'-n!^'^"'1 ".^ (n-.|

H. I ' I J O ' T ' I I ti.ir^'

, i T t l . d l ' ! '• '•

OudruDOlesr iuniue'

Magnet waveformRise time (ms)Fall time (ms)

a The beair , l J '"J i ' 'Ui'1O f

"-'pi.=i-,i e-"a:.! '0 r i '"Ocie

Two types of upgrade to theLAMPF II accelerator are possible inthe future. The intensity can be increased by a factor of 3 to lot) |AA bythe addition of a collector ring and astretcher ring. No changes to thebooster or main ring will be requiredby this inf .sky upgrade. The secondpossibility is to raise the final energyto 60 GeV. The nominal 1,5-T bending magnets of the main ring are designed for later operation at 2.0 T at acost of a factor of 2 in magnet power.

New features are presented in thisproposal that represent significantchanges Irom the previous version.

• The users of LAMPF II will noticemost the fully debunched slowextraction option with 100%microscopic duty factor.

', 1 .'') ' h ()

1 5 X 10 ' '

M.-jiri Rinq

I, !) -15 0

0 X U ) '

4 '•<

.:2-i i

Gmuso1 1 "

05 ',

idal

0B 0

225 1 503

72

1 inoar5050

T t o f ' h e GlQA1 (?• t f 3 ' . t - o n m o d e 0 D * ? r a d o n •

251

STATUS OF LAtHIPF II

• The fast feedback around the rfamplifier will lower ihe effectivecavity impedance to enable de-bunched slow extraction, and itwill also allow higher beam load-ing, which will reduce rf costs(both capital and operating) by30% or more.

• The newly proposed separatedfunction lattices have more flex-ibility for unforeseen operatingmodes, can be upgraded tohigher final energy, and have alower operating cost than theprevious combined-function ver-sions.

• We have increased the length ofthe straight sections of the mainring, allowing the possibility ofSiberian snakes to avoid al-together the problems of cross-ing depolarizing resonances.

• And finally, the new single high-energy experimental area usesthe available protons more effi-ciently, which is the equivalentof a 2-times-higher beam currentthan that in our previous version.

Also, technical improvements inthe accelerator design have beenmade that will be less visible to theusers but will contribute to morereliable operation or greater flex-ibility in the future.

To begin with, we consideredmany alternative designs. Becausenone of these was more cost effectivethan the proposed two-ring design.

we now have greater confidence thatwe are moving in the right direction.

The lattice designs have beenchanged from combined function toseparated function. This change al-lows the use of more symmetricmagnets with smaller undesiredmultipole errors, reduces storedenergy in the dipoles, and enables usto better predict the expected fielderrors. We have tracked both ringsusing realistic error estimates andfound that the dynamic aperture islarger than the worst-case phasespace, even with 4 times the expected magnetic field errors.

The injection scheme has beenstudied in more detail. Simulationsnow include "plural scattering" andthe long tails of energy loss caused bydelta-ray production in the stripperfoil. Experience with the ProtonStorage Ring (PSR) shows that thelifetime of 300-u.g/cm2 carbon foils isnot a problem, even with a muchlarger circulating current, more foilhits, and a smaller foil than thatproposed for LAMPF II. The halo fac-tor has been raised from 2 to 4because simulations showed that thiswould be necessary to keep lossesdown to a few tenths of a percent.

We have made significant progressin our study of instabilities. We nowhave a calculation of the expectedlongitudinal and transverse im-pedance of both rings, using realisticelements that include kickers, rfcavities, and beam monitors.Bunched-beam instabilities havebeen considered in addition to the

252

STATUS OF LAMPMI

Accelerator Studies

coasting beam instabilities discussedin the previous proposal. Numericalsimulations have been done, both forthresholds and for growth times ofimportant modes.

Our work on the rf system hasprogressed in several importantareas:

• we have calculated the modespectrum with two and threedimensional codes and havecompared the calculations withmeasurements on a full-scaleprototype cavity;

• the rf test stand has been com-pleted;

• full peak power has been delivered to a dummy load; and

• a full scale cavity has been constructed and all components,including ferrite and BeO cooling rings, aie on site. First tests ofthis cavity with ferrite are ex-pected by April 1986.

We have begun a study to deter-mine feedback-control requirementsfor the rf system and to see how thissystem interacts with beam stability.We have selected fast feedbackaround the final rf stage because thisgives the best stability. Our designincludes the capability of operatingthe cavities with very low fundamen-tal voltage, as would be required during extraction from both rings andinjection into the main ring.

The ac power system has been investigated in further detail. Ciearly,an additional pov. r supply to LosAlamos County is required. The Labo-

ratory grid is adequate to distributethe power on the Lab site, but a new1 IS- to 13-8-kV substation is neededfor the addit. nal average power. Thelarge pulsed load of the main-ringmagnets must be filtered locally. Wehave commissioned Brown Boveri tostudy .he capability of a generator tohandle the pulsed load. A 13()()-MVABrown Boveri generator was chosenfor the design study becauseGroup CTR is planning to install thatgenerator in Los Alamos for a compact torus experiment and it therefore may be available to us whenLAMPF II goes on line in late 199-1.

Control of High-IntensityBeams

High initial intensity is of littleoperational use unless beam spillsare acceptably small. We intend tokeep general losses to a level of 0.1%so that hands-on maintenance of theaccelerators will be possible. Forlosses that cannot be prevented, suchas those in the injection and extrac-tion hardware, local shielding andspecial remote-maintenance facili-ties will be provided. One-turn, fast-abort dumps will protect the ma-chines from accidental spill of the''pfire beam, and emittance-definingcollimators downstream of the ex-traction systems will protect the re-

253

STATUS OF LAMPF II

maining hardware from scattering inthe extraction system, emittancegrowth, and general halos.

A number of design features arebuilt into the machines to facilitateminimum loss operation. Above all,good diagnostics will be providedthroughout the facility, including thepossibility of full measurement of thephase space and orientation in bothrings and all transfer lines. The 11"injection system allows full control olfilling of the injected phase space inall six dimensions. Halo strippers areprovided to clean up the long tails ofthe linac beam, and dumps will catchany unstripped H~or H"beam.

Our bunch-to-bunch transfer fromlinac to booster and from booster tomain ring will minimize capturelosses. By filling less than 50% of therf bucket, we can prevent losses dur-ing the nonadiabatic transition fromcoasting to acceleration in both machines. Gaps in the beam ( ~sixempty buckets) will be provided sothat single-turn transfer betweenrings and fast extraction will bepossible without losses.

Large apertures and conservativelow-tune shifts early in the accelera-tion cycle will minimize space

charge problems. Low Rs/Q (shunt-impedance/resonant Q) cavitieswith fast rf feedback around the finalamplifier and cavity will preventlosses associated with the Robinsoninstability. The proposed ceramicbeam pipe with conducting stripseliminates troubles from multipolesproduced by eddy currents of therapid-cycling guide field and theneed fora low-impedance beampipe. Active dampers will beprovided to eliminate the coupled-bunch instabilities that cannot bestabilized '~>y control of the beam en-vironment. The special high-betastraight sections of the main ring aredesigned to minimize losses at theslow-extraction septum and also atthe magnetic septum, which will beplaced 90° downstream of the elec-trostatic septum.

The minimization of losses i.-> acontinuing process of attention to de-tail, training of staff, and possibly theuncovering of new accelerator phys-ics problems. The experience to begained at the Los Alamos PSR, whichrecently set a new record of 30-u.Aaverage current delivered to ex-perimenters, will be invaluable inminimizing the commissioning timeand beam losses of a high-intensityfacility such as LAMPF II. The con-tinuing beam-availability record ofLAMPF indicates that the Laboratoryinfrastructure, the staff, and the injector are ready to meet the challengesof high-intensity at LAMPF II.

254

STATUS OF LAMPFII

Accelerator Studios

Comparison with Existing andProposed Accelerators

The parameters o! a number ot existinj; and proposed high intensitymachines are shown in Table II.

The circulating current oi bothLAMPF II machines (2.2 A) is onlyslightly above the CliRN ProtonSynchrotron (1.6 A) and is consider-ably less than that already achieved atthe Los Alamos PNR (9 A). The circu-lating current is a good measure ofthe trouble to be expected with H~injection foil lifetime and scattering,

and is also important in determiningthe instabilities to be expected.LAMPF II looks like a reasonablechoice based on this criterion.

The users' measures of machineperformance are secondary beam fluxand duty factor. Averaged over thepast few years, the typical operatingmode for high-energy machines,such as the Brookhaven AGS, hasbeen, roughly, 50% slow-extractedbeam and 50% fast-extracted beam.Tor this kind of schedule, theLAMPF II proposal of simultaneous6-GeV fast extracted beam and 45-

T^BLL : Para^tjters 0! P'oton

A , , : - . . « . . , * . . - . . . * : • • , • : . . . ,

Synchrotrons

P-otonEnergyiGev)

i") c i

Protons/Pulse

0 17

DutyFactor

0 00057

CirculatingCurrent

(A)

2 3

RepetitionRate(Hz |

30

AverageCurrent

811 ^ i j t ' r r r '_•. [' • • > - ! ( ' P f j : \f

-accatorr.'pi.von

0 5(0 8) 0 5( 0 0032 0 5(6 1) 50 17(200)

Fer.rTiiiab Booster

^ EK ProtOn Synchrotron

CEPM Pr'>ton S/nchrotron

B ' O O l - r ' 3 ; P O •-"' l l e r r i -a l i r •• j

Gradient Gvr~chr:jtron 1 -"• C-ir

r P' . ','F 'f a<?<" F.;ir|---r , ' '

0 8

8

i 2

2 6 D

2 6 b c

::, 2 " 5 D

30 h

30 D

b ^4 5 "

3is afpinDafomheses)tC'Derating rrodPs not a-/ai'aljie simultaneously

~No longer a-va^abie tor e/oer'^ienlsaSn-tiiar to the European Hadr on Fac9Dua' e-e'gy beams available simul

ihty

taneously

1 5(5)

0 3

0 4

o o

05

1 64

66

1 56

0 00032

0 0024

18

0 0001450

0 0001850

0 00361

0 006750

9(27

0 3

0 6

160 4

1 00.7

CO C

O

CJ

C-J

2 22 2

12

15

0 6

0 670 38

0 670 38

1010

6010

30(100)

7 2

0 32

2 305

1 80 73

100100

14432

255

STATUS OF IAWPFII

Accelerator Studies

TABLE HI Normalised field Irom

(1

Brookhaven AGSf 1984)a

TRlUMF Kaon Factorya b

LAMPF II c

aAssumes 5 0 * slow extraction 50'/. lasil

^identical to the Furopean Hadron FacilitycSimultaneous slow and fast e n a c t i o n

Existing and

K"GeV/c) (/

1139100

uMMCliun

Pioposed Kaon \ actones

Yield per Year

K" p'GeV/c) (7GeV/c)

1 1161 17618/' ^'yo

(Integrated)

16861

GeV slow extracted beam wouldyield essentially the same duty factorand beam flux as the TRlUMF KaonFactory. In addition, the high-energy(45 GeV) LAMPF II beam is morefavorable for DrellYan physics, high-energy kaons, and antiproton produc-tion. The low-energy (6-GeV/ fast-extracted beam is preferred for neu-trino oscillation experiments. A com-parison of the expected yield ofsecondary and tertiary beams fromseveral kaon factories is shown inTable III.

In comparing the LAMPF II andother kaon factory proposals, oneshould take note of the followingtechnical points:

• The LAMPF II magnet aperturesinclude a factor of 4 increase inacceptance for clearance of thebeam halo. Experience atLAMPF indicates that largeapertures are necessary to ensurelow losses.

° The LAMPF II rf buckets will befilled to no more than 50% inorder to avoid longitudinal lossesthat begin at 65%. The 33%

bunching factor used in thespace-charge calculation is theresult of a Monte Carlo simula-tion of the proposed injectionscheme with 50% bucket filling.

• The LAMPF II cavities will betuned with perpendicular biasedferrites that have extremely lowlosses. The natural RjQ of thecavities, which is approximately35 ft, minimizes beam-loadingproblems. Because of theperpendicular bias, a muchhigher bandwidth is possible inthe bias field (Fermilab cavitieswould have trouble providingthe rapid tuning required in a 60-Hz machine). Thus, theproposed LAMPF II rf system isthe best choice from the point ofview of efficiency, beam loading,and tuning bandwidth.

• The low-7, main ring proposedfor LAMPF II results in betterstability at extraction time thanan infinite-y, main ring.

e The linear-ramp power supplyproposed for the LAMPF II mainring is more flexible than the res-onant system. In particular, frontporches and variable repetition

256

STATUS OF LAMPFII

Acceleraioi' iti idies

rates can be easily ohtained. Also,we have calculated that this system is cheaper initially and usesless operating power,

• The two ring machine proposedfor I.AMPF 11 will be easier tooperate than any other kaon fac-tory machine. LAMPF II will alsohave smaller beam losses be-cause of fewer transitions between rings, which cause signifi-cant operating problems, emittance growth, and beam losses atall existing high energy facili-ties.

Alternatives

The proposed two ring design forLAMPF 11 is the most cost effective ofmany scenarios considered. Weenumerate here those alternative ver-sions that were studied to the level ofa cost estimate and the factors thatled to their rejection.

