accelerator technology in line with national interests

ACCELERATOR TECHNOLOGYIN LINE WITH

NATIONAL INTERESTS

PROBING THE STRUCTURE OF MATTER

FOR DEFENSE, INDUSTRY, AND BASIC SCIENCE

L os Alamos is refocusing the mission of its acceleratorcomplex to respond to the increased national need for a

steady and reliable source of neutrons for defense andcivilian applications. Along with its new mission, theaccelerator complex has acquired a new name: the LosAlamos Neutron Science Center, or LANSCE. The newfacility will take full advantage of existing infrastructure andaccelerator technology developed at Los Alamos over thelast 50 years, while incorporating new design features tomake LANSCE the most advanced neutron-scatteringfacility in the world. Neutron scattering — a reaction inwhich neutrons are scattered by target nuclei rather thanabsorbed by them — is one of the most effective tools forelucidating the structure and dynamics of physical andbiological materials.

M A R C H - A P R I L I S S U E 1 9 9 6

1

A MONTHLY PUBLICATION OF THEPUBLIC AFFAIRS OFFICE OF

LOS ALAMOS NATIONAL LABORATORY

LOS ALAMOS NATIONAL LABORATORY, AN AFFIRMATIVE ACTION / EQUAL OPPORTUNITY EMPLOYER, IS OPERATED BY THE UNIVERSITY OF CALIFORNIA FOR THE U.S. DEPARTMENT

OF ENERGY UNDER CONTRACT NO. W-7405-ENG-36

LOS ALAMOS NATIONAL LABORATORY PUBLIC AFFAIRS OFFICE, MS-A118

LOS ALAMOS, NM 87545


2

EDITORDiane Banegas

MANAGING EDITORMeredith Coonley

(505) 665-3982 • [email protected]

STAFF WRITERTheresa Salazar

PHOTOGRAPHYJames Rickman • LeRoy N. Sanchez

Los Alamos National Laboratory archives

CONTRIBUTING EDITORSDaniel Rusthoi • Stephen Sterbenz • Daniel Weinacht

CONTRIBUTING WRITERSJoe Bowden • Steve Sandoval • Kelly Stoddard

PRINTING COORDINATORG.D. Archuleta


PUBLIC AFFAIRS OFFICE, MS P355

LOS ALAMOS, NM 87545

The Los Alamos Neutron Science Center acceleratorhas produced particle beams for hundreds of experi-ments and thousands of scientists worldwide for nearlya quarter of a century.

Commissioned in 1972 as “LAMPF,” or the Los AlamosMeson Physics Facility, it is still the most powerful linearproton accelerator in the world, with an output powerof about one megawatt. To create neutrons for theneutron-scattering facility, part of this powerful accelera-tor beam is channeled through a proton storage ring tocreate more intense and shorter “bunches” of protons.

One application of neutrons produced via acceleratortechnology is currently under review by the U.S.

Department of Energy as a safe, cost-effective way of meeting the nation’slong-term tritium supply for nuclear weapons. Tritium — a radioactiveform of hydrogen — boosts the explosive power of nuclear warheads.The United States needs a reliable, continuous supply of tritium to main-tain its smaller, post-Cold War stockpile of nuclear weapons.

Until 1988, tritium came from dedicated DOE production reactors thathave since been rendered inactive. With no new nuclear weapons in pro-duction and the U.S. moratorium on nuclear testing, currentrequirements are being met by recovering tritium from dismantled

ÕProtons at the

Los Alamosacceleratorbegin their

journey here, inthe domes at

the top ofthree of these

Cockcroft-Walton

accelerators. Bythe t ime the

part ic les leavethis sect ion,

they have beenaccelerated to

7,440 milesper second

(4 percent ofthe speed ofl ight) . From

here, the beamspass through

low-energytransport

systems wherethey aresteered,

focused, andbunched for

inject ion intothe second

stage of theaccelerator.

This photo alsoappears on the

cover ofthis issue.


weapons. But tritium is radioactive and decays at about 5.5 percent ayear, so a new tritium production facility must be operating within thenext 10 years to sustain the remaining weapons and maintain the U.S.nuclear deterrent.

Only two practical systems exist that can make enough neutrons to pro-duce tritium: reactors and accelerators. In a reactor, nuclear fissionsupplies the neutrons. Accelerators avoid the use of fissilematerial, an advantage that eliminates any chance of a criti-cality accident and avoids the generation of high-levelnuclear waste.

Los Alamos is leading a multi-laboratory effort to designand develop a low-energy demonstration accelerator atLANSCE, which will serve as a prototype for the tritium-production system proposed for the DOE’s Savannah RiverSite in South Carolina.

The need for the U.S. to maintain a safe and reliable nuclearweapons stockpile for the indefinite future in the absence of nuclear test-ing presents a significant new challenge to the DOE weapons complex.

Careful attention to the underlying science and the production processis required for scientists to provide dependable certification of theenduring stockpile as it ages substantially beyond its originally envi-sioned lifetime or undergoes gradual replacement with units producedby different plants and processes than the original ones.

Retaining confidence in the safety and reliability of weapons in the agingstockpile can only be derived from a thorough understanding of thephysical processes that bring about a nuclear explosion.

The DOE’s Stockpile Stewardship and Management Program has beendeveloped to address these challenges. A broad range of capabilities suchas plutonium chemistry and metallurgy, high-performance computing,and dynamic experimentation are required to carry out this program.LANSCE is a critical component of this program, providing intense neu-tron and proton beams for a broad range of weapons applicationsassociated with stockpile assessment and refurbishment.

In addition to defense research activities, neutrons are an indispensabletool to civilian researchers. LANSCE will contribute to many scientificfields, including condensed matter physics, materials science, chemistry,fundamental nuclear and particle physics, structural biology,engineering, and geology.

3

ÕA v iew of theinter ior of thesecond stage ofthe Los Alamosaccelerator , thedr i ft-tube l inac,where part ic lesare acceleratedto 80,000 mi lesper second(43 percentof the speedof l ight ) .

Neutrons, which reside in the nucleus of an atom,are equal in mass to their proton neighbors, butunlike protons, or electrons that orbit the nucleus,they carry no charge. This neutrality means neutronsare a very penetrating, thus useful, form of radiation.Neutron-scattering technology is complementary toX-ray diffraction, electron microscopy, magnetic res-onance, and other technologies used to probestructures on a microscopic level.

Neutron scattering is important for the study ofhigh-temperature superconductors, polymers, new-

generation catalysts, and magnetic materials. Neutrons also have a keyrole to play in clarifying the relationship between biomolecular struc-ture and function. This knowledge is crucial to advancements inmodern molecular medicine and biotechnology.