Early designs for LAMPF II usedone ring. These designs had to contend with a large phase space accep-tance, crossing transition, and veryhigh rf voltage with broadband tun-ing. The best version was the -o-GeVvariable transition energy design ofFranc/ak.1 Our cost estimate in-dicated that the one ring design is150 million more expensive than theadopted design.

Another scheme for eliminatingthe booster involved building a newhigh-energy linac to replace LAMPFas an injector. A cost-optimized injector that would fit into the LAMPFtunnel is a 3.7-GeV linac. This linacwould have to deliver 797-MeV beamto the PSR, 200 |iA to a neutrinotarget (the same beam power as thatfrom a 6-GeV booster) and 3-i |*A(chopped) to the LAMPF II mainring. The installed cost of a 3.7 GeVlinac is estimated at $HH million(1985 dollars without contingency),compared with the $42 millionbooster replacing it in the currentproposal. The use of 37 GeV H~causes some problems that have notyet been solved, it requires a largeradius-of-curvature switchyard thaimakes reuse of Area A impossible,and it requires a much longer shut-down of the PSR than would our two-ring proposal.

One of the reasons that the high-energy linac option is expensive isthat it must give a high duty factorand serve several users simultane-ously. A way around these problemsis to provide a linac in the injection

257

STATUS OF LAMPF II

-

•

\

\

-

tunnel to raise the injection energy ofLAMPF 11. We have done a cost tradeoff study of this option. The total costof linac, booster, and main ring isshown in Fig. 2(a); the linac powerconsumption is shown in Fig. 2(h).The optimum energy for injectioninto the booster is so close toS()() MeV thai it is not worthwhile toconsider the complications of an ad-ditional linac in the injection chain.

Both the TRIUMF and EuropeanHadron Facility groups haveproposed accelerators with a dc col-lector ring between the booster andmain ring and a stretcher ring toachieve 100% duty factor. We havestudied this scheme for LAMPF II andfind that to achieve 67 (iA at 4 5 GeVcosts about $30 million more for material than would the two-ring, 3-I-|AA

design. Because the dc rings usecomponents (magnets, rf, vacuum,etc.) that are different from the rapidcycling rings, at least a 200 man-yearper ring cost would be incurred inengineering design and inspection(ED&I) and installation. The dc ringsnot only will raise the initial cost butalso will make rapid construction ofthe machines very difficult and ex-tend the commissioning process. Wehave chosen, instead, to makeprovision for a later upgrade by add-ing collector and stretcher rings.With these additions, the output current of LAMPF II at 45 GeV can beraised to 100 (iA without booster ormain ring changes.

Recently, the suggestion has beenmade that a superconducting linacmight be an attractive alternative.Proven designs at 5 MeV/m gradientexist, with greater than 20 MeV/rndemonstrated in single cavities. Kecirculation of protons looks difficultbelow velocities of 0.9999 times thespeed of light (65 GeV). Thus weconsider a single linac of i5 GeV. At20 MeV/m, a 2.25 km linac would berequired. At $100 thousand permeter, the structure alone would cost$225 million. This amount equals theapproximate cost of the twoproposed synchrotrons, includingbuildings, installation, ED&I, projectmanagement, and contingency.Thus, at the present time a supercon-ducting linac appears to be morethan twice as expensive as theproposed rapid-cycling synchrotrons.Should a major breakthrough insuperconducting linac technologyoccur, we will reevaluate this option.

One possibility tor a cost-eflectivemachine is still to be evaluated.Superconducting magnets for themain ring might allow a shorter tun-nel and lower operating cost thanwould the proposed room-tempera-ture main ring. A careful study isneeded to determine whether thesuperconducting magnet alternativeis more cost effective than room-tem-perature magnets. We expect to studythe superconducting magnet optionin the next year.

Reference

1. B.J. Franczak, "Transitionless Lattices for LAMPF II," Los Alamos NationalLaboratory report LA-1O26O-MS (October 19H4).

25H

Facility Development

Nucleon Physics Laboratory Upgrade

Spectrometer Calibration at EPICS

Radiation-Eflects Facility

DaL.- \nalysis Center

LAMPF Computer-Control System

FACILITY DEVELOPMENT

Nucleon Physics Laboratory (NPL)Upgrade

Introduction

LAM PI1" has embarked on a major 3year development program toenhance ongoing experimental programs and to provide facilities fornew physics research in nucleoncharge exchange reactions' in theNuclear Physics Laboratory (NPL,Area B). Central to this developmentis a high-intensity polarized ionsource, a medium resolution proton

Neutron Time nt FlightFacility (NTOF)

in invlei iMRGl

LmeBiV/

Tunnel

spectrometer for ({>,}>') and ( n,p) re-actions, a 6()() in neutron flight pathwith a beam swinger for (j>,n) reac-tions, a high-resolution iv.omic beamfacility, and beam-lint* modificationsto deliver beam to these areas.

General management responsi-bility for the upgrade project lieswith L, Agnew, Associate divisionLeader for Experimental Areas, andthe Experimental Area DevelopmentCommittee will review progress.R. Werbeck is the TechnicalCoordinator, with the following pro-ject managers:

J. Donahue (MP 7) •- Beam-LineModifications and High-Resolu-tion Atomic Beam (HIRAB);

J. B. McClelland (MP-10) —Neu-tron Time of Flight (NTOF);and

R. Boudrie (MP-10) — Medium-Resolution Spectrometer(MRS).

User advisory panels have beenformed to provide input from thescientific community and to serve asa board of review for plans and op-tions. Advisors for NTOF areS. Austin, A. Bacher, C. Goodman,J. Moss, and C. Zafiratos; advisors forMRS are G. Crawley, C. Glashausser,G. Glass, D. Lind, and J. Rapaport.

Facility Upgrade

The (p,n) Facility. One of theearliest possible additions to the NPLcould be a beam swinger and neutrontime-of-flight (NTOF) facility for(p, n) reactions. The primary protonbeam would be directed into thebeam swinger area by a switchingmagnet (Fig. 1). Quadrupole

FlF.-il.ih'> ' lL>npn<;ecJ rnodilicatinn" of the f |f'i .n

262


, .!• . i l •• -r _ j T - i , : i r u I , •

1- ' 1 1 .!'•' i ' I ' A ' I ' l l ighl (MTOF ) pcJll'i rjru

magnets will maintain the locus onthe ifi.n) target as the swinger angleis varied. Beam line instrumentationwill he similar to the existing inventory wire chambers, ionizationchambers, and polarimeters for de-termining beam profile, intensity,and polarization.

The beam swinger would be ;i livemagnet system lor varying the inci-dent angle of the proton beam on the(/».»/) target, effectively changing [heneutron scattering angle while keeping [he neutron flight path and delectors stationary. As currently envisioned, this system will allow formomentum transfers greater than^ fm~' at all energies between 2(10and H00 MeV. The fourth magnet ofthe swinger would aim (he proton

beam into a beam dump capable otstopping and shielding up to 6()0 nAof 800-MeV protons. The swinger,(p, n) target, and beam dump willreside in a shielded crypt appendedto the EPB room, as shown in Fig. 1.

A flight path of up to 600 m wouldbe possible with some excavation(see Tig. 2). Given the expected tiniing performance of the acceleratorand detectors, this will yield neutronenergy resolutions of 1 to 2 MeV at800 MeV. This is consistent with(p, n) work being carried out at otherlaboratories at lower energies. Beamtiming characteristics will bemonitored using beam microstructure pickoffs, such as those used atthe Weapons Neutron Research(WNR) facility. These were tested in

263


Niucleon Ph\Su:s L jboiaio

Line C during the 1985 productionperiod. Polarized beam wouldusually be chopped at 100 ns for neu-tron timing.

The detector hut will be a -»• by 10nr portable house, on a carriage sothat it can be positioned at three orfour predetermined locations alongthe 600-m flight path. It would be aself-contained unit, housing the delectors and their support systems,electronics, and the computer-acqui-sition area. Alternatively, the acquisi-tion station could he separate, hutmove in tandem with the detectorstation.

Medium-Resolution Spectrometer(MRS). A medium-resolution spectrometer, A£ ~ 1 MeV, would haveseveral roles. It would

1. complement the HRS with highacceptance where 1 MeV re-solution is adequate, possiblyserving about half the HRSqueue;

2. serve as a home base forpolarized-target and light-nu-clei experiments that cannot exploit the HRS energy resolu-tion; and

?. serve as a detector for (n,p)studies with resolution wellmatched to the narrowest available neutron spectrum.

The MRS would occupy the presentEPB area most of the time.

Design work has proceeded for theoptical performance of such a spec-irometer. The design goals thai wereconsidered are listed in Table I. Be-cause the instrument will be used tomeasure the polarization ofihe .it n-tered particles, the net angle of de-flection should be small, ideallyabout 15°. This will ensure thai for allmomenta considered there will be nodead spots in the polarizationanalyzed (that is, the outgoingpolarization will not be precessedsignificantly into the longitudinalcomponent at the focal-plane detect-ors). The demands for a large solidangle and reasonable resolution,taken together with the small net de-flection angle and focal-plane angle,will be difficult to meet.

Fourdifferem layouts were iried,each with a large number of varia-tions:

1. a QQDQQ system,

FIGURE 3 Layout for (he QD( -D) system of Med ium-Reso lu t ion Speclrorn<>ii

264


n ItiySics I aburdlory (Jpyrade

TABU: i Medium HeTi ;pectio/)ielt!i Design Reqimemenis

Over-ii' vwitr

Fu'l •'•. -'i.'t.in, >' i. it - i l l i '.M l l l h . !i Ml ,111

R e c i u - i t -•,- . ^ L i t . - i f u ,•

iyoo Mi'v.o ioOy in

11 -i i.

I ' ) I Tl ; I

±1 I!

•) 0-1 '11) insi+.1 nn,'HI

(800 MeV deuleioiil

(±i':.(>Mt!V)(b Mev!

(±L.'O M(0 5 K

2. a QDQ system with a strongnegative n value,

3. aQDl D) system with strongwedge focusing, and

4. a QDS system with a strongnegative n value.

The QDI D ) system is the mostpromising (a layout is shown inFig. 3) Kay tracing calculations arein progress. One issue is perform-ance with a large target area( — 2S cm") for the ( n,p) capability.Additional requirements to be ad-dressed are improved small-anglescattering coverage, localized targetshielding a generalized second arm,a focal-plane polarimeter, and a non-magnetic pivot to accommodate apolarized target. The spectrometerfacility will require a permanentcounting house.

The first expected use would be on(p,//t reactions During this time theeffects of a large target area as-sociated with the (>i,p) reactionwould be studied. The initial imple-mentation of a neutron source for

(n,p) experiments might best hedone using the existing BR neutronchannel, replacing the LD, targetwith a thin lithium target This wouldproduce a nuclear-physics gradeneutron beam with an energy widthless than 1 MeV, and implies movingthe MRS between EPB and BR, whichis an advantage from another point ofview. It would allow the MRS to beused in nucleonnucleon programsin the BR, for which a keen interestwas demonstrated during the NPL up-grade workshops. Because the wallseparating EPB and BR is movable, itwould be reasonable to move theMR? on air pads between the twoareas on a cycle basis. When the in-itial phase of the ( n,p) program in BRis completed, a decision can he madeas to the best targeting scheme forthe program in general. A possibilityexists to target the proton beam inEPB about 2 in upstream of the ( n,f>)target, then "dogleg" it around theMRS and restore it in the EPB dump.

265


j i : • v

This is similar to the system beingdeveloped at TRIUMF for a similarapplication at lower energies. Therequired shielding configuration isnot yet clear.

Future studies involving polariza-tion transfer might use the ratherlarge values of Du for lithium ( ~0.5at 800 MeV) in conjunction with neu-tron spin precession and the MRSfocal plane polarimeter. However,the reduced counting rates as-sociated with polarimeter efficien-cies may require further develop-ment. This facility—a polarizedmonoenergetic neutron beam, aproton spectrometer, and apolarimeter—would be a powerfuland unique tool forspin-isospin nu-clear physics, highly complementaryto the ip,n') program beingproposed, as well as to the (/< / /)program at HRS.

High-Resolution Atomic-Beam Fa-cility. The prime goal of the neutralparticle-beam program is to assessthe feasibility of using neutral par-ticle beams as directed energy weap-ons outside the earth's atmosphere.This initiative calls for a significantlyenhanced program of technologicalfeasibility demonstrations. The High-Resolution Atomic-Beam (HIRAB)facility will provide the capability tostudy beam sensing and control. Awide range of basic atomic physicsissues can also be investigated withunprecedented precision.

The project will provide for theconstruction of a l600sq-ft air-condi-tioned building. . 20- by4O-by4-ft-thick concrete pad, isolated from theNPL building slab, will provide vibra-

tion isolation for the laser and optics.A movable beam plug upstream ofthe facility will allow it to be oc-cupied while the other areas are be-ing used.

Beam-Line Modifications. Asshown in Fig. I, HIRAB will receiveundeflected H~ ( P~) along the pres-ent EPB line. A switching magnet willdirect the beam toward the MRS orNTOF; thus use ordinarily will heexclusive. The only interference withpersonnel access to areas not receiv-ing beam will come from the trans-port of the HIRAB beam near MRS.

A shielded extension of the Line Btunnel into the EPB area will enclosethe switching magnet and beamplugs for each line. Upstream of thes vitching magnet, the EPB line willremain much the same.

The 52-in. cyclotron magnet ac-quired from the University of Colo-rado will be the switcher, bendingthe beam 29° to the left toward MRSor 28° to the right toward NTOF. TheNTOF line will continue through a 7°bend to the right into the new NTOFswinger crypt to be built east of theEPB area. The undeflected beam willpass through the MRS shieldingenclosure into the new HIRAB build-ing that is to be constructed northeastof Area B (at the present EPB beam-stop location).

The switching magnet and beamplugs will be enclosed in a mini-mum-thickness concrete house. Theshielding will be kept to a minimumto reduce the amount of floor spacelost to the MRS area in the building.This effort to maximize floor spacefor the MRS precludes space for the

266


installation of phase space tailoringcoilimators tor MRS and NTOF. Future collimator installation would re-duce the angular range lor the MRS.

Once beyond the Line B tunnel extension, each ol the three transportlines w ill contain beam instrumentation, a quadrupole doublet ( availablefrom -.urplus ). and a vacuum system.Each beam line will ultimatelyterminate in a beam stop capable ofstopping SL'\ eial hundrednanoamperes ol protons.

The MKS enclosure will be lightlyshielded along its sides and will have-no shield root above it. Thus, eventhin MRS targets will need to belocally shielded in order to run a fewnano.unperes oi beam into them. TheHIRAB enclosure also will be thinlyshielded along its walls and will haveno shielding in the roof. However,HIRAB will not use solid targets, sonot much shielding is required. Theswinger crypt for the NTOF facilitywill he a relatively well shieldedenclosure I includin;', a shieldedroof I that will permit several ruindred nanoamperes of protons tostrike targets up to 1 g/cm2 thick. Thecrypt will be quite large (12 by 7.5 m)to accommodate the motion of thelarge swinger magnets. Much of ihcshielding will be reused surplusshielding from the University ofColorado 52in. cyclotron facility andfrom Area A of LAMPF.

Experiments also can he run in theEPB area, more or less as done cur-rently. During such periods, the MRSwould have to be rotated out ol theway of the experimental setups. Amovable beam stop upstream ofHIRAB will allow HIRAB to be anopen area.

Implementation of the new lacilities will be staged over several years.During the 1986 shutdown (Januaryto mid June 1986) the switchingmagnet and the three movable beamplugs will he installed and enclosedin shielding. Some of the modifica-tions to the Area B building neededfor the completed NPL upgrade project will be started (for example, theaddition of personnel access doorsand the removal/relocation of elec-trical breaker panels and transformers). The present EPB beam stopwill be moved, and work on theHIRAB area will start. During the1986 production cycles, the EPBmain area will be available for experimental use.

267

FACILITY DEVELOPMENTPhy cs I aboMtorv

Workshops

On December 16 and 17 of thispyst year, a second workshop dealingwith these major upgrades of the NPLat LAMPF was held, with 6() partici-pants representing 22 universitiesand national laboratories. Thepurpose of the workshop was to review the extensive planning and design that had taken place within thelast year and to make final criteria anddesigns for completion ot the project.Working groups were established forlong-term projects such as detector

development, beam diagnostic in-strumentation, and spin-precessionsystems. There was general agree-ment on work done to date on beamline modifications, the Medium-Re-solution Spectrometer, and the beamswinger and flight path for the Neu-tron Time of Flight facility.

Within the funding schedule andmanpower for this project, it is ex-pected that the neutron (light pathand swinger will be available in 19H7,and that the spectrometer and newion source will be available in 19HH.

Reference

1. J. B. McClelland, A. Bacher, R. L. Boudrie, T. A. Carey, J. Donahue, C. D.Goodman, et al., "Development Plan for the Nucleon Physics Laboratory(NPL) Facility at LAMPF," Los Alamos National Laboratory reportLA-10278-MS (February 1986).

268



The floating-wire technique hasbeen used to measure the particlemomentum versus magnetic fieldcalibration of the spectrometer atEPICS.' Orbits through the dipoleswere measured in situ over the rangefrom 233 to 659 MeV/c. The measure-ments were corrected for gravitaiional and frictional effects.

If a thin, flexible wire of negligiblemass carrying a current / issuspended with a tension Tina mag-netic field B, it will follow a pathdescribed by the differential equa-tion of motion for a particle withcharge q and momentum P in thesame field, provided no other forcesact on the wire. The relationship


Alignment Bars

• Floating-Wire

•Weight (T,

FiGuPE 1 Si- etch ol the spectrometer dipoles at EPICS and schematic ol the lloatmg-/.' fe :. ,s!r<m fhe .e-ticai bend angle is 120 DCPS is the direct-current powersuop', ara O'/M is the digital voltmeter

269


among the quantities is

f(MeV/c) T( grams)

<y (electroncharge) / (amperes)

Because the spectrometer bendplane is vertical, the path of the wiremust be corrected for distortion induced by gravity.

An apparatus, shown in Fig. 1, wasdesigned to measure the entranceand exit trajectories of a 0.025 mmCuBe wire with measured tensionand current for magnetic field H from6 to 17 kG. A frictionless air-bearingpulley was used for accurate tension-ing. The wire weight distortion isshown in Fig. 2. The distance AS'in the figure is the calculated

• Heavy wire

Simulated wire

• Central orbit

Units are multiples 2of R(=129.7203 cm)

F5(X)

FIGURE 2 Schematic diagram ol the speclrometer divided into live regions, rind theoaths ol the central ray, simulated wire, and heav, wire from the image plane throughthe spectrometer tc the focal plane

270


]| IH' .trorni >tcr ! .,ililji;ili(jn ;jt I I 'I'

difference, in the midplane, betweenthe actual wire location and that for amassless wire Measurements of thisdistance as a function of tension compared well with predictions.

l:rom these measurements thequantity HI'c for the central ray wasdetermined. This quantity is used bythe kinematic routines in determining magnet settings for the spectrometer The momentum dependence of this quantity is neitherconstant nor linear, as currently implenu'iited in the kinematics calculalions. The method of measurementand the implications of the results arcunder consideration. The averagevalue of the redetermined H/l'c is25."25 G/MeV/c witho( li/Pc) = 0.005, to be comparedwith the previously determined valueof 25.63 G/MeV/c. The comparisonis shown in Pig. 3.

This new calibration is currentlybeing used for development scan-ning of the channel output momenturn at EPICS with respect to magnetsettings.

u

a'

LH-\

• b

EPICSB/Pc

- Floating ,',

Gurrehti

Mo

ire MftfiUihTUHnl -

J—i—i

,' iriipien>".ti.ii ii i i

mentum Pc

FIGLIRE 3

Reference

1. Z.-F. Wang, S.J. Greene, and M. A. Plum, "High-Precisinn Floating-WireMeasurements of Large Dipole Magnets at LAMPF," Nuclear Instruments &Methods (in press).

271


Radiation Effects Facility New Facility at Beam Stop,V F Sornrnyi i k T.-ivlnr and R tv

•s. have; (Los AUnux,)

Installation of new hardware atTarget Station A 6 for radiation damage effects studies was completed inMay lWS F.xperiment capsules maybe introduced into the secondary par-ticle flux emanating from the interac-tion of the primary proton beam withthe isotope production targets andthe beam stop. Twelve independentinserts are available for irradiations in

the secondary particle flux. Figure 1shows eight of the inserts and theirrelation to the isotope productiontargets and the beam slop. Also, threeinserts allow positioning of irradia-tion capsules into the direct protonbeam. Figure 2 shows the position ofthese capsules in the overall layout ofTarget Station A 6.

During the period from May to De-cember 1985, four proton irradiations(LAMPF Lxp. 769) and two neutronirradiations (Exps. 936 and 769) werecompleted. Control equipment, a

CopperBeam

Stop

Neutron •Producing.Targets in the Isotope

Production Facility

Gas, '/VaterInstrumentationPassage toLaboratoryAbove

Water-CooledShielding

Irradiation Volume~ 12 7 by 25 by 50 cm12 Places

9 Disl-s, 7 6cmdiam

Equally Spaced

^

FIGURE 1 t leutron irradiation inserts at LAMPF Target Station A 6 and Inur iRlatio 11'.isotope production targets and the beam stop Shown ate 8 ol the 12 inserts ear11 Ant'experiment volume ol about 0 02 m !


closed-limp helium heat sink, and aclo.-.ed-luup water heat sink for ternperature control were made operational. instrumentation racks tor thisequipment are located directlyoutside the Target Station A <> concrete hut and are accessible during

beam-on operation.Experiment changes were made

during periods between cycles aswell as on a maintenance day. It wasdemonstrated that an experimentchange can be accomplished in (i h.

-- i j o s e i ! 1 in)|j i l ev in : ; , ,ti

Water-Cooiinc] M,-imioid

•earn Lit op

Isotope ProductionTargets

Beam DegraderProton-Irradiation Experiments

Vacuum-to-Air Window

1 m

Fic_ji. !Pt J' . i.tir^.i i r i , ou i o i Tarqpto td t -on A 6 f'Jote the relat ion a m o n q t r e p i o t o n mad ia t ion

s > [ t < :•;,'• •• ». •., ...rv i ,,i-,;r.iiY, ,-ind tl .o irv.ti .Men ta t i on raC^S

27^


Measurements of PowerDeposition at the LAMPFNeutron Radiation EffectsFacility

H L) BrOu\n 10b)

As part of the effort to characterizethe LAMPF neutron Radiation F.ffectsFacility1 ( REt'), measurements havebeen made ot the power depositionin a copper calorimeter located in thespallation neutron flux about 20 cmbeneath the isotope productionstringers. Calculations'2 of the neu-tron flux showed that the flux shouldbe peaked near this location and thatthe heat flux should therefore be at amaximum here.

A calorimeter was constructed oftwo copper cylinders with electricalheaters on the inside and outsidecylinders. The heaters allowed us tosupply measured power levels to thecalorimeter and thereby to calibrateit. The temperatures in the calorime-ter were modeled using a time-de-pendent equation. To determine the

power deposition, we needed toknow the emissiviry of the innercylinder, the heat-transfer coefficientbetween the cylinders, and thethermal mass of the inner cylinder.All these coefficients were de-termined from the initial calibrationruns, The calorimeter was insertedinto REF stringer 3 and irradiated for2 days. Temperatures were recordedusing thermocouples attached to anautomated data-collection system,and the beam current was monitoredusing graphs of the beam current ob-tained from the central control room.Analysis of the data showed that thepower density plotted versus timewas approximately a constant, equalto aDout 2 W/cmVmA.

The power deposition, which hasbeen measured at one position at theREF, is in reasonable agreement withcalculated values. Further measure-ments are needed to determine thevariation in power deposition withposition along the beam line andwith radial distance from the beamline.

References

1. D. R. Davidson, L. R. Greenwood, R. C. Reedy, and W. F. Sommer,"Measured Radiation Environment at the LAMPF Irradiation Facility," 12thInternational Symposium on Effects of Radiation on Materials,Williamsburg, Virginia, June 18-20, 1984, Los Alamos National Laboratorydocument LAUR-84-1050 (June 1984).

2. D. R. Davidson, W. F. Sornmer, J. N. Bradbury, R. E. Prael, and R. C. Little,"Characterization of the LAMPF Beam Stop Area Radiation Environment,"Los Alamos National Laboratory document LA UR 83 33 (January 1983).


800-MeV Proton Irradiation ofMaterials for the SIN Beam Stop

if V.

SIN has been studying the possibility of constructing a neutronsource/beam stop that uses a verticalcylinder of liquid lead bismuth. Atthe design current, the proton beamcurrent density will be about2i> uA/cnr, essentially the same asthat now available (at HIM) MeY ) atthe LAMPF A•(> radiation effects area.The window in the cylinder basemust be made ot an alloy that ischemically compatible with themolten, lead hiMViuih and that can

maintain reasonable ductility andstrength following proton irradiationtofluenc.es of about K)21 p /enra tatemperature of about HOO'C. Initialexamination ol materials for chemi-cal compatibility with the leadbismuth indicated that iron based alloys and tantalum could both be candidates. Materials selected for irradiation included l;e, Fe 2.25Cr IMo,Fe-12Cr-lMo;HT-9),andTa.

Tensile samples were heat treatedand encapsulated in a lead bismutheutectic alloy, sealed in an outer steelcapsule and proton irradiated. A setof high-fluence samples receivedabout 5.4 X l(li(l p/cm2; a set of low -fluence samples, about -!.H X1019 p/cm2. In pure iron, these results

inUJor

200

150

100

50

0C

i i

.,— HIGH FLUENCEa

I LOW FLUENCE

UN-IRRADIATED

Ki i

) 5 10

1

,—-—

1

15

ENGINEERING

_—-

IRON

STRAIN

I

^—

I

20

(%)

l

-

. — -^ -

25 50

HG'Jhr •'i ess - strain curves tor non as a lunction ot proton Muence

275


R a d i a t i o n I « < - ' : • , ,

correspond to aboui 1.6 and O.l-i clpa,respectively.* Hxamination ot thesamples following removal from theircapsules showed no corrosioncaused by contact with the moltenlead bismuth. The samples were thendipped in acid to remove alpha conlamination and tensile tested in thehot cells (at another site in the Labo-ratory) at a strain rate of 9 X I()~Vs.