The LANSCE facility will allow industrial scientists to incorporate neu-tron scattering into manufacturing processes for commercial productssuch as automotive parts, steel bearings, tire rubber, polymer solutionsfor oil recovery, and magnetic films for next-generation magnetic storagedevices. LANSCE will allow comprehensive and detailed studies ofresidual and induced strains in engineered components and permit thehistory of fabrication to be followed.

A unique capability that has been developed at LANSCE is the measure-ment of transmission diffraction spectra using a single beam pulse. Thismethod has already been used to study the phase evolution that is partof the preparation of a special tough steel used for ball bearings and tosuggest changes to the manufacturing process that would reduce thetime and energy needed.

A team of IBM and Los Alamos scientists working at LANSCE has dis-covered that irradiating high-temperature superconductors withenergetic protons significantly improves their critical current-carryingcapability, making their use in practical applications more realistic.

A great advantage of a research facility based at a proton accelerator isthat the multiple research and development activities can be carried outsimultaneously. This allows the synergism between different disciplinesto be exploited, and permits ideas to flow between academic, industrial,and defense sectors.

◆


4

ÕThe th ird andlongest stage

of theaccelerator i s

the s ide-coupled-cav ity

l inac, whereprotons are

accelerated totheir f ina lenergy of

800,000,000electron volts ,moving about157,000 mi les

per second(84 percent of

the speedof l ight ) .

5


A HISTORY OFACCELERATORS AT LOS ALAMOS

IT’S A PARTICLE WORLD AFTER ALL

I n spite of many advances in accelerator technology over the last 50 years, the basic principle of particle

acceleration remains simple: An electric field surrounds abeam of charged particles — typically protons or electrons— and accelerates them to higher and higher energies. Although the basic principle of particle acceleration is simple, executionis not. Designing an accelerator requires creativity and ingenuity, andoperating an accelerator is sometimes more an art than a science.Accelerators fall into two categories: linear or circular. The linear accel-

erators, or linacs, move particles in a straight line. Thisdesign was first developed by Rolph Wideröe in 1928and later refined by Luis Alvarez. The circular machinemoves particles in a doughnut-shaped path. ErnestLawrence conceived this design in 1929 and dubbed hisinvention the “cyclotron.”

Accelerators havebeen work horses at

Los Alamos since the Laboratory’sinception. As early sources of neutrons,accelerators were used to direct low-energy beams on light elements such aslithium to study the nuclear reactionsrelevant to weapons physics. Fouraccelerators arrived at Los Alamos in

ÕThree ofthe f ive

acceleratorsused at Los

Alamos dur ingWorld War I I .

C lockwise fromthe top:

the HarvardCyc lotron

the I l l ino isCockcroft-

Walton,and the

Wiscons inShort Tank.

the spring of 1943: a Cockcroft-Waltonfrom the University of Illinois, whichproduced neutrons of 2.5 million elec-tron volts; two Van de Graaffs from theUniversity of Wisconsin, which pro-duced neutrons with energies between afew hundredths of an MeV and severalMeV; and a cyclotron from HarvardUniversity, which produced neutronswith even lower energies.

These accelerators made it possible forthe Manhattan Project scientists todetermine the critical masses of pluto-nium and uranium. Both fuels were soscarce that direct measurements wereimpossible. Another challenge was tofind a way of preventing a “fizzle,” or

predetonation, in the plutonium bomb — a problem that could arisefrom the spontaneous fission of fuel impurities. The accelerators made itpossible for the scientists to study neutron-induced fission at all therelevant neutron energies.

In December 1944, Los Alamos acquired a circu-lar electron accelerator known as a betatron. Thebetatron provided X-ray-like images of a mocksphere of fuel during implosion. This diagnostictechnique helped solve the problem of unevencollapse in the implosion weapon design that ulti-mately became “Fat Man.”

After World War II, Los Alamos retained three ofthe wartime accelerators and built a high-energyVan de Graaff accelerator to replace one of theWisconsin models, which went home after thewar. As relations between the United States andthe former Soviet Union went into a deep freeze,the Laboratory built two electron linacs toprovide radiographs of the implosion process inthermonuclear bombs.

That work eventually led to construction in 1963of PHERMEX — pulsed high-energy radiographic

6


ÈThe vert ica l Van

de Graaffaccelerator .

Recent ly shutdown, the

accelerator wasin use at

Los A lamos for40 years .

A Cockcroft-Waltonaccelerator .

Ô

machine emitting X-rays— a huge electron acceler-ator that generates X-raysby accelerating an electronbeam into a tungstentarget. Still in operation atLos Alamos, PHERMEXwas used recently to studythe strength of ceramictank armor.

In 1946 the first proton linac, designed by Alvarez, was built at theUniversity of California. A linac accelerates charged particles with aseries of electrical pushes, each of which increase the particles’ energyby an amount that is small compared to the total energy gain desired.

The Alvarez designwould later formthe drift tube linac,or the guts of thelow-energy portionof “LAMPF,” theClinton P. AndersonMeson PhysicsFacility, built on amesa top at LosAlamos NationalLaboratory in thelate 1960s.

If the World War II accelerators were scientific work horses, thenLAMPF has been the nuclear physics communi-ty’s work elephant for more than two decades.

Los Alamos physicist Louis Rosen, the chiefarchitect of LAMPF, proposed the idea of a newhigh-intensity proton accelerator in 1962. Sincemost accelerators at that time were beingdesigned to achieve higher energies per particlerather than more particles per unit time, Rosenpredicted such a facility would supply an abun-dance of particles known as pi mesons to studyin new ways nuclear interactions and the

7


ÓThe LAMPFbeam channel i sexcavated in1969.

Louis Rosen(standingcenter r ight )and othersce lebrate asthe LAMPF l inacproduces i tsf i rst 800 MeVbeam onJune 9, 1972.

Ô

ÈAn aer ia l v iewof the LAMPFcomplex and

thesurrounding

mesas.

structure of nuclei. The idea quicklygained support among his colleagues.

A small Los Alamos team led byDarragh Nagle and Ed Knapprejected a number of different designsbefore perfecting a design in 1965known as the side-coupled cavitylinac that could accelerate high-inten-sity beams of protons to 800 MeV. In1967 a working prototype proved theviability of their concept and con-struction began on LAMPF, a half-mile-long linear accelerator thatgenerates a medium-energy proton beam more intense than any otherbeam in the world.

The ground-breaking for LAMPF was held on Feb. 15, 1968. Thefacility was completed four years later and officially named theClinton P. Anderson Meson Physics Facility because of the late NewMexico senator’s long-time interest in and support of Los AlamosNational Laboratory.

Los Alamos recentlyrefocused the accel-erator’s mission toserve the nation’sneed for a steadyand reliable sourceof neutrons fordefense and civilianapplications. Byupgrading LAMPF’sexisting facilities,scientists can use

proton-induced spallation of heavy-metal nuclei to produce an intensesupply of neutrons over a range of energies.