The yield and ultimate strengthsincreased in all materials followingirradiation, whereas the ductility, as

measured by the uniform plasticstrain, generally decreased. Figure 1shows stress-strain curves for iron as afunction of fluence. The pure metals,iron and tantalum, exhibited thegreatest radiation hardening and emhrittlement; the HT 9 alloy showedthe smallest changes in strength andductility. Additional work is underway to study the radiation modifiedniicrostructures using transmissionelectron microscopy.

"Reference 1 andiMlurnviliuipiii.Klt'ilt.tYl> K 1 laLos Alamos National! aboialor, .luii! hiHh

Reference

1. C. A. Coulter, D. M. Parkin, and W. V. Green, "Calculation of RadiationDamage Effects of 800-MeV Protons in a 'Thin' Copper Target," Journal ofNuclear Materials 67, 140 (1977).

276


VAX Cluster

Computing capacity at the DataAnaUsis Center ( DAC ) was significaniK enhanced during l98Swiththe .uklnii MI tit .1 VAX H(ii)l), a newmachine equivalent in approximatelyfour VAX I 1/ "'SO computers. One olthe l)AC VAX 1 1/-Si)s was Hanst'erred li > the Central Control RoomI Cl.K ) in -.uppori ihe operations programmmg section, leaving ihe DACwith .i cluster ol ihree VAX 1 l/"HOsaiul a VAX 8(>nu.

flu- \ AX Sod'i considerably increased the computing capacity atihe DAC, and that capacity was usedalmost instantly (see Fig. 1 ). TheVAX 8W)0 also increased disk space,both tor scratch space ( 1.-» Gbyte)and lor system storage, because theVAX Khun uses a separate system disktor optimum operation. In addition,one 11 ^S tape unit Ui2S(i/l(>(l(i bpi)was upgraded lo a TA~"H and is controlled through the HSCSO clustercontroller; this means that the tapeunit is available to any machine in ihvcluster, not simply to a specific ma-dune. Another Tl'"H tape unit waspurchased in 1985 and slaved to theTA"8 so that it is also available to thecluster.

Other Support

The tape library at the DAC wasexpanded in 19HS, from a capacity ofabout "'000 to about 12 SOD tapes. Thetape library racks are currently about

Data-Analysis Center

! ' • ' ! - •

Several Digital Hquipmeni Corporation ( DL'C ) LN'H desk top laserprinters were purchased during 19HS.Some units are supported Iromprinter ports off specific terminalsand some are set up as spooled devices in the OAC and in the Laboraton'Office Building. Support isprovided lor word processing,including Greek and mathematicalcharacters.

Some effort was expended evaluat-ing a terminal replacement for theoutdated VT64O terminals now in usearound LAMPF. The new terminal requirements included higher-resolu-tion graphics and compatibility withthe DEC terminal VT100 style keypad(a favorite for use with the DEC EDTeditor). Specifications are beingprepared to send to various vendorsfor bids. Note that the hardcopy units(Tektronix -1612) will not be able tosupport higher-resolution terminals.

277


Networking

The LAMl'l' local area networkcable currently runs from the DAC toAreas B and C, throughout Area A,and to the new neutrino experimentat the far east end of the accelerator.The total length of the coaxial cablecomprising the network is ""(H m.Currently III nodes are connected,with capability for growth to 2(>u toM)D nodes The I'lthemet network hasproved to be a highly reliable andcost effective means lor inlormationexchange.

With the advent of the network,experimenters are now better able tomake efficient use of the iesources at'he DAC and throughout the experimental areas. This network, cou-pled with the connection over theLaboratory broadband network to theC Division computers and throughthose computers to worldwidenetworks such as Telenet andArpanet gKes I.AMPF experimentersalmost direct access lo home institulions and other collaborators.

VAX CPU Usage at MP Division

6 -

1978 1979 1980 1981 1982 1983 1984 198b 1986 1987

it At-;

1"' J ' '

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. i l i ' i r , M I | l , i

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FACILITY DEVELOPMENT.".r.il i

LAMPF Control System

The C e n t r a l l . o i i t ro l Km mi ( C C K I

VAX c o m p u t e r o n it ni l s y s t e m 1 w a s

u s e d ' ' T I ii I U i i 1 \11| 11 i f n e w I I i i i j c i

to r a m i t r a n s pi <n I I I H ^ d u r i n g t l i e

s p r i n g 1'JHS , i a e l e iu l i >r s t a r t u p A p

p l i c a t i o n s p r o g r a m c o n v e r s i o n In MM

t h e S l i L S i n I , i l l u - \ A X 1 ! " " H i I i s

l a r g e l y i 1 • i I i ( i l e t e \ M ' I ' I U K I V A X i s

U s e d i n t h e i i K ti T s \ s l e i n d e \ e l i > p

n i e i u , a m i i I n s u r i n g i 'I i h e t w o

V A X e s i-, u i i d i - i v \ a \ Yv h e n L A M I ' I

b e a m i s 11 I I i . f > I > H I I I I I I i e l a t e s p r i n g

i l l I ' J M d . w e vv i l l b e u s i n g t h e n e w

a m i r . > l s \ s i e i n s i i i i w a r e e x e I n s i \ e l y

The SI'.I. H in w ill p r o b a b l y r e m a i n

t h r o u g h tha i o p e r a t i n g c y c l e as a s e

c u r i n b l a n k e t • ir In c o v e r t h e e ha n e e

tha t a pi t igra in h a s b e e n < Miiit ted. l;t il

l o w i n g t h i s c \ c l c . t h e Si. 1. S i u w i l l b e

r e m o v e d . \X u h t h e \ Hal w o r k d o n e ,

e s s e n t i a l i m p r o v e m e n t s a n d I in l i re

g r o w t h e a n b e ei u i s i d e r e d

Software Optimization Issues

Once an applications program iscomplete, we evaluate its responsiveness. Hi, is too slow, several tools areused to determine where it is spending its time We t'iiul that most programs spend the majority ol theirtime in \er\ limited areas of tlie code.These areas are then made more eHicient In soiiu-1 .ises these areas are insubroutines that are used on a systern wide basis, such as those supporting plotting anil data taking, andattacking these melliciencies therelore increases responsiveness on asystem wide basis.

Several graphics applicationsproved to be quite slow We wereusing a set of routines supplied and

supported by the Laboratory Compiiting Division. We discovered lhai theyhad taken one high level set olroutines, the package supported bythe National Center lor AtmosphericResearch ( NCAK ), and laid it on topol the set of routines C 1 )ivision liassupported for years iCdM. By IVMK >«•mg this bottom layer, we doubled I In-put t ing speed while keeping thestandard NCAK interlace.

We also found that programs thatacquire accelerator data spe i Hi in iretune than expected managing spacelor global data structures Hvpreallocating memory lor some olthese structures, " e reduced dataacquisition CPU usage by a factor of 1without sacrificing the diagnosticcapabili'ies afforded by theseglobally accessible sirm. Hires. Because data taking routines are part ofthe control system run lime library,optimizations in this area providedimprovements in most ol the applications programs.

Several applications programs acquire data from a large number ofaccelerator devices on a repetitivebasis. Programs that support monitoring, as well as the program that displays the status of the system andaccelerator operational status, are examplts. The latter program, for instance, acquires data Iron; appro.ximately 301) different devices onceevery 3 s. Mecause applications programs must use symbolic devicenames for data acquisition, they areunable to make direct use ol thehardware organization to optimizetheir data access. We provided a dataacquisition routine that allows an ;inplication to combine a group ol disparate devices into an aggregate tie

LAMPF Computer-Control System

!• |H

279


vice. Reading the' aggregate device,the data-acquisition routines acquiredata for each component device,thereby minimizing the number ofhardware references required. Thisoptimization lias decreased the tl 1*1'time needed for the rt status programby a factor of 3 while retaining thehardware independence afforded b\symbolic device naming. ( More details on data-acquisition opiimi \itions can be found in Kef. 1.)

Another interesting optimizationalso involves this status program.During production, the operatorsoften run the program from severaldifferent consoles, which initiallymeant running a separate copy of theprogram at each console, substan-tially loading the system resources.Now, additional requests for thestatus display are met by a slavedcopy at negligible cost.

VMS Environment

Some of the jobs done by operations personnel are more efficientlyimplemented by the VAX/VMS operating system than by the control sys-tem. By using a VMS interface forthese tasks, we do not need specialapplications programs. Examples ofthese tasks include displaying VMSand accelerator status information,displaying file directories, updatingapplications-program data files, andgenerating reports from the ac-celerator device description database.

However, if operators are loggedin as normal users, accidental filedeletions are possible. To preventthis, VMS access is limited by an indirect command file thai is activatedwhen an operator logs in on a touchpanel. The command file allows theoperator to execute a small subset ofVMS commands, and the only way toleave the indirect command procedure is by logging out. Thissimplifies and protects the operatorinteraction.

Remote Computer Network

Five small PDP 1 1 computers arelocated throughout the facility (AreasA and B, the switchyard, transitionregion, and the ion source test stand)for remote data acquisition and control through CAMAC data linksdirected by a communications nodecomputer (NET 11) in the CCR. Sev-eral other small PDPs are also inplace for special tasks. This networkwas built up over the years largelywith customized hardware and soft-ware, leading to problems with main-tenance and development.

The planned upgrade will replacethe PDP-1 Is with micro-VAXes andthe network with Ethernet. Ethernetwill allow straightforward networkexpansion and can be driven by theCCR VAXes without the NET-11 relaynode. Four of the data-acquisitionmicro-VAXes will not have disks. Wewill probably install the VAXELNmemory-resident operating system,which can be down-loaded from the

280


CCK over Fthernet. VAX1-.LN is willten in and supports FPASCAL, an Intenuuional Mandards iirgani/ationPASCAL wuh extensions tor real limeprocessing

Programs running on the microVAXes will access daia through symbolic device names, as is currentlydone by die VAX 1 1 . ~K0 programsThe device description daia bast' willhe maintained on the VAX II "S IK.nid down loaded as needed by theremote computers.

At cess between computers will hesupported through a paradigm lorcalling procedures for remote computers. The computer at the ionsource test stand (1STS ) is an exceplion in that it is essentially a standalone system with no direct connec(inn to the accelerator. We are considering adding local disk storage tothe ISTS micro VAX and running themicro VMS operating system. We expect that portions of the VAX-1 l/~H()control system can he used to handlethe ISTS environment. The Fthernetconnection will be used to transfersoftware and data bases.

At die present time the F.themetcable has been purchased and is inplace. Micro VAXes have beenpurchased tor the switchyard, themaster timer, ami the isTs computers. but are not yet installed.

Sum man

The upgrade from the sFL N-i(> tothe VAX 1 1 "Sli is all but completeMost of the applications programsoftware is now in production. Thissoftware has been monitored to tincover response bottlenecks. Someoptimizations have been im-plemented with good results. We intend to continue to monitor performance and make additional changeswhere they make sense. We havebeen able to provide a limited VMSenvironment for the operators so thatthose tasks most easily accomplishedby using VMS can be done safely.Finally, the control system networkupgrade is well under way. We project that this task will be completedin about one more vear.

References

1. 0 F. Schultx. and S. K. Brown. "On-Line Replacement of a ParticleAccelerator Control Computer," IEEE Real-Time Systems Symposium,Miami Beach, Florida. December H 10, 19K1, IFF.E CatalogNo. «lCHl~t)()-i, pp. "H-H2.

2. S. C. Schaller, J. K. Corley. and P. A. Pose, "Optimizing Data Access in theLAMPF Control System" (to he published in IEEE Transactions on Nu-clear Science ).

281

ACCELERATOR OPERATIONS

Accelerator Operations This ivpi >ri L'I >vcrs opera t ing cyi ies

l 1. l3. and i i Tlii' accelerator was in

operat ion Iroin April 11 th rough I >e

i c m b c r 11, ll;NS. Beams were

provided lor research use lor

IS" days, and t'i ir facility deve lop

nu'iu tor JS days, .\lnuvst all the la

cilily d e v e l o p m e n t l ime was usi 'd t«>r

I'roion Storage King (I'SK ) i0111

missioning. A suininary ol in lonna

tion on b e a m s pro \ ided lor ivsoari'li

is given in Tab le I

Anew high in iens i r . 11 ion soiirct

was brought inio i iperai ion lo

provide beam for ihe I'SK With die

except ion ol t h r e e shifts for a nucleai

chemistry e x p e r i m e n t , beam trom

the new source was used exclusively

lor operaiinii and deve lopmen t in tin

I'SK and Line 1-. Peak II" beam cur

rents in excess o lO inA and average

beam currenls as h igh as y-, (,iA were

del ivered to the I'SK. il~ beam avail

ability was " , US, and ~'i)'\, lor cycles

•il, -t.V anil i i , respect ivi ly.

Bean"' b'at is! cs 'or L •,ci

H+

p-

scheduieci berti ' i ih iscnedu led beam ih)

oeaTi a.anabi11, ( > )t e a m a-.aii3Diii!>, i >)

average ct.rren' (jiA)averaqeci nen; (nA)3

beam duty tactc ( t )beam duty lacto-' (*)

aAveraged ever entire cycle

4? Tnrougn 44

C vrlp 4?

30

15991911

66

"0010

6-93 9

Cycle 4 3

38

1 3661 338

897 i

8306

6 93 9

Cvcle44

41

15041491

CD O

00 CO

90022

6-93-9

284

ACCELEHATOR OPERATIONS

T h e II i\\ a \ a i l a b i l i l \ • n l I1 b e a m s

d u r i n g a i l t ' v i i a n d -i.S w a s d i r e c t l y

r e I . i k ' i I i i i | H I i h I f i n - i w i t h ilit* ii. >t i

si H I i i e A i'11;111j^t* i n s o u r c e o j H ' r a t i n g

p a r a m e t e r s d u r i n g t h e l a t t e r p a r t i it

v \ e l f i i r e s u l t e d in a ML;1111ieant m i

provi"men! in Mahililv and a t ive to ld

increase n\ 1' b e a m c u u e t u

Acce I e nil or o p e r a t i o n was s n n x u h

and re l i ab le , ea.sily p rov id ing 11"1

beam in t ens i t i e s ol 1 inA at lJ"i. i lmy

iaclov a n d l)-io )j,A.;ll <>"•„. l 'oor l\ +

a\a i labi l i t \ d u n n i ; cycle i J w a s

largely due tn lailuri" i >l a (|iiadrupnle

triplet in an A 1 target cell; ground

taults and a resuliant lar^e water leak

rec|uired replacement ol'cuiilam

lines and '.nst over a week nl un

schediileil downtime.

A summary of unscheduled facility

downtime during research shilir. is

given in Table II. Because some ot

the outages are com urrent, and be

cause some attected only one ot three

beams, the h»al is much greater than

tile beam downtime.

:AtsLE=: .. inscheOuWM^hmcL^nn

f-ategor-,

I'D1 MK- .•iP'pliiiMrj.incitiansmpiSiOnlme5(VN MH_- in\-liiiei S\ Sib-UK./acujmsvstemsMagnetsMagnet power suppliesinterlock ssstems'.on sources ar'«.1 ("or^cicfl-'vVa'.lon high vCooling vvater sv stemsComputer contmi and data acquistionProduction targetsPuise timing systemsMisceitane<"ii i^ (utilities, ligi nhing, etc ;

rOTAL

me riunng Shifts in 1985

Downtime

2559070

2236529

oltage supplies 79833223019

118

1802

Per Cent of Total

1454

124cL

4421417

285

Milestones

MILESTONES

MILESTONES 1968Official Ground Breaking February 15, 1%HSpinoff-. Adoption of LAM1JF Accelerating Structure

tor X Ray Therapy and Radiography Machines ca 1%H

1970

5-MeV Beam Achieved June 10, 1970Adoption of a LAM PF Standard Data-Acquisiiion

System August 1970

1971100-MeV Beam Achieved211-MeV Beam Achieved

1972

June 21, 1971August 27, 1971

June 9, 1972800-MeV Beam AchievedSpinoff: First Use of Electrosurgical Forceps in

Open-Heart Surgery (University of New Mexico) September 13, 1972Discovery of 236Th (Experiment Zero)Dedication to Senator Clinton P. AndersonSpinoff: First Hyperthermic Treatment of

Animal Tumors

1973First H Injector BeamFirst Simultaneous H+ and H~ BeamsBeam to Area BFirst Experiment (#56) Received BeamFirst Meson Production, Beam to Area A

1974

Beam to Area A-EastFirst Medical Radioisotope ShipmentUsable 100-|iA Beam to SwitchyardPi-Mesic Atoms with "Ticklish" NucleiFirst Experimental Pion RadiotherapyFirst Tritium Experiment (80 000 Ci)Start of Great Shutdown

September 25,1972September 29,1972

October 1972

March 28, 1973May 4,1973July 15,1973August 24, 1973August 26, 1973

February 6,1974July 30, 1974September 5,1974October 13,1974October 21,1974November 1974December 24,1974

288

MILESTONES

1975

New Precise Measurements of Muonium HyperfineStructure Interval and ji+ Magnetic Moment 19~'5-~'"'-H()

Q Data Acquisition Software Operational June 197SSpinoff: First Use of K"Rb for Myocardial Imaging

in 11unians ( Donner Lah, Lawrence BerkeleyNational Laboratory) June 1975

Spinoff: First Flyperthermic Treatment ofHLiman Cancer ( L'niversity ot New Mexico) July 11, 19?5

Accelerator Turnon August 1, 19"?5Acceptable Simultaneous 100 u.A H+ and 3 |iA H~

Beams to Swiichyurd September 1-i, 1975Production Beam to Area B October"7, 19*75)

1976

First Pions Through EPICSProduction Beam in Areas A and A-East:

End of Great ShutdownMuon-Spin Rotation ProgramSpinoff: First Hyperthermic Treatment of

Cancer Eye in Cattle (Jicarilla Reservation)100-uA Production Beam in Area AExperiment in Atomic Physics ( H~+ laser beam):

Observation of Feshbach and Shape Resonancesin FT

Double Charge Exchange in l6O: LF.P ChannelStartup of Isotope Production FacilityHRS Operation BeginsMaintenance by "Monitor" System of

Remote Handling

1977

March 18,1976

April5,1976June 1976

June 3,1976August 1976

October 1976Octobers, 1976October 15,1976November 1976

Fall 1976

Proton Beam to WNR March 12,1977Polarized Proton Beam Available April 1977Spinoff: First Practical-Applications Patent Licensed

to Private Industry April 12,1977Pion Radiotherapy with Curative Intent May 1977Proton Computed Tomography Program June 1977Experimental Results at Neutrino Facility July 1977Cloud and Surface Muon Beams: SMC July 1977EPICS Operation Begins August 1977300-uA Production Beam in Area A Fall 1977

289

MILESTONES

1978

AT Division Established7tu Spectrometer Begins OperationOperation of Polarized-Proton TargetSuccessful Water Cooled Graphite Production

Target

1979

Spinoff: First Thermal Modification ofHuman Cornea (University ot Oklahoma)

6()(.)-nA Production Beam in Area ANew Limit on u —* ey

1980

January 1, 1978February 1978Spring 1978

November 1978

July 11, 1979November '979December 1979

Experimental Measurement of the Strong-InteractionShift in the 2p-Is Transition for Pionic Hydrogen

Commercial Production of RadioisotopesSpin Precessor Begins OperationData-Analysis Center OperationalVariable-Energy OperationSingle-Isobaric-Analog States in Heavy NucleiSpinoff: First Use of 82Rb for Brain Tumor Imaging

in Humans (Donner Lab, Lawrence BerkeleyLaboratory)

Production of Fast Muonium in VacuumDouble-Isobaric-Analog States in Heavy NucleiFocal-Plane Polarimeter Operational at HRSSafety Award to LAMPF Users Group, Inc. for

Working One Million Man-Hours Since 1975Without a Disabling Injury

New Measurement of Pion Beta Decay—ImprovedTest of Conserved-Vector Current

1981

First Excitation of Giant Dipole Resonance byPion Single Charge Exchange

First Excitation of Isovector Monopole Resonancein 120Sn and 90Zr by Pion Single Charge Exchange

Search for Critical Opalescence in 4nCa

1980-81-82January 1980February 1980April 1980June 1980June 1980

September 1980Fall 1980October 1980October 1980

October 27, 1980

November 1980

March 1981

March 1981September 1981

290

MILESTONES

1982

Average Beam Current of LAMPF Accelerator

Staging Area ConstructedParticle Separator Installed at SMC"Dial a Spin" Capability on Line B Permits Different

Spin Orientations for MRS, Line B, and F.PBsimultaneously

Time Projection Clumber in Operationimproved Test ot Time-Reversal Invariance in

Strong InteractionsSearch for Parity Nonconservation in [>f> Scatteringdt Fusion Catalyzed by Muons

1983

LAM PI" Accelerator Produce.1. Proton Beamof 1.2 mA

First Observation of v,-c~ ScatteringResult tor Asymmetry in {>[> Scattering Caused by

Parity Violation: .-I,. = I 2,i ± 1.1 ) X \{V"at Ml Mi MeV

19821982

19H2198.*

January 1982November 1982November 1982

February"7, 1983October 1983

November 1983

1984

Duty Factor >9";> AchievedTotal Cross Section for v,,-tj~ Scattering:

aT= 1 ()"•'"' £v(GeV) curClamshell Spectrometer On LineHigh Intensity H~ Source OperationalBranching Ratio for(i+— c+e+c~ Probes Mass

Range to lOTeV

February 1984

May 1984June 1984September 1984

October 1984

291

MILESTONES

1985New Beam Stop Installed by Remote-Handling

SystemHigh-Intensity H~ Injector OperationalNew Switchyard Permits Three-Beam OperationProton Beam to Proton Storage Ring (PSR)Routine Production at Beam Current of 1 mAiTp — n°n Reaction Observedrj-Meson Production Near Threshold17-mA Peak Current AchievedTime-of-Flight Isochronous Spectrometer

(TOFI)OnLineTest of the Relativistic Doppler Effect at 0.84 c by

Collision of an Atomic Beam with Laser Light

Spring 1985April 1985April 1985May 1985Summer 1985July 1985August 1985September 1985

November 1985

1985

292

Appendixes

APPENDIX AOp--.

APPENDIX A:Experiments Run In 1985 No. Channel

BeamHours Experiment Title

225 NEUTRINO-A

267 ISORAD

294

455

533

572

AB-NUCCHEM

P3

HRS

EPICS

588 EPB

589 BR

601 EPICS

623 HRS

639 SMC

657 EPICS

3653 A Sudy of Neutrino ElectronElastic Scattering

3628 Preparation of Radioisotopes ForMedicine and The Physical ServicesUsing The LAMPF Isotope ProductionFacility

18 High Energy Nuclear Reactions

774 High Precision Study of The y=

Decay Spectrum

126 The Asymmetry in The (P,n)Reaction on 6Li at 800 MeV

200 A-Dependence of The (n+,nT)Reaction and The Width of a DoubleIsobaric Analog State in HeavyNuclei

321 A Search For Long-Lived States ofThe H" Ion

343 Free Forward NP Elastic ScatteringAnalyzing Power Measurements at 800MeV

246 Determination of Isoscalar andIsovector Transition Rates For LowLying Collective States in 90Zr and2OBpjj B y n+ an(j n- inelasticScattering

152 Measurement of Cross Section,Analyzing Power and DepolarizationParameters in The 28Si(p,p')28Si(6- T = 0 AND T = 1) Reactionat 400 MeV

177 Muon Spin Rotation Study of MuonBonding and Motion in SelectMagnetic Oxides

189 Inelastic n~ Scattering FromThe N = 26 Isotones

296

APPENDIX Al'j Run in 19B!j

BeamNo. Channel Hours Experiment Title

665 BR 418 The Measurement of The InitialState Spin Correlation ParametersC n AND Cc, In N-P ScatteringAT 500, 650, and 800 MeV

687 HRS 96 Measurement of The Spin RotationParameters In 208Pb and In 40Ca at400 Hev

705 P3 568 Study of Pion Absroption In 3He onand Above The (3,3) Resonance*

722 HRS 96 Measurement of Cross Sections andAnalyzing Powers for Elastic andInelastic Scattering of 400 to 500MeV Protons From 14C

723 EPICS 199 Measurement of The Neutron andProton Contributions to ExcitedState in 39K By n+ and n~Inelastic Scattering

726 SMC 570 Search for The C-Noninvarient Decay

727 SMC 252 Measurement of The Efficiency ofMuon Catalysis in Deuterium-TritiumMixtures at High Densities

258 Search for The Negative Muonium Ion

958 Tuneup of The Time-of-FlightSpectrometer For Direct Atomic MassMeasurements

3173 Proton Irradiation Effects onCandidate Materials For The GermanSpallation Neutron Source (SNQ)

770 BR 1953 The Measurement of NP ElasticScattering Spin CorrelationParameters With L- and S-TypePolarized Beam and Target Between500 and 800 MeV

742

752

769

SMC

TTA

RADAMAGE-1

297

APPENDIX AExperiments Run in 1985

No. ChannelBeamHours Experiment Title

773 EPICS

799 HRS

800 EPICS

807 P3

811 LEP

813 LEP

814 LEP

815 EPB

827 P3

828 LEP

832 EPB

833 EPICS

286 Measurements of (Jl+,Jl ) AngularDistributions on 56Fe at 164and 292 MeV

120 Large Momentum Transfer Measurementsof Ay for 800 MeV P +

208PbElastic Scattering

277 Inelastic Pion Scattering From

344 Test of The LAMPF RecoilPolarimeter (JANUS) in Measurementsof The n~ P Elastic ScatteringProton Polarization at 625 MeV/C

248 Study of Unnatural Parity States inNuclei Using Low-Energy Pions

131 Pion Charge Asymmetries for 13Cat Low-Beam Energies on The LEPSpectrometer

155 n* Nuclear Elastic ScatteringFrom Ni and Sn Isotopes atEnergies Between 30 and 80 MeV

1256 Measurements of AMQ, S<A,, in p*p* -» Pnn+ at 50t650, 720, and 800 MeV

andi, 580

383 Study of Isobaric Analog States inPion Single Charge ExchangeReactions in The 300- to 500-MeVRegion

258 Total and Differential CrossSections for n+ d -* ppBelow 20 MeV

588 Gamma Ray Angular Correlation for12C(P,P')12C(15.11)

250 Continuation of The Investigationof Large-Angle Pion-NucleusScattering

298

APPENDIX k

Experiments Run in 1985

No. ChannelBeamHours Experiment T i t l e

836 EPICS

837 HRS

841 EPICS

£42 HRS

848 LEP

851 HRS

852 P3

853 HRS

854 SMC

855 HRS

856 P3

859 P3

209 Energy Dependence of PionScattering to The Giant ResonanceRegion of 20BPb

127 Measurement of Spin-Flip CrossSections Up to 40 MeV Excitation in58Ni and 90Zr

171 Forward-Angle Pion InelasticScattering on Light Nuclei

488 "uSR Shift and Relaxation Measurementsin Itinerant Magnets"