LAMPF was built nearly 25 years ago to study nuclear reactionsinvolving energetic protons or pions. Now one of those reactions —proton-induced spallation — is the basis of a new neutron-scatteringfacility to be built at Los Alamos. That facility is “LANSCE,” the LosAlamos Neutron Science Center. ◆

8


ÕThe s ide-coupledcav it ies , wherehighly intensepulses ofprotons areaccelerated to800 MeV.

ÈAn exper iment

hal l at theManuel Lu jan

Jr . NeutronScatter ing

Center .


LANSCE LAUNCHESRESEARCH CRITICAL TO

STOCKPILE STEWARDSHIP ACCELERATOR FACILITY PROVIDES INTENSE

NEUTRON AND PROTON BEAMS

FOR A BROAD RANGE

OF WEAPONS APPLICATIONS

T he one-year-old stockpile stewardship program at the Los Alamos Neutron Science Center has already made

significant contributions to the Department of Energy’sStockpile Stewardship and Management Program. By providing intense neutron and proton beams for a broadrange of weapons applications associated with stockpileassessment and refurbishment, LANSCE is a key nationalresource for maintaining confidence in the nuclear weaponsstockpile in the absence of nuclear testing.The Stockpile Stewardship and Management Program focuses on fivecritical issues:

◆ Annual certification of performance and reliability — Ensuringthat the weapons in the stockpile are capable of fulfilling their deter-rence missions.

◆ Safety — Characterizing how weapons would perform in unusual andadverse conditions, such as an accident.

◆ Stockpile aging — Predicting the effects of aging on a weapon’s perfor-mance and reliability, and knowing how to respond with appropriatelife-extension measures.

◆ Weapon rebuilding and small-scale production — Maintaining thecapacity to rebuild stockpiled weapons and replace any weapons thathave been destroyed in the surveillance process.

◆ Ensuring a tritium supply — Producing a sufficient inventory of tri-tium, which is critical to the long-term availability and performance ofnuclear weapons.

This article discusses seven research areas at LANSCE and their importance to these critical issues.

9

DYNAMIC RADIOGRAPHY

Without nuclear testing, the only means available for studying the integral performance of a weapon during implosion is hydrodynamictesting. For many years, X-ray radiography has been a key diagnostictool for these tests. However, the current need for more detailed infor-mation pushes X-ray technology into a very challenging realm. Usinghigh-energy proton beams instead of X-rays as radiographic tools is nowbeing explored by LANSCE researchers as a more powerful means oftaking dynamic “snapshots” of implosion experiments at a future facility.This research will have an important bearing on annual certification,safety, and stockpile aging issues.

STATIC RADIOGRAPHY

FOR NONDESTRUCTIVE SURVEILLANCE

Certifying weapon components in an aging stockpile requires informa-tion on the condition of light weapons materials, such as hydrogen, thatlie inaccessible under dense materials, such as uranium. Radiographictechniques that use neutrons in a manner analogous to CAT scan technology probe nondestructively the mechanical structure of thelighter materials and eliminate the need to disassemble the part.LANSCE scientists are exploring the use of fast, thermal, and cold neutrons for a number of surveillance applications.

WEAPONS NUCLEAR DATA

Nuclear physicists at LANSCE are using an advanced gamma-ray detector array in conjunction with high-energy neutron beams for thefirst time anywhere. With this array, they will explore nuclear processes

relevant to nuclear weapons and help interpret theimpressive archive of diagnostic measurements leftbehind by a long history of nuclear weapons testing.

By measuring nuclear cross sections not easilyaccessible by other means, they will provide precisebenchmarks for the sophisticated weapons simula-tion codes needed to certify the safety andreliability of the aging stockpile. The AcceleratorProduction of Tritium program will benefit fromsimilar benchmarking studies carried out withother detector instruments at LANSCE.


10

The GErmaniumArray for

Neutron- InducedExc itat ions

(GEANIE) i s amult i -mi l l iondol lar , h igh-

eff ic iency, h igh-resolut ion,gamma-ray

detector arrayused in weapons

nuclear datastudies at

LANSCE.

Ô


WEAPONS MANUFACTURING PROCESS STUDIES

Neutron scattering techniques at LANSCE can assess the quality, unifor-mity, performance, and expected lifetime of weapons components.These capabilities will be increasingly important for stockpile certifica-tion, aging, and rebuilding, since manyreplacement parts will be manufacturedby new production processes in a differ-ent production complex.

Many components are fabricated usingcasting, forging, welding, and brazingprocesses. These processes produceresidual internal stresses that may affecta part’s response to shock, thermal cycling, radiation, and other environ-mental conditions. A LANSCE technique called neutron diffractometryprovides the only means of obtaining this information throughout thevolume of thick parts.

WEAPONS MATERIALS CHARACTERIZATION

LANSCE studies of the fundamental properties of plutonium and otherweapons materials provide a better understanding of how materialsbehave under the extreme conditions of high-pressure shocks inducedby high-explosives.

For example, studies that investigate the nature of the interatomic bondsthat hold plutonium atoms in their lattice will provide information thatwill be important in developing more sophisticated models of weaponsmaterials behavior. When incorporated into advanced simulation codes,these models will provide the chief means by which safety, performance,and reliability of the aging stockpile is assessed.

HIGH-EXPLOSIVES CHARACTERIZATION

Information guiding the computational modeling of the sensitivity andperformance of pristine, aged, damaged, or remanufactured high explo-sives is crucial for understanding nuclear weapons safety.

LANSCE efforts in this area include two types of experiments: character-izing the microstructure and other materials properties of high explosivesusing well-established neutron scattering methods (but never beforeapplied to high explosives), and employing a new experimental tech-nique called neutron resonance radiography to study temperatures and

11

ÕResearcherRob Robinsonstands atopthe PHAROSinelast icscatter inginstrument,which wi l l beused to studythe characterof p lutonium’sinteratomicbonds.

velocities in the interior of reacting high explosives. This new techniquepromises to be the only feasible way to make accurate measurements inan explosive environment that may exist for only millionths of a second.The very intense, short bursts of low-energy neutrons available atLANSCE are the key to the feasibility of these measurements.

DYNAMIC MATERIALS RESPONSE

Another application of the neutron resonance radiography technique mentioned above is direct investigation of thebehavior of weapons materials under transient high-pressure(for example, shock wave) conditions. This technique pro-vides more information on the behavior of shockedmaterials on a macroscopic scale that is fundamentally morecomplete than has ever before been available.

Studies of this kind complement studies of microscopic prop-erties discussed in “weapons materials characterization,” butthey address the same need for more sophisticated modelingof materials behavior. Work that demonstrates the practi-cality of these measurements is now in progress at LANSCE.

IN CONCLUSION ...

The LANSCE program for stockpile stewardship has made significantadvances toward its research objectives in the year since its inception.Each of the key issues in DOE’s Stockpile Stewardship and ManagementProgram is addressed by one or more of the LANSCE research areas dis-cussed above. These advances would not have been possible without thecollaborative efforts and broad interdisciplinary mix of talent contribut-ed by LANSCE researchers and their colleagues throughout the weaponsresearch community.