69 In-Flight Absorption of Low EnergyNegative Pions

388 Search for Recoil Free A Productionand High Spin States in the208PB(p,t)205PB Reaction atEp = 400 MeV

700 Measurement:: of (rt~,n) Reactionson Nuclear Targets to Study TheProduction and Interaction off| Mesons With Nuclei

214 Measurement of WolfensteinParameter at 650 MeV and dE/dSat 500, 650, and 800 MeV forpd -* pd Elastic Scattering

177 Muon Spin RsearchH in Oxide SpinGlasses

151 Measurement of 2°6pb-208Pb GroundState Neutron Density Difference

140 Comparison of Double ChargeExchange and Inclusive Scatteringin 3He

170 Study of The A Dependence ofInclusive PionDouble-Charge-Exchange in Nuclei

299

APPENDIX A

BeamNo. Channel Hours Experiment Title

860 LEP 256 Inelastic n* Scattering toExcited 0+ States at EnergiesBetween 30 and 80 MeV

866 EPB 278 Neutrino Source Calibration

869 SMC 145 Higher Precision Measurement of theLamb Shift in Muonium

877 SMC 113 The Microdosimetry of ErrorInduction in Microelectronics

879 HRS 184 Characteristic Dirac Signature inLarge-Angle t + 40Ca ElasticScattering at 500 MeV

882 LEP 855 Measurement of the DifferentialCross Section for n~p -» n°nat10, 20 and 40 MeV

883 HRS 177 A Study of the Reaction Mechanismfor the 2H(i?,Y)

3HeReaction at 800 MeV

884 LEP 415 Pion Double Charge Exchange onH C at Low Energies

885 HRS 157 Measurement of KgS for theI>p -> dn+ Reaction at 650and 800 MeV

888 SMC 494 Study of the Decays Ji+ -»e+vgY and Jl

+ -> e+e+e~Me

891 HRS 150 Development of Zero CagreeSpin-Flip Measurements at HRS

896 HRS 231 A Test of the Dirac Treatment ofProton-Nucleus Inelastic Scattering

897 LEP 52 Pion Single Charge Exchange in7 Li to the Isobaric Analog GroundState of 7Be

300

APPENDIX A

C | . n n ; r i l ' , I I ' I . M i l l 1 9 8 r i

No. ChannelBeamHours Exoeriment Title

898 EPICS

899 LEP

902 HRS

903 HRS

905 EPICS

906 EPICS

907 HRS

908 EPICS

914 SMC

917 P3

927 LEP

928 EPB

102 Pion Elastic Scattering from 4He- A Test of Charge Symmetry

60 A Measurement of the NeutronDeformation of 165Ho by PionSingle Charge Exchange

72 Inelastic Scattering*of 500 MeVPolarized Protons from 88Sr:Determination of Neutron TransitionDensities

64 A Study of Transition Nuclei in theRare Earth Region by ProtonInelastic Scattering

329 Elastic and Inelastic Scattering ofIT* on 3H and 3He to TestCharge Symmetry, Compare FormFactors, and Investigate theReaction Mechanism

240 DCX on 44Ca

241 Spin Excitations in 40Ca and48Ca

114 Angular Distribution for the42Ca(ji+,iT)42Ti(g.s.)Reaction at 290 MeV

137 Measurement of the Analyzing Powerof a Muon Polarimeter for Use in aSearch for Muon Polarization in theDecay K-i UP

70 Pion Charge Exchange to Delta-HoleStates of Complex Nuclei

106 Investigation of Non-Analog DoubleCharge Exchange Between 50 MeV and120 MeV

490 p* + n quasielastic Scatteringfrom Deuterium

301

APPENDIX A

no. ChannelBeamHours Experiment Title

933 LEP 158 Study of the Mass and EnergyDependence of Ultra Low Energy PionSingle Charge Exchange

936 RADAMAGE-1 2053

RADAMGE-1 2053

Dosimetry Experiment toCharacterize the RadiationEnvironment at LAMPF Target StationA-6Dosimetry Experiment toCharacterize the RadiationEnvironment at LAMPF Target StationA-6

941 SMC 149 Muon Spin;Relaxation Studies ofDisordered Spin Systems

942 LEP 69 Measurement of Low Energy CrossSections for the12C(n±

fnN)11C Reactions

944 SMC 384 Feasibility Study for an Experimentto Search for Muonium &Antimuonium Conversion

945 EPICS 100 DCX on Nickel

947 EPICS 100 Measurements of Large-AnglePion-Deuteron Scattering

950 EPICS 200 Mass of the Extremely Neutron Rich48Ar

957 P3 204 "Inclusive PionDouble-Charge-Exchange in Lightp-Shell Nuclei,"

963 SMC 280 "Experimental Investigation of MuonCatalysis,"

979 LEP 169 "A Search for T=2 DibaryonProduction in the d(n+,jT)XReaction,"

302

APPENDIX B

New Proposals During 1985

No.

954

955

956

957

Spokesperson TitleAPPENDIX B:New Proposals During 1985

958

959

960

R.J.Univ.

G.U.Univ

J.J.Los iM.L.UnivR.L.Univ

A.UnivJ.J.Univ

G.A.UnivJ.L.MITP.A.Los

Peterson. of Colorado

Hoffmann. of Texas,Austin

JarmerMamosBarlett

. of Texas,AustinRay

. of Texas,Austin

Saha. of VirginiaKelly

. of Maryland

Rebka, Jr.. of WyomingMatthews

M.GramAlamos

"Isospin Amplitudes For GiantResoneinces In 5 8Ni and 6 4Ni,"

"Search for Experimental Proof ofthe Existence of Lower Componentsin the Nuclear Wave Function,"

"Microscopic Structure of theCalcium Isotopes,"

"Inclusive Pion Double-Charge-Exchangein Light p-Shell Nuclei,"

G.W. Hoffmann "Study of the 90Zr(p,i?)90Nb -Univ. of Texas,Austin (IAS) Charge-Exchange Reaction'at

500 MeV,"J.B. McClellandLos Alamos

C.F.Univ.H.T.Univ.S.Univ.

Mooreof Texas,AustinFortuneof PennsylvaniaMordechaiof Texas,Austin

"Inelastic Pion Scattering from2 0Ne,"

G.R. BurlesonNew Mexico State Univ.

K.F. JohnsonArgonne Nat. Lab.L.C. NorthcliffeTexas A&M

"Measurement of and Acr,pin Free Neutron-Proton ScatteringBetween 300 and 800 MeV,"

M)1,

APPENDIX BNew Proposals Dunno ll-)8b

No. Spokesperson Title

961 L.C. Northcliffe "Measurement of theTexas A&M Spin-Correlation Parameter

ANN(9) for n-p ElasticScattering at 800 MeV,"

962 S.J. Seestrom-Morris "Target Mass Dependence of theUniv. of Minnesota Isovector Contribution to the

Giant Quadrupole Resonance,"

963 A.N. Anderson "Experimental Investigation ofMuon Catalysis,"

964 G.S. Blanpied "Study of (n ,p), and (n+,p)Reactions with EPICS,"

A.N.EG&G,M.

AndersonIdahoLeon

Los AlamosS.E.BYU

G.S.Univ.

Jones

Blanpiedof South

CarolinaJ.-P.SWISS

E.L.Univ.

EggerINST

Chuppof New

HampshireP.P.Univ.

B.G.ASU

Dunphyof New Hampshire

Ritchie

965 E.L. Chupp "Test and Calibration of Detectorfor Solar Neutrons and Gamma Rays,"

966 B.G. Ritchie "Pion Absorption on Quasideuteronsin 10B (n-1

967 D.R. Tieger "Inclusive n' Scattering at 100Univ. of Washington MeV on C, Ca, Sn, and Pb,"I. HalpernUniv. of Washington

968 F. Irom "i-jtudy of Inelastic Scattering ofLos Alamos rt~ from 7Li and 14C at Low

Energies,"R.J. PetersonUniv. of Colorado

969 M.D. Cooper "MEGA - Search for the Rare DecayLos Alamos u + -» e+y,"

304

APPENDIX B

New Proposals During 1985


970 C.F. MooreUniv. of Texas,AustinC.L. MorrisLos AlamosR.J. PetersonUniv. of Colorado

"Measurement of the Delta-NucleusInteraction by Pion InelasticScattering to the 1+ Doublet in

971 R.W. FergersonRutgers Univ.

"Measurement of the Spin-RotationParameter Q for the 200 MeV p +

972 C.L. MorrisLos AlamosJ.A. McGillLos Alamos

"Low-Momentum Delta Production Viathe Reaction 13C(n+,p)12CA,"

973 G. PaulettaUniv. of Texas,Austin

M.M. GazzalyUniv. of MinnesotaN. TanakaLos Alamos

974 G. PaulettaUniv. of Texas,Austin

M.M. GazzalyUniv, of MinnesotaN. TanakaLos Alamos

975 L.-C. LiuLos AlamosM.J. LeitchLos Alamos

976 J.D. BowmanLos Alamos

"Search for Narrow Resonances inthe B=2 Missing-Mass Spectrum Fromp+He Reactions and in theExcitation Functions of the ppPion Production,"

"A Search for Narrow Resonances inthe B=2 System Using the3He(n+,p)MM and the2H(n+,lT')MM Reactions,"

"Single Charge Exchange withStopped Negative Pions,"

"Study of the Charged ParticleDecay of the Giant DipoleResonance Excited by Pion SingleCharge Exchange on 13C,"

305

APPbMDIXBNev\ Proposals Dunng 1985


977

978

979

G.J . igoUCLA

G.A Rebka, Jr.Univ. of WyomingJ.LMITP.ALos

C.L.Los

J.A.Los

. Matthews

.M. GramAlamos

MorrisAlamos

McGillAlamos

980 K.K. SethNorthwestern Univ.


982 R.A. LovemanUniv. of Colorado

983 D. WrightVPI and State Univ.

G.S. BlanpiedUniv. of South CarolinaM. BlecherVPI and State Univ.

984 R.J. PetersonUniv. of Colorado

985 C M . HoffmanLos AlamosJ.R. KaneColl. of William & MaryV.W. HughesYale University

"Measurement of WolfensteinParameters for Proton-DeuteronElastic Scattering at BOO MeV,"

"A Coincidence Measurement of PionDouble Charge Exchange:•»He(n+,JTp)3p-,"

"A Search for T=2 Diba^yonProduction in the d(Ji+,n~)XReaction,"

"An Investigation of theNear-Stability of 6H and 7H,"

"Do Bound States of Real PionsExist?"

"The Measurement of LightFragments from Pion TrueAbsorption,"

"n^-Tin and iTLead ElasticScattering at Energies Between 30and 65 MeV,"

"Pion Scattering to 8"States of 6 0Ni,"

Stretched

"Search for Muonium to AntimuoniumSpontaneous Conversion,"

306

APPENDIX BNew Proposals During 1985


986 J. LirtkeKFA-JULICH

987 J. LinkeKFA-JULICH

W. DelleKFA-JULICHW.F. SommerLos Alamos

"Spallation Neutron Irradiation ofNon-Oxide Ceramics for First-WallFusion Reactor Application,"

"Fast Neutron IrradiationScreening Test of PolycrystallineGraphites Under First-Wall FusionConditions,"

988 C.L. MorrisLos AlamosR. GilmanUniv. of Pennsylvania

989 K.S. DhugaNew Mexico State Univ

990 M.A. MoiriesterTel-AvivR. A. LovemanUniv. of ColoradoR.J. PetersonUniv. of Colorado

991 G.R. BurlesonNew Mexico State Univ

992 M.A. PlumLos Alamos

993 C.L. MorrisLos AlamosR.D. Ransoir.eRutgers Univ.

"Double-Isobaric-Analog Resonancein Heavy Nuclei,"

"Investigation of Energy and MassDependence of Large-AnglePion-Nucleus Elastic ScatteringAcross the Resonance Region,"

"Pion Single Charge Exchange onthe Deuteron,"

"Continuation of the Investigationof the Energy, Mass, and ChargeDependence of Pion-Nucleus ElasticScattering Near 180°,"

"Excitation Functions for MagneticTransitions in 24Mg and 28Si,"

"Study of it Absorption Below the3/2 R e s o n a n c e Region,"

307

APPENDIX B(Mew Proposals During 1985


994

995

996

997

C.L. MorrisLos AlamosR.D. RansomeRutgers Univ.

C.F. MooreUniv. of Texas,Austin

S.J. Seestrom-MorrisUniv. of Minnesota

"Study of n Absorption Above the^3/2 3/2 ^ e s o n a n c e Region,"

"Energy Dependence of n+ andn~ Scattering to Low-LyingStates in 208Pb,"

J.D. Zumbro "A Search for the 5Li+n~Univ. of Pennsylvania State in 5He,"

F.T. BakerUniv. of GeorgiaG.L. GlashausserRutgers Univ.K.W. JonesLos Alamos

"Spin-Flip Cross Section forInelastic Proton Scattering from12C and 160 at 319 MeV,"

998 C.L. MorrisLos AlamosD.K. DehnhardUniv. of Minnesota

999 A. FazelyLousiana State Univ.

L.-C. LiuLos Alamos

1000 D.K. DehnhardUniv. of Minnesota

K.W. JonesLos AlamosS.J. Seestrom-MorrisUniv. of Minnesota

"The 4He(n,rc'p)3He Reaction- A Test of Charge Symmetry,"

"Study of Pion Double ChargeExchange Reactions128Te(n+,iT)128Xe(g.s.) and13oTe(n+,n~)13OXe(g.s.)-,"

"Cross Sections for the (p,n+)Reaction on 1 2C, 1 3C, and14N,"

308

No. Spokesperson

APPENPiX BNew Proposals During 1985

Title

1001

1002

1003

1004

1005

1006

1007

E. PiasetzkyLos Alamos

H.W. BaerLos AlamosM.J. LeitchLos Alamos

B.J. DropeskyLos Alamos

L.-C. LiuLos Alamos

R.C. ReedyLos Alamos

J.C. PengLos AlamosJ.E. SimmonsLos Alamos

J.M. MossLos Alamos

G. PaulettaUniv. of Texas,Austin

M.W. GazzalyUniv. of MinnesotaN. TanakaLos Alamos

B.M.K.NefkensUCLA

"Study of Double-AnalogTransitions at Pion Energies 20 to80 MeV,"

"Energy Dependence of the(n+,2il+) Reaction in ComplexNuclei,"

"Production of Long-LivedRadionuclides by Stopped NegativeMuons,"

"Measurements of ri-Meson Mass inFree Space and in Nuclei,"

"Relativistic Effective MassRenormalizations of ContinuumPolarization Observables,"

"A Search for a Narrow Resonancein the B=2 System Using then+diup Reaction,"

"Comparison of NSF-Minimum inJT3H and n+3He ElasticScattering,"

W.J. BriscoeGeorge Washington Univ.

309

APPENDIX B


1008 F. IromLos Alamos

J.D. BowmanLos Alamos

1009 F.W. HersmanUniv. of NewHampshire

1010 F.T. BakerUniv. of Georgia

S.K. NandaUniv. of Minnesota




1014 A. HorsewellRiso Nat. Lab,Denmark

W.F. SommerLos Alamos

"Study of the Mass and EnergyDependence of Low Energy PionSingle Charge Exchage at 180°,"

"Pion Scattering From 206Pb—HowFar Can Pions Probe Into TheNuclear Interior?,

"Measurements of Spin-Flip CrossSection Angular Distributions forEv < 40 MeV in

124Sn,"

"Non Analog DCX - Systematics inHeavy Nuclei,"

"Study of Analog DCX on a8Sr,"

"Pion Production in the Continuumwith Polarized Protons,"

Proton, Spallation Neutron andFission Neutron Irradiation ofCopper

310

APPENDIX C

LAMPF Visitors During 1985

APPENDIX C:LAMPF Visitors During 1985

BjarneAas, UCLADavid L. Adams, UCLAGary S. Adams, Univ. of South CarolinaEric G. Adelberger, Univ. of WashingtonSteven D. Adrian, UCLAWanda Alberico, Univ. of TorinoRichard C. Allen, UC, IrvineJohn C. Allred, Consultant, New MexicoPeter W. F. Alons, Univ. of ColoradoJonas Alster, Tel Aviv Univ.Mohammed Ali Al-Solami, Univ. of South CarolinaAlan N. Anderson, EG&G, IdahoBryon D. Anderson, Kent State Univ.Mar}'E.Anderson, Univ. of New MexicoA. Ballard Andrews, Univ. of TexasHans-Jurgen Arends, Univ. of BonnKatsushi Arisaka, Univ. of PennsylvaniaRichard A. Arndt, Virginia Polytechnic Inst. & State Univ.Klaus-Peter Arnold, Univ. of HeidelbergMarina Artuso, Northwestern Univ.Daniel Ashery, Tel Aviv Univ.Leonard B. Auerbach, Temple Univ.Naftali Auerbach, Tel Aviv Univ.DavidA. Axen,TRlUMFMark G. Bachman, Univ. of TexasF. Todd Baker, Univ. of GeorgiaLeonce L. Bargeron, Univ. of PennsylvaniaBarry Barish, CaltechMartin L. Barlett, Univ. of TexasDavid B. Barlow, UCLABernd Bassalleck, Univ. of New MexicoMichael E. Beddo, New Mexico State Univ.Barry L. Berman, Lawrence Livermore Lab.William W. Bewley, UC, Riversideiarlochan S. Bhatia, Texas A&M Univ.Louis Bimbot, Univ. of ParisTerryJ. Black, Abilene Christian Univ.

Leslie C. Bland, Indiana Univ.Gary S. Blanpied, Univ. of South CaiolinaMarvin Blecher, Virginia Polytechnic Inst. & State Univ.MarekBleszynski, UCLADavidJ. Blevins, Consultant, New MexicoCarolus Boekema, Texas Tech Univ.Victor A. M. Brabers, Eindhoven Univ. of Tech.JeffreyT. Brack, Univ. of ColoradoMichael R. Braunstein, Univ. of ColoradoJoseph L. Breeden, Indiana Univ.Nance L. Briscoe, Nat. Bureau of StandardsWilliamJ. Briscoe, George Washington Univ.Michael A. Bryan, Univ. of TexasHoward C. Bryant, Univ. of New MexicoDavid V. Bugg.. Univ. of LondonMichael G. Burlein, Univ. of PennsylvaniaGeorge R. Burleson, New Mexico State Univ.MaryJ. Burns, Univ. of New MexicoJiri Bystricky, UCLAAugustineJ. Caffrey, EG&G,IdahoVanice A. P. Carlson, ArgonneKwai-Chow Bt amin Chan, Texas Tech Univ.Chung-Yun Chang, Univ. of MarylandHerbert H. Chen, UC, IrvineFrancis Chmely, Yale Univ.Katherine W. C. Choi, Louisiana State Univ.Steven B. Christo, Louisiana State Univ.Douglas E. Ciskowski, Univ. of TexasBenjamin L. Clausen, Univ. of ColoradoAnthonyS. Clough, Univ. of Surrey-Stanley Cohen, Drexel Univ.Joseph R. Comfort, Arizona State Univ.Genevieve R. Comtet, Centre Nat. de la Recherche Sci.James P. Connelly, Univ. of New HampshireDavid C. Cook, Univ. of Minnesota

Peter S. Cooper, Yale Univ.Hall L. Crannell, Catholic Univ. of America

311

APPENDIX GLAMPF Visitors During 1985

Gerard M. Crawley, Michigan State Univ.An-Zhi Cui, Insi. of Atomic Energy, PRCStephen T. CummingS, Univ. of TexasDian B. Curran, Univ of IowaDonald R. Cyborski, ArgonneJames A. DaltOU, Abilene Christian Univ.Sunayana Datta, Temple Univ.Craig K. Davidson, Jomar SystemsCharles A. Davis, TRIUMFAlfred R. de Angelis, Rutgers UnivDietrich K. Dehnhard, Univ of MinnesotaPeter P. Denes, Univ. of New MexicoArthur B. Denison, Univ. of WyomingKalvir Singh Dhuga. New Mexico State Univ.John F. Dicello, Clarkson Univ.John F. Dicello III, Clarkson Univ.PaulT. Dicello, Clarkson Univ.Byron D. Dieterle, Univ. of New MexicoBrenda L. Dingus, Univ. of MarylandNedS. Dixon, Franklin/Marshall Coll.Stanley A. Dodds, Rice Univ.PeterJ. Doe, UC, IrvineHermann J. Donnert, Kansas State Univ.Edward G. Donoghue, Rutgers Univ.David W. Dryer, ArgonneHendrikM. Duiker, Univ. of ColoradoMorton Eckhause, Coll. of William & MaryRobert W. Ellsworth, George Mason Univ.Jon M. Engelage, UCLAPeter A. J. Englert, Univ. of KolnDavidJ. Ernst, Texas A&M Univ.Jorge A. Escalante, Univ. of South CarolinaJohn A. Faucett, New Mexico State Univ.Ali Fazely, Louisiana State Univ.Alan E. Feldman, Univ. of MarylandRaymond W. Fergerson, Rutgers Univ./Univ. of TexasWilliam J. Fickinger, Case Western Reserve Univ.John M. Finn, Coll. of William & Mary-Randall J. Fisk, Valparaiso Univ.Gottfried Flik, Max Planck Inst.

Carlos A. Fontenla, New Mexico State Univ.H. Terry Fortune, Univ. of PennsylvaniaMichael A. Franey, Univ. of MinnesotaStuartJ. Freedman, ArgonneLinda S. Fritz, Franklin/Marshall Coll.Brian K. Fujikawa, CaltechHerbert O. Funsten, Coll. of William & MaryRaffaelloGarfagnini, Univ. DegH studiJuan R. Garza, Univ. of TexasM. Magdy Gazzaly, Univ. of MinnesotaDonald F. Geesaman, ArgonneRobert A. Giannelli, Arizona State Univ.Edward F. Gibson, California State Univ.Ronald A. Gilman, Univ. of PennsylvaniaJohn F. Ginkel, Coll. of William & MaryGrant A. Gist, Rice Univ.Charles M. Glashausser, Rutgers univ.George Glass, Texas A&M Univ.RoyJ. Glauber, Harvard Univ.Eduardo Gonzalez-Hernandez, Univ. of TexasJordan A. Goodman, Univ. of MarylandJeffreys. Gordon, UCLAKrishnaswamy N. Gounder, Univ. of South CarolinaScott C. Graessle, Abilene Christian Univ.Karl-Heinz Graf, KFAAndrew A. Green, Rutgers Univ.ChiltonB. Gregory, Univ. of New MexicoDavid P. Grosnick, Univ. of ChicagoFranz L. Gross, Coll. of William & MarySunil K. Gupta, Univ. of MarylandPaul P. Guss, Coll. ofWilliam & MaryWilliam N. Haberichter, ArgonnStephen L. Hall, Abilene Christian Univ.Aksel L. Hallin, Princeton Univ.Ronnie W. Harper, Ohio State Univ.EdkK. Heide, Univ. of MinnesotaJohn Walker Heimaster, Ohio State Univ.F. William Hersman, Univ. of New HampshireMartin Hesche, Univ. of InnsbruckJohn C. Hiebert, Texas A&M Univ.

312

APPENDIX C


Virgil L. Highland, Temple Univ.Daniel A. Hill, ArgonneRoger E. Hill, Univ. of New MexicoNorton M. Hintz, Univ. of MinnesotaGerald W. Hoffmann, Univ. of TexasSteinarHoibraten, MITBoR. Hoistad, Gustaf Werner Inst.Karl F. Holinde, Univ. of BonnCharles L. Hollas, Univ. of Texa.,Barry R. Holstein, Univ. of MassachusettsJames A. Holt, Texas ASM UnivAndy Horsewell, KIMI National Lab.Ying-Chiang David Huang, Temple Univ.E. Barrie Hughes, Stanford UnivVernon W. Hughes, Yale Univ.Charles R. Hummer, Univ. of ConnecticutGeorgeJ. Igo, UCLA

Richard L. Imlay, Louisiana State Univ.Robert L.Jaffe, MITMarkJ.Jakobson, Univ. of MontanaRandolph H.Jeppesen, Univ. of MontanaKenneth F. Johnson, Argonne

CarolJ. Johnstone, Univ. of New MexicoMark K.Jones, Univ. of MinnesotaSteven E.Jones, Brighani Young Univ./KG&G, IdahoJanKallnejETJohn R. Kane, Coll. of William & MaryJu Hwan Kang, Univ. of New MexicoPaulJ. Karol, Carnegie Mellon Univ.Thomas E. Kasprzyk, ArgonneJamesJ. Kelly, Univ. of Man landRobert A. Kenefick, Texas A&M UnivChristopherJ. Kenney, Coll. of William & MarySteve H. Kettell, Yale UnivEdward R. Kinney, MITLeonards. Kisslinger, Carnegie Mellon UnivAmir Klein, Soreq Nuclear Research CenterJames N. Knudson, Arizona State Univ.Dale S. Koetke, Valparaiso Univ.Donald D. Koetke, Valparaiso Univ.