The synergism among many elements of the defense, basic, and appliedresearch communities at Los Alamos and elsewhere, particularlyLawrence Livermore National Laboratory in California, has turned thestockpile stewardship ef fort at LANSCE from a vision into agrowing reality.

C O N T A C T : S T E P H E N S T E R B E N Z

L A N S C E S C I E N C E - B A S E D

S T O C K P I L E S T E W A R D S H I P P R O G R A M

( 5 0 5 ) 6 6 7 - 7 2 4 9 • E - M A I L : s t e r b e n z @ l a n l . g o v


12

ÕA high-pressure

cel l forneutron-

scatter ingstudies . Th is

ce l l , which wasdeveloped by

mater ia lssc ient ists in

France, holdsweaponsmater ia ls

samples at h ighstat ic pressures

whi le detectorinstruments

recordneutron-

scatter ing data.

13

TRITIUM PRODUCTION VITALTO LONG-TERM SAFETY AND

RELIABILITY OF NUCLEARWEAPONS STOCKPILE

LOS ALAMOS COLLABORATES

WITH OTHER NATIONAL LABORATORIES

TO DESIGN A SAFE, SIMPLE METHOD

OF TRITIUM PRODUCTION

By 2007, the United States will need a steady and reliable source of tritium to maintain the viability of its nuclear

weapons stockpile. Present tritium requirements are beingmet through the reuse of tritium recovered from dismantlednuclear weapons, but this will not be sufficient for futureneeds. So, the Department of Energy is evaluating twomethods of producing tritium: a reactor-based system and anaccelerator-based system. In December 1995, Secretary of Energy Hazel O’Leary announced thedecision to pursue a “dual-track” strategy, funding development of bothreactor- and accelerator-based systems for tritium production.

The Accelerator Production of Tritium Project, or APT, led by Los Alamos,will build and test critical components of the acceleratorsystem and will par-ticipate in the designof the plant. TheDOE will supportother laboratories inthe development ofreactor-based tritiumtargets and examinethe policy and regula-tory issues associatedwith the purchase of acommercial reactor or irradi-ation services. The most promisingmethod of the two will be implementedas the primary method of tritium production.


13

A cutaway ofthe tr i t ium-product ionfac i l i ty .

Ô

Target Building

Tritium Extraction Facility

Length of Facility = 1.5 km

Cooling Towers for Target Building

Cooling Equipment

Cooling Towers

Accelerator Tunnel

14


Tritium, an isotope of hydrogen, is used to increase the explosive powerof nuclear warheads. Tritium occurs naturally, but rarely, and has aradioactive half-life of 12.3 years. A radioactive half-life is the averagetime required for one-half of any quantity of radioactive atoms toundergo radioactive decay. Although no new weapons are being pro-duced, tritium in stockpiled weapons must be replaced periodically toensure their reliability and performance.

Production of tritium at a quantity sufficient to maintain the nuclearweapons stockpile requires an abundant source of neutrons. The mostefficient way to make neutrons with an accelerator is through a nuclearreaction process called spallation. In spallation, high-energy particlesbombard atoms in a target material, producing neutrons and othersecondary particles.

The source of the high-energy particles in the APT system is the proton-beam injector, located at the front of the accelerator, which ionizeshydrogen atoms to form alow-energy proton beam.Subsequent sections ofthe accelerator graduallyincrease the speed of theprotons. The design of theAPT accelerator calls for alinac that is approximatelyone mile in length andaccelerates a proton beamto 92 percent the speed oflight — about 171,000miles per second.

At the accelerator exit, the beam is expanded to distribute protonsevenly across the face of the target. The expanded proton beam strikes atungsten-and-lead target initiating a spallation process that producesabout 43 neutrons per proton. To form tritium, helium gas captures theneutrons once they have been slowed by heavy water. Tritium producedin the target is extracted continuously and purified at the tritium-extraction facility.

Los Alamos has been studying the advantages of an accelerator-basedtritium production system since the late 1980s. Recently, a teamof Los Alamos-led scientists and engineers from several U.S. nationallaboratories and industry have designed an accelerator-based

ÈResearcher Joe

Shermandemonstrates

how the protonin jector

acceleratesionized

hydrogenatoms to form

a low-energyproton beam.

tritium produc-tion system basedon well-estab-lished, existingtechnology inoperational accel-erators, tritiumextraction, andneutron targets.

The design, com-pleted in late

1994, used expertise from Los Alamos, Brookhaven, LawrenceLivermore, and Sandia national laboratories as well as the industrialcompanies Bechtel, Babcock & Wilcox, Northrop-Grumman, GeneralAtomics, Maxwell Balboa, and Merrick.

The design of an accelerator-based tritium production system is basedon 23 years of operating experience at LANSCE (formerly LAMPF), theLos Alamos high-power linear accelerator, or linac, and its associatedspallation neutron sources.

Accelerators such as LANSCE have demonstrated exceptional perfor-mance under long-term, factory-like conditions, operating 24 hours aday, seven days a week with periodic shutdowns for maintenance.Virtually all APT components have been sufficiently demonstrated toprovide confidence that the plant will operate as designed and produceall the tritium required to supply the stockpile.

Accelerator Production of Tritium has several advantages, the greatest ofwhich is that neutrons are produced in a spallation process (without fis-sile materials) and, therefore, has no chance of a criticality accident.Furthermore, no spent nuclear fuel is generated.

The system can be shut off almost instantaneously, and once shut down,does not generate neutrons. Tritium is extracted constantly from theproduction area in the APT system, preventing buildup of tritium as inreactors, and thus greatly reducing the possibility of a release of radioac-tivity into the environment.

Although nuclear reactors can also be used to produce tritium,accelerator-based technology does not jeopardize the long-standingUnited States practice of separating the use of commercial nuclear powerequipment from military material production.

15


ÈMore than 50

industry leadersrecent ly toured

the protonaccelerator atLANSCE after

they werebr iefed on

us ing anaccelerator to

produce tr i t iumfor the nat ion’s

nuclearweapons

stockpi le . Fromleft to r ight areDwayne Wi lson,

F luor Danie lInc. ; Robert

Tauss ig, Bechte lNat ional Inc. ;

and J im Stova l lof Los A lamos.

16

To ensure that APT can be built on schedule and on budget, Los Alamosis assembling a low-energy demonstration accelerator to verify long-term performance. Scientists will demonstrate the production efficiencyof APT with prototype targets using a low-power beam at LANSCE.

Participation in the technology demonstration as well as plant designand construction will be done by a prime contractor who will beselected by the DOE late this summer. If the DOE selects APT, theSavannah River Site in South Carolina will be the preferred location for atritium production plant because of its long-standing expertise andcapability in handling tritium.

Total cost for the project — estimated in 1995 — is approximately $2.9billion. Annual operating costs are estimated at $120 million to $200million, depending on the cost of electricity.

Accelerator Production of Tritium is a safe, environmentally benignmethod of producing tritium to ensure the viability of our nuclearweapons stockpile.

C O N T A C T : P A U L L I S O W S K I

A C C E L E R A T O R P R O D U C T I O N O F T R I T I U M

( 5 0 5 ) 6 6 7 - 7 1 0 6 • E - M A I L : l i s o w s k i @ l a n l . g o v

w o r l d w i d e w e b a d d r e s s :

h t t p : / / w w w . a t d i v . l a n l . g o v / d o c / a p t


ÈResearcher

Dave Hodgkinsmakes a minoradjustment to

the protonin jector . Th is i sa prototype ofthe in jector to

be bui l t for theLow-Energy

Demonstrat ionAccelerator at

Los Alamos.

17


WHAT IS TRITIUM?

T ritium is a radioactive form of hydrogen that ismade naturally in small amounts in the atmosphere.

It also can be made artificially in any quantity forpurposes ranging from medical to military.Tritium generates a weak type of radiation known as beta emission.Beta particles cannot penetrate clothing or skin; however, bybreathing in water-vapor containing traces of tritium, or by eatingor drinking tritium-contaminated food or water, tritium can be aserious health hazard — even lethal in extremely large doses.

Tritium has a biological half-life of approximately 10 days, whichmeans if a person ingests tritium, it takes the body approximately

10 days to rid itself of half the amount ingested.Tritium’s weak radiation and 10-day

biological half-life make it an importanttracer for studying biological processesor testing the effectiveness of new phar-maceutical drugs.

Cosmic rays produce some tritium inthe upper levels of the atmosphere, andrainwater is usually found to containminute amounts of tritium.

Tritium has a radiological half-life ofapproximately 12.3 years — the average time

required for one-half of any quantity of radioac-tive atoms to undergo radioactive decay into a stable orless-radioactive daughter product.

Tritium production for defense applications requires either a nucle-ar reactor or an accelerator. Both systems produce neutrons, whichare then captured by lithium or helium atoms, converting them totritium. The Department of Energy is currently evaluating bothsystems as a potential future source of tritium.

+

—

ÕA tr i t ium atom

is composed ofa nucleus

conta in ing oneproton and two

neutrons andone orbit ing

electron.

18


LOS ALAMOS APPROACHELIMINATES NUCLEAR WASTE

TRANSMUTATION PROCESS TRANSFORMS

LONG-LIVED RADIOACTIVE MATERIALS

INTO SHORT-LIVED MATERIALS

A Los Alamos approach to reduce the long-term hazards and storage requirements of radioactive nuclear

waste could solve one of the world’s most pressingenvironmental problems.More than 1,000 tons of plutonium exist today in the spent fuel of theworld’s nuclear reactors. An additional 80 tons are added each year fromthe same reactors. The inventory of plutonium already separated fromreprocessed spent fuel is more than 130 tons and steadily growing, andplutonium from dismantled nuclear warheads is now contributing tothis large excess.

Los Alamos researchers are developing an accelerator-driven transmuta-tion technology that bombards nuclear wastes with neutrons andtransmutes them into stable or short-lived products. This proceduretransforms radioactive materials into a form that allows cheaper andsafer disposal.

Current plans for high-level waste generated by nuclear reactors andnuclear weapons research and development are to store it in isolation fortens of thousands of years until its radioactivity decays to safe levels. In1987, Congress selected Yucca Mountain, Nev., as the nation’s first sitefor the geological storage of high-level nuclear waste. The Los AlamosAccelerator-Driven Transmutation of Waste concept offers a potentialalternative to the geological storage of nuclear waste.

The Los Alamos transmutation concept beginswith an accelerator that directs medium-energyprotons (1,000 million electron volts) onto atarget of liquid lead. Each proton creates an ener-getic spray of about 30 neutrons. The target issurrounded with molten salts, such as lithium andberyllium fluoride, which contain less than .1 per-cent of actinides such as plutonium. Whenlong-lived radionuclides, including plutonium,

Spent fuel rodsfrom nuclearreactors , suchas thosepictured below,must s i t instorage forthousands ofyears . The LosAlamos wastetransmutat ionsystem wouldel iminate theneed formanagedstorage of fuelrods and otherhigh- leve lnuclear waste.

Ô

americium, neptunium, technetium, and iodine absorb a neutron theytransmute into nuclides that are not radioactive or into nuclides whoseradioactivity decays much faster, thus eliminating the need for protectedstorage beyond a few hundred years. Transmuting to short-livednuclides is an important advantage because it is much easier to engineerand guarantee a containing structure for this shorter time frame.

The intense fluxes of slow neutrons allow high transmutation rates withmodest waste inventories. As the system converts the waste into stableor short-lived radioactive elements, chemical-separation processes continuously remove undesirable neutron-absorbing products. The heatproduced in the transmutation process can be converted efficiently intoelectrical energy — about five times the electrical energy required topower the accelerator. (See related article in this issue of

Dateline.)

The power of a typical linear accelerator designed for large-scale wastetransmutation would be roughly 50 times greater than the existing LosAlamos accelerator. Producing the required accelerator is considered arelatively straightforward extension of today’s technology.

The U.S. nuclear power industry currently practices a “once-through”fuel cycle. Once the spent fuel is removed from a reactor it must bestored virtually forever. Other nations reprocess the fuel by removing theplutonium and recycling it into new reactor fuel rods. President JimmyCarter rejected the reprocessing method in 1977 because it concentratesplutonium into a form that can be extracted and used for nuclearweapons. There is still no large-scale reprocessing done in the UnitedStates and more than 28,000 metric tons of spent fuel reside in holdingpools at U.S. nuclear reactor sites.

In the short term, unreprocessed spent fuel is relatively inaccessible toterrorists because it is mixed with highly radioactive fission products.But over the long term, large and growing quantities of this spent fuel,the spread of plutonium separation technology, and the gradual reduc-tion in radioactivity from the fission products will make the plutoniumcontained in spent fuel increasingly accessible.

Reducing the inventory of plutonium and other fissile materials makesthem easier to safeguard and diminishes the likelihood the materials willbe diverted for weapons use.

The accelerator-driven transmutation technology is a robust, efficient,and complete waste-treatment system. The robustness of the subcriticalaccelerator-transmutation system allows it to accept a wide range of

19


nuclear waste, from defense spent fuel and scrap plutonium to commer-cial spent fuel. No plutonium-breeding material, such as uranium, isexposed to the neutron flux.

The system will transmute plutonium and most other components ofnuclear waste efficiently because the transmuter needs only a smallinventory of radioactive materials to operate. The system will operate toa high degree of completeness, leaving little untreated waste for long-term storage and reducing the potential hazard of any waste that isstored by eliminating its long-lived radioisotopes and chemically mobilefission products.

After a successful development and demonstration period, accelerator-driven transmutation technology will be available to transmute, over afew decades, the hundreds of tons of plutonium accumulated inworldwide inventories. An aggressive effort to develop and demonstratethe transmutation technology could see the first full-scale plant inoperation by 2010.

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Power system Converts steam heat into electricity (10 to 20 percent of generated electricity is returned to the accelerator)

Target Protons striking target produce

spallation neutrons

Blanket Neutrons are multiplied in

the surrounding fissionable fuel (circulating molten salt)

Accelerator Delivers ~1,000 MeV

proton beam to target

Waste feed Robust processing of actinide and

fission product waste

Waste stream Small quantity of short-lived fission

products to engineered storage

Actinides, long-lived fission products

Power recycled to accelerator (100 megawatt)

Power to the grid (1,000 megawatt)

ATW Separations

Fission Product Removal

ÕThe Accelerator

Transmutat ionof Waste, or

ATW, process.

21


RUSSIANS COLLABORATE

WITH LOS ALAMOS ON

ACCELERATOR TRANSMUTATION OF WASTE

More than 300 weapons scientists from the former Soviet Union are cooperating with Los Alamos

researchers on the development of AcceleratorTransmutation of Waste.

Los Alamos researchers anticipate that theirRussian counterparts will contribute a great dealto the success of the ATW program because of theRussians’ highly specialized skills and their desireto redirect their efforts from weapons design to thechallenging problems related to the handling andelimination of nuclear waste. The collaborativeeffort, known as Project 17, is sponsored by theIndustrial Science and Technology Center.

Russian participation in the Laboratory’s ATW effort began inOctober 1993. Guidelines for Project 17 were laid out in Moscowat the Institute of Theoretical and Experimental Physics during aconference on transmutation technology. The Russian laboratoriesof Chelyabinsk, Arzamas-16, Obninsk,Kurchatov, and the Institute ofTheoretical and Experimental Physicshave been prominent in the Project 17collaboration. Project activities haveranged from theory and system studiesto experimental nuclear physics andengineering.

The ISTC will fund some new ATW-related projects beginning thisOctober. These projects include the study of liquid lead targets at theInstitute of Power Physics and Engineering in Obninsk, the study ofvolatile extraction from molten salt systems at Kurchatov, presentlynot available nuclear cross-section measurements of fission productsat Arzamas-16, innovative blanket design and large-scale molten saltloops at Chelyabinsk, and accelerator design at Yerevan, Armenia.

ÕLos A lamos

sc ient istsChar les

Bowman, HarryDewey, and EdArthur jo in Dr .

K ise lev, deputydirector of

ITEP, intoast ing the

future ofProject 17dur ing the

seminalNovember 1993

Transmutat ionConference in

Moscow.ÕThe Russ iandes ign groupfromChelyabinsk atwork on theATW projectshort ly afterProject 17 wasin it iated.

22

ACCELERATOR-DRIVENENERGY PRODUCTION

ELECTRICITY FOR THE FUTURE

CAN BE PRODUCED WITHOUT SIGNIFICANT

GENERATION OF WASTE

S cientists envision that the Los Alamos Accelerator Transmutation of Waste concept will not only

destroy materials that pose hazards to both world peaceand the environment, it will produce a safe, clean, andeconomic source of electricity.Because of its versatility, the accelerator transmutation technologydescribed in the previous article will be able to produce electricity asefficiently as today’s nuclear reactors by using thorium once thesupply of nuclear waste and spent fuel is exhausted. Thorium is areadily available natural element that exists in nearly limitless supply.

The thorium-based transmutation system generates virtually noplutonium and a negligible amount of waste that will notrequire management for thousands of years. The system willdestroy its own long-lived fission products.

The system is safe because the thorium-based Accelerator-Driven Energy Producing system, or ADEP, unlike a nuclearreactor, contains too little fissile material to sustain a chain reac-tion and a supply of enriched fuel is not needed because thesystem itself generates the extra neutrons necessary for the tho-rium cycle to perform efficiently.


By addingthor ium, ATWbecomes ADEP,a safe,eff ic ient ,minimal lypol lut ingenergyproduct ionsystem.

Ô

Waste stream Small quantity of short-lived fission

products to engineered storage

Power system Converts steam heat into electricity (10 to 20 percent of generated electricity is returned to the accelerator)

Target Protons striking target produce

spallation neutrons

Blanket Neutrons are multiplied in

the surrounding fissionable fuel (circulating molten salt)

Accelerator Delivers ~1,000 MeV

proton beam to target

Power recycled to accelerator (100 megawatt)

Power to the grid (1,000 megawatt)

Long-lived fission products

ADEP Separations

THORIUM FEED

23

As in the waste-burning Accelerator Transmutation of Wastesystem, the process begins with an accelerator-generated source ofneutrons surrounded by an assembly consisting of a graphite mod-erator and a fuel that produces energy through fission. The fuel isembodied in the coolant — a lithium-beryllium-fluoride moltensalt — to ensure a high-temperature, high-efficiency operation.The net power produced is five times that needed to drivethe accelerator.

The system will constitute a major advance in technology fromtoday’s reactors. First, the assembly is subcritical and cannot sus-tain a chain reaction without the accelerator beam on. (Switch thebeam “off” and the power drops instantly.) Second, the systemgenerates no significant amounts of plutonium and the heat energycomes from the transmutation processes. The heat is then used toproduce steam, which powers a turbine to produce electricity.

Thorium exists in sufficient quantities to support future worldwideelectrical needs many times greater than today’s for thousands ofyears. Thorium-producing mines are located in the United States,Brazil, the former Soviet Union, China, India, and Australia.Thorium also is used to manufacture sun lamps, incandescentlighting, medicines, ceramics, and electrodes.

A single truckload of thorium would be enough to power anaccelerator-driven energy system for its projected lifetime of 30 to40 years. A single accelerator-driven system could provide powerto a city of more than half a million people.

The worldwide consumption of electricity is expected to increase50 to 75 percent by 2020, according to the World Energy Council.Accelerator-Driven Energy Production from plutonium, spentfuel waste, and ultimately thorium could be a reality within thenext 15 years.

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ACCELERATOR-DR IVEN TRANSMUTAT ION TECHNOLOGY

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NEUTRON SCATTERING GIVESRESEARCHERS A PEEK INSIDE

ADVANCED MATERIALSTECHNOLOGY MAKES POSSIBLE

NONDESTRUCTIVE TESTING ON A WIDE VARIETY

OF INDUSTRIAL PRODUCTS

To design improved materials for industrial applications, scientists build on their understanding of existing

materials, a large part of which comes from informationabout their structures. Neutron scattering can provide thatinformation, often in situations where other techniques fail.

Successful neutron-scattering experiments require anintense source of neutrons to be directed at a samplebecause only a small fraction of the neutrons are scat-tered; the rest pass through the sample without beingscattered or absorbed. At certain energies neutrons canpenetrate solids and liquids up to 10,000 times moreeffectively than X-rays. Their neutrality and the weak-ness of their interactions with matter allow neutrons toprovide information about a material’s bulk, as opposedto its surface structure, and they do so nondestructively.

Neutron scattering is a proven tool for uncovering residual stresses thatcan be induced in materials during fabrication or in components afterservice. The consequences of residual stresses can be devastating, rang-ing from the unexpected failure of critical engineering components tothe cracking of railroad tracks leading to train wrecks. Other techniquesexist for identifying residual stress, but in many cases neutron scatteringis the only nondestructive way of spotting and measuring the stress deepin the interior of engineering materials.

Since the 1950s, the origins of residual stress have been investigated andmeasured extensively to understand how they cause failures and howthey can be prevented or controlled. It is easy to see gross changes inmetal or plastic when a heavy load causes them to buckle or stretch. Butresidual stresses cannot be seen with the naked eye or measured directly.Neutron scattering gives researchers a way to understand the changes atthe atomic level that result from applied stress. At the Manuel Lujan Jr.

24


ÕJohn Thomas

( left ) andJoyce Roberts(center ) work

with Hans-RudiWenk, a user

from theUnivers i ty ofCa l i fornia atBerke ley, toprepare icesamples for

textura lstudies .

25

Neutron Scattering Center, Los Alamos researchers are working in a vari-ety of programs with industry and academia to develop the relatively newtool of pulsed neutron scattering — a tool that provides a unique, nonde-structive method of measurement for a range of advanced materials.

For example, there is currently considerable interest in the automobileand aerospace industries in using composite or heterogeneous materialsfor stronger, lighter engine parts because they offer increased fuel efficiency and reliability. However, because composites consist of two or more materials mixed intimately, they are difficult to study usingconventional methods.

Because of their penetrative strength and ability to distinguish betweendifferent materials, neutrons have proved an invaluable aid in under-standing the performance of new materials. Recently, Los Alamosscientists collaborated with researchers from General Electric to measureresidual stresses in one such composite. The material, titanium rein-forced with continuous fibers of silicon carbide, is intended for use inhigh-temperature regions of jet engines. Its performance in this demand-ing environment depends strongly on the residual strains that crop upwherever the two materials interface.

In a similar study, Los Alamos scientists recently worked with aresearcher from the Massachusetts Institute of Technology to studymicrostructural changes in a pellet-sized sample of nickel-titanium whenthe sample was loaded with 11,000 pounds. The researchers studied thereversible atomic re-orientation between two crystalline structures —austenite and martensite. The reversible action is an effect called “shapememory” and is desirable in products such as eyeglass frames: In theevent the frames are bent, they pop back to their original shape.

Although the scientists knew that nickel-titanium possessed the property of shape memory, neutron-scattering technology revealed the actual atomic transformations that occurred when a load was appliedto a sample. The knowledge will help scientists find away to stiffen nickel-titanium by reinforcing it withanother material without sacrificing any shape memoryin the process. This type of reinforced composite wouldbe desirable in products that would benefit from shapememory but require more stiffness than that exhibited by the relatively low strength of the pure nickel-titanium material.


Mark Bourkeprepares ahigh-temperaturestress test . At LANSCEsc ient ists usethe stress r igto measurestra in — aneffect of stress — in eachconst i tuent ofa compositemater ia ls imultaneous ly .Measurementsare made underboth appl iedstress and h ightemperature.

Ô

Another aspect of residual strain research allows the measure-ment of strains at different positions inside deformed

objects. For example, these strains are prevalent in steampipes or pressure vessels which typically contain residualstresses from bending and welding during fabrication. Inmany cases these components are subjected to steadyloading at elevated temperatures.

To predict the lifetime of this type of equipment in high-temperature environments such as electric power or

chemical processing plants, manufacturers need to predictthe rate of growth of any defects: a rate that depends on the pres-

ence of residual stress.

Los Alamos researchers in collaboration with scientists from theImperial College in London used neutron scattering to examine howresidual stresses evolve in a steel alloy used to make steam pipes. Theirmeasurements will help manufacturers determine to what extent thesestresses influence component lifetimes.

In polymer research, neutron-scattering techniques help scientistsunderstand a polymer’s behavior by providing the data needed to con-struct structural models of different materials and their interactions witheach other.

Polymers are chains of repeating molecules that have a variety of materi-al and biochemical applications. Although polymers are common ineveryday products such as plastic containers and the nonstick coatingon metal cookware, some fundamental questions remain as to how theyinteract with solvents and other materials and how they actually modifysurface properties.

In a collaboration between Los Alamos and Sandia National Laboratoriesof Albuquerque, researchers investigated ways of enhancing the adhe-sion between copper and epoxy, a type of bonding common to circuitboards found in television sets, computers, even nuclear weapons. Anybreakdown in the mechanical bonding between materials can have dev-astating effects on a component’s reliability.

The researchers examined the feasibility of using special co-polymers tostrengthen the chemical bridges between the two materials. Aco-polymer is composed of two different types of polymers. In thisexample, one of the co-polymer’s free ends formed a chemical bond withcopper, while the other preferred to mix with epoxy.

26


ÕMedic ine

encapsulated inthe center ofth is polymerstays in the

body longer,increas ing theprobabi l i ty of

i t be ingabsorbed,

rather thanshed. Neutron-

scatter ingmeasurements

a l lowresearchers todetermine the

exact structureof polymers.

The researchers determined that by dipping a copper-coated siliconwafer in a polymer solution containing a weak solvent, they could orientthe co-polymer molecules to ensure that the copper-binding end camein contact with the copper film. This orientation strengthened the bond-ing between the the copper film and the polymer. These results are thefirst step in developing circuit boards with better material-to-material adhesion.

The pharmaceutical industry is interested in using polymers as vehicles totransport drugs through the body. By encapsulating medicine in a struc-ture that resembles a human cell decorated with hairy polymer arms, themedicine remains in the body for days rather than hours, thus increasingthe probability it will be absorbed, not shed. By adding a sugar or a proteinto the polymer’s outer surface, it can be broken down by one type of celland remain impenetrable to all others. This built-in specificity allowsresearchers to design drugs that treat disease sites such as tumors, withoutaffecting the body’s normal tissue.

Neutron scattering measurements make it possible for researchers tomodel the molecular structure of co-polymers. The models then helpthem design more effective drug therapies and predict adrug’s consequences on the human body.

During the past decade, neutron-scattering techniquesalso have revealed the structure of the first high-temperature superconductors; the structure ofbuckminsterfullerenes, or bucky balls; the conforma-tion of molecules in a polymer melt; the interfacialstructure of artificially produced polymeric and mag-netic layers; the spin dynamics of highly correlatedelectron systems; and the condensate fraction in superfluid helium, among others.

The Lujan Center provides neutron beams with a higher peak intensitythan any other facility in the world, allowing scientists to perform exper-iments more quickly and on smaller samples. As more neutronspectrometers are added and the annual operating time is increased overthe next few years, the Lujan Center has the potential to become theworld’s most productive pulsed-spallation source.

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Greg Smithplaces acopper-epoxysample in apolymer bath.The polymerstrengthens thechemica l andmechanica lbonds betweencopper andepoxy — af inding that wi l lhe lp sc ient istsimprove there l iab i l i ty ofc i rcuit boards.

Ô

28

NEUTRON STUDIES REVEALTHE STRUCTURE OF

A NEW TYPE OFCHEMICAL COMPOUND

DISCOVERY COULD LEAD TO NEW, CHEAPER,

MORE-EFFECTIVE CHEMICAL CATALYSTS

N eutron scattering is effective in determining the structure and dynamics of new chemical

compounds and catalysts. In a particular example, LosAlamos chemist Gregory Kubas and physicist JuergenEckert used the technique to discover a new kind ofchemical bonding — the stable hydrogen-metalcomplex — that has revolutionized the way chemistsperceive how catalytic hydrogenation works. Kubas was studying the effectivenessof various transition metals, such asmolybdenum and tungsten, in catalyz-ing the conversion of sulfur dioxide,an atmospheric pollutant, into benignelemental sulfur. In the process, herealized that the product of one ofthese reactions contained a moleculeof hydrogen bound to an atom of thetransition metal.

Prior to Kubas’ study, scientists gener-ally believed that a hydrogen moleculecould not bind to another atom, butwould always split into two separatehydrogen atoms before undergoing a chemical reaction. Kubasproved that a stable hydrogen-metal molecule can exist undernormal laboratory conditions. The structure of one of the newcompounds was definitively demonstrated by the use of neutron-diffraction technology in collaboration with Los Alamos chemistPhil Vergamini.


Neutronscatter ingtechnologya l lowed GregKubas ( r ight )and JuergenEckert todetermine thestructure of astablehydrogen-meta lmoleculeinvolved incata lyt ichydrogenat ion.

Ô

29


This discovery was recognized as one of the most important find-ings in chemistry in the 1980s and has spawned related work inmore than 50 research groups worldwide.

Eckert later probed the propeller-like rotation of the hydrogenmolecule bound to the side of the metal atom with inelastic neu-tron scattering. His work proved a crucial chemical bonding forcethat both stabilizes the hydrogen molecule’s bond to the metal andpromotes the chemical reactivity of hydrogen. This so-called“activation,” or weakening, of the strong hydrogen-to-hydrogenbond also applies to other chemical bonds such as the carbon-to-hydrogen bond in hydrocarbons.

One of the “holy grails” in chemistry is selectively transforming themethane in abundant natural gas to liquid fuels such as gasoline ormethanol. Kubas’ hydrogen-metal complex recently has beenfound to bind and activate the silicon-hydrogen bond in silane(SiH4), a close relative of methane. Neutron studies of these com-pounds are in progress.

Because some evidence exists that metal-bound hydrogen andrelated molecules are directly involved in chemical catalysis, thediscovery could lead scientists to new, cheaper, and more-effectivechemical catalysts than those presently used in research and indus-try. Hydrogen is used in the largest volume commercial chemicalreactions in the world, such as in crude-oil refining to removesulfur and also to produce 10 billion tons of ammonia per yearfor fertilizers.

Although present catalysts are effective, the enormous volume ofsuch reactions means any small improvement could translate intolarge savings in cost. Ammonia production is particularly energyintensive, and scientists have for decades looked to find a moreefficient way of making it. The studies of how small moleculessuch as hydrogen are activated on metals could lead to a solutionfor this problem.

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FUNDAMENTAL LIFEPROCESSES INVESTIGATED

WITH NEUTRON SCATTERINGEXPERIMENTS YIELD PRECISE

THREE-DIMENSIONAL MOLECULAR MODELS

Many of the techniques and areas of expertise applicable to research on nuclear weapons are also applicable to

research on structural biology. Neutron scattering is onesuch technique. When combined with other advancedlaboratory techniques such as stable-isotope labeling,neutron scattering gives scientists a way of obtaining precisethree-dimensional pictures of important chemical structures.Because in nature form usually follows function,understanding the architecture of a biological molecule isthe key to understanding how the molecule functions. Some of the most significant experiments to date have focused onmolecules involved in biochemical regulation. People rarely give muchthought to the complex biochemical processes behind simple actionssuch as blinking an eyelid or lifting a glass. But one of the key issues inbiochemistry is the question of how reactions are switched on and off oraccelerated and decelerated in different types of cells, at different stagesof development, and in response to external and internal signals.

30


J i l l Trewhel laa l igns the X-raybeam on thesmal l -angle X-ray scatter inginstrument.Researchers usethe instrumentto obta ininformat ion onthe overa l lshape of amolecule andto ident i fy thesolut ioncondit ionsthat wi l l g ivethe bestsmal l -angleneutron-scatter ingmeasurements.

Ó

Scientists already know thata breakdown in the regula-tion of these chemicalprocesses can lead to diseaseor death; but to developtreatments and cures to fixthe problems, they mustfirst understand how theprocesses work.

The key to understandingbiochemical processes lies ina complex network ofchemical messengers, trans-mitters, and receivers thatorchestrate the time andrates of reactions in responseto physiological stimuli.

One of the simplest messengers involved in biochemical regulation isthe doubly charged calcium ion, Ca2+. Calcium typically binds to anumber of different receptor proteins, the most ubiquitous of which iscalmodulin. The resulting calcium-calmodulin complex then binds toand activates one of a number of different enzymes. These targetenzymes are involved in a variety of biological functions, includingmuscle contraction, neurotransmitter release, and generation ofmetabolic energy from glycogen.

Neutron-scattering experiments at Los Alamos helped researchersunderstand how one macromolecule, the calcium-calmodulin complex,manages to regulate such a number of diverse enzymes. The sites on thetarget enzymes to which the calcium-calmodulin binds are aschemically diverse as the enzymes are functionally diverse. So, whilecalcium-calmodulin is the key that unlocks the actions of a variety ofenzymes, the locks vary on each enzyme.

The Los Alamos researchers knew from previous studies by other scien-tists that the calmodulin protein had an unusual dumbbell-shapedstructure with two football-shaped ends interconnected by a helicalregion. Two calcium binding sites exist on each of the dumbbell’s ends.

Neutron scattering experiments allowed the researchers to observecalcium-calmodulin acting on a number of target enzymes and identifytwo general types of interaction.

31


ÈLos A lamos

researchersBr ian

MacDonald( left ) and