Donald K. Kohl, Consultant, New MexicoKathryn L. Kolsky, Carnegie-Mellon Univ.DanielS. Koltun, Univ. of RochesterMichael A. Kovash, Univ. of KentuckyRoberts. Kowalczyk, ArgonneStanley B. Kowalski, MITHeribert Koziol, CI-RN

Daniel A. Krakauer, Univ. of MarylandRobert H. Kraus, Clark Univ.Laura L. Kropp, Valparaiso UnivYunan Kuang, Yale Univ.Barry D. Kuban, Ohio state Univ.KrishnaS. Kumar, Syracuse Univ.A. Raymond Kunselman, Univ. of WyomingPeter H. Kutt, Univ. of PennsylvaniaGary S. Kyle, New Mexico State Univ.MasoudR. Laghai, Univ. of New MexicoRobert A. Lamb, Univ. of SurreyK. Dean Larson, Univ. of New MexicoNabilA.-F. Lasheen, Univ. of South CarolinaJuergen F. Last, ArgonneChristopher P. Leavitt, Univ. of New MexicoWen-PiaoLee, UC, IrvinePaul A. Lennous, Ohio State Univ.FriederLenz, SINKevin T. Lesko, Lawrence Berkeley Lab./ArgonneJechiel Lichtenstadt, Tel Aviv Univ.Roger L. Lichti, Texas Tech Univ.B.Joseph Lieb, George Mason Univ.David A. Lind, Univ. of ColoradoV. Gordon Lind, Utah state Univ.Richard A. Lindgren, Univ. of MassachusettsAlanG. Ling, UCLATa-Yung Ling, Ohio State Univ.John D. Linsley, Univ. of New MexicoStanley Livingston, Consultant, New MexicoVladimir M. Lobashev, Inst. of Nuclear Research,USSRDonald E. Lobb, Univ. of VictoriaWolfgang Lohmann, KFADavid Lopiano, UCLA

313

APPENDIX C

LAMPF Visitors Pui'pq

William G. Love, Univ. of GeorgiaRobert A. Loveman, Univ. of ColoradoChris B. Luchini, New Mexico State Univ.Li-Ping Lung, Univ. of MinnesotaChristopher R. Lyndon, Coll of William s MaryMalcolm H. MacFarlane, Indiana Univ.Anthony M. Mack, Univ. of MinnesotaJohn R. Mackenzie, Florida State Univ.Douglas E. Maclaughlin, uc, RiversideMaureen P. Madden, ArgonneRichard M a d e y , Kent state I'niv

Kazushige Maeda, Tohoku Univ.John H. Manley, Consultant, New MexicoJeremy Margulies, sueJohn K. Markey, Yale Univ.Richard M. Marshall, Univ. of VirginiaWilliam G. Marterer, Louisiana State Univ.HowardS. Matis, Lawrence Berkeley Lab.June L. Matthews, MITBjorn E. Matthias, Yale Univ.Bill W. Mayes, Univ. of HoustonJoseph W. McDonald, Univ. of TexasJames E. McDonough, Temple Univ.W. Kenneth McFarlane, Temple UnivRobert D. McKeown, CaltechJames T. McKinley, Univ. of MontanaBrent G. McMillan, Abilene Christian Univ.Kok-Heong McNaughton, univ. of TexasKatie M. McShana, ArgonneWilliamJ. Metcalf, Louisiana State Univ.Jason S. Meyer, Univ. of Mar>'landDaniel W. Miller, Indiana Univ.Ralph C. Minehart, Univ. of VirginiaChandrashekhar Mishra, Univ. of South CarolinaTanuja Mishra, Univ. of South CarolinaJoseph H. Mitchell, Univ. of ColoradoJoseph W. Mitchell, Ohio State Univ.Keith E. Mitchell, Abilene Christian Univ.William A. Mitchell, Ohio State Univ.Murray A. Moinester, Tel Aviv Univ.

AlirezaMokhtari, George Washington Univ./UCLAWilliam R. Molzon, Univ. of PennsylvaniaC. Fred Moore, Univ. of TexasTroyD. D. Moore, Abilene Christian Univ.Shaul Mordechai, Univ. of TexasSheila L. Morris, Univ. of TexasLeif K. Morton, Abilene Christian Univ.MoshiG. Moshi, UCLASanjoyMukhopadhyay, Northwestern Univ.Takemi Nakagawa, Tohoku Univ.Sirish K. Nanda, Univ. of MinnesotaJamesJ. Napolitano, ArgonneSubrata Nath, Texas A&M Univ.Itamar Navon, Tel Aviv Univ.Bernard M. K. Nefkens, UCLAJames E. Nelson, ArgonneCharles R. Newsom, Univ. of IowaBenwen Ni, Yale Univ.Michael Nicholas, Univ. of MississippiM. Edward Nieland, Iowa state Univ.Erik A. Nilsson, Gustaf Werner Inst.KunihikoNishiizami, uCSan DiegoEric B. Norman, Lawrence Berkeley Lab.Lee C. Northcliffe, Texas A&M Univ.David S. Oakley, Univ. of TexasYuji Ohashi, Argonne/UCLAHajime Ohnuma, Tokyo Inst. of Tech.Jean M. Oostens, Univ. of Cincinnati/Illinois Inst. of Tech.Herbert Orth, Yale Univ.Brett L. Parker, Univ. of MassachusettsGianni Pauletta, Univ. of TexasSeppo I. Penttila, Univ. of TurkuCharles F. Perdrisat, Coll. of William & MaryRoyJ. Peterson, Univ. of ColoradoAnne M. Petrov, George Washington Univ.Eliazer f <asetzky, Tel Aviv I'niv.Gerard M. Pignault, Univ. of South CarolinaChandraseghara T. G. Pillai, UCLADinko Pocar, ic, Stanfo.a Univ.NorbertT. Poriie, Purdue Univ.

314

APPENDIX C


Michael E. Potter, uc, IrvineBarry M. Preedom, Univ. of South CarolinaVina A. Punjabi, Coll. of William S MaryMichaelJ. Purcell, Univ. of TexasThomas M. Putnam, Consultant, New MexicoMohini W. RaWOOl, New Mexico State Univ.Glen A. Rebka, L'niv. of WyomingRobert P. Redwine, MITPaul L. Reeder, Battelle Pacific Northwest Lab.Randolph A. Reeder, I'niv. of New MexicoJamesJ. Reidy, Univ. of MississippiHorst Dieter Retnpp, Max -Planck Insi.James H. Richardson, Consultant, New MexicoJoan A. Rifley, Univ. of TexasPeterJ. Riley, Univ. of TexasRobert A. Ristinen, Univ. of ColoradoBarry G. Ritchie, Arizona State Univ.Michael W. Ritter, Stanford Univ.Warren M. Roane, Abilene Christian UnivDonald A. Roberts, Univ. of WyomingKathleen A. Roemheld, uc, IrvineSayed H. Rokni, Utah State Univ.Thomas A. Romanowski, Ohio State Univ.Philip G. ROOS, Univ. of MarylandDennis Rothenberger, Arizona siaie Univ.NadineA. Roy, ArgonneCharlesJ. Rush, Ohio state Univ.Moustafa K. Saber, Northwestern Univ.Michael E. Sadler, Abilene Christian Univ.David P. Saunders, Univ. of TexasH. Reiner Schaefer, Yale Univ.John P. Schiffer, ArgonneKarlheinz Schindl, CERNStuart W. Schmidt, ArgonneSusan J. Seestrom-Morris, Univ. of MinnesotaColinJ. Seftor, George Washington Univ./UCLARalph E. Segel, Northwestern Univ.Peter A. Seidl, Univ. of TexasUrsJ. Sennhauser, SINKamal K. Seth, Northwestern Univ.

M. Hassan Sharifian, Univ. of New MexicoTomikazu Shima, ArgonneHajime ShimiZU, Tokyo Inst. of Tech.Karam Ali Shojaei, Virginia state Univ.Rickey L. Shypit, Univ. of SurreyEdward R. Siciliano, Univ. of GeorgiaMargaret L. Silbar, Consultant, New MexicoElton S. Smith, Ohio State Univ.KaleenJ. Smith, Abilene Christian Univ.L. Cole Smith, Univ. of VirginiaWinthropW. Smith, Univ. of ConnecticutMichael J. Smithson, Univ. of TexasW. Rodman Smythe, Univ. of ColoradoDaniel I. Sober, Catholic Univ. of AmericaTroySoos, MITPaul A. Souder, Syracuse Univ.Rayappu Soundranayagam, Northwestern univ.Franz Sperisen, 'JCLAJoseph F. Speth, KFAHarold M. Spinka, ArgonneRobert W. Stanek, ArgonneMichael P. Staskus, Univ. of ColoradoMary Beth Stearns, Arizona State Univ.Rolf M. Steffen, Purdue Univ.George S. F. Stephans, MITJames E. Stewart, Univ. of New MexicoNoel M. Stewart, Univ. of LondonCarey E.Stronach, Virginia State Univ.Richard L. Talaga, Univ. of MarylandPeter C. Tandy, Kent state Univ.Robert L. Tanner, Consultant, New MexicoMorton F. Taragin, George Washington Univ.T. Neil Thompson, UC, IrvineJames M. Thome, Brigham Young Univ.MarkTimko, Ohio state Univ.W. Bradford Tippens, Texas A&M univ.John A. Tjon, Univ. of UtrechtJohnW.Tobin, New Mexico State Univ.Gerald E. Tripard, Washington State Univ.ChristophTschalar, SIN

315

APPENDIX C

.. AMF'F . r:,ik-.i-

R. Steven Turley, Hughes Research Lab.JeffT. Ui, Louisiana State Univ.John L. Ullmann, Univ. ot ColoradoDavid G. Underwood, ArgonneGerrit Van Kalkeren, uc, RiversideJay W. Van Orden, Univ. ot MankindClinton D. VanSiclcn, v.c&c,IdahoGordonJ. Vandalen, uc. RiversideKamran Vaziri, Utah siaie Univ.

BruceJ. VerWest, Arco t)il & Gas Co.

Victor \i. Viola, Indiana Univ.

Stephen Von Molnar, IBM Watson Research CenterWilliam F. Vulcan, Coll. of William & Man-Roberta J. Wade, Univ. of New MexicoJohn D. Walecka, Stanford Univ.Robert L. Walker, Consultant, New MexicoAngel T. M. Wang, UCLAKen-Chung Wang, uc, IrvineSou-Tien Wang, Wang NMR.lnc.Yea-Fei Wang, Wang NMR.IUC.

Zhi-Fu Wang, lnst. of Atomic Energy, PRCRay A. Warner, Battelle Pacific Northwest Lab.Douglas L. Watson, Univ. of BradfordJohn W. Watson, Kent State Univ.Monroe S. Wechslcr, Iowa State Univ.Robert C. Welsh, George Mason Univ.Charles A. Wert, Univ. of IllinoisC. Steven Whisnant, Univ. of South Carolina

D. Hywel White, BrookhavenR. Roy Whitney, Univ. of VirginiaCharles A. Whitten, UCLA

RobertJ. Whyley, Coll. of William & MaryBryan H. Wildenthal, Drexel UnivAllen L. Williams, Univ. of TexasKentnerB. Wilson, Consultant, New MexicoRobert R. Wilson, Columbia Univ.Andreas Wirzba, SUNY, stony BrookFred K. Wohn, Iowa State Univ.Stephen A. Wood, Tel Aviv univ.KimA. Woodle, Yule Univ.James N. Worthington, Jenworth Co.Bryan K.Wright, Univ. of VirginiaDennis H.Wright, Virginia Polytechnic Inst. & State Univ.S. Courtenay Wright, Univ. of ChicagoShen-WuXu, Univ. of TexasMing-Jen Yang, Univ. of ChicagoSergei K. Yesin, Inst. of Nuclear Research, USSRAkihiko Yokosawa, ArgonneJinnan Yu, Inst. of Atomic Energy, PRCChris D. ZafiratOS, Univ. of ColoradoLarry Zamick, Rutgers Univ.Benjamin Zeidman, ArgonneHansJ.Ziock, UCLA

Klaus O. H. Ziock, Univ of VirginiaRobert Ziock, UCLAJohn D. Zumbro, Univ. of Pennsylvania

316

APPENDIX C


Progress at LAMPF is the progress report of MP Division of Los AlamosNational Laboratory. In addition it includes brief reports on research done atLAMPF by researchers from other institutions and Los Alamos NationalLaboratory- divisions.

Progress at LAMPF is published annually on April 1. This schedule requiresthat manuscripts be received by January 1.

Published material is edited to the standards of the Style Manual o( theAmerican Institute of Physics. Papers are not refereed, hence presentation inthis report does not constitute professional publication of the material nordoes it preempt publication in other journals. Readers should recognize thatresults reported in Progress at LAMPF are sometimes preliminary or tentativeand that authors should therefore be consulted in the event that these resultsare cited.

Contributors can expedite the publication process by giving special care tothe following specifics:

1. When possible, furnish computer files for text and MAPPER files forillustrations together with a hardcopy of your paper. Progress at LAMPFcan accept files from computers, stand-alone word processors, andpersonal computers. TgX files are especially welcome.

2. Drawings and figures submitted should be of quality suitable for directreproduction after reduction to single-column width, 55 mm(2 1/4 in.). MAPPER files should be printed on laser printers.

3. Figure captions and table headings must be furnished. The A1PStyleManual requires that every figure have a caption that is "complete andintelligible in itself without reference to the text."

4. References must be complete and accurate. If a reference cites a papersubmitted for publication, the title of the paper must be given. Labora-tory standards prefer six authors before et al. in reference lists.

For legal reasons the term private communication cannot be used inP' gress at LAMPF. Credit for unpublished information may be given infootnotes provided the name, organization, and date are cited.

5. Abbreviations and acronyms should be avoided if possible (in figuresand tables as well as text), and when used must be defined.

6. All numerical datashould be given in SystemeInternational (SI) units.

~\ Authors are reminded that it helps the reader to have an introduction,which states the purpose(s) of the experiment, before presentation ofthe data.

Information for Contributors

317

APPENDIX GLAMPF Visitors Dui ing 1Q85

Research reports should be brief but complete. A list of recent publicationsrelating to the experiment, for separate tabulation in this report, is muchappreciated.

Contributors are encouraged to include as authors all participants inexperiments so that they may receive credit for authorship and participation.

Questions and suggestions should be directed tojohn C. Allred, LosAlamos National Laboratory, MS H850, Los Alamos, NM 87545.

318

progress at lampf - ipen

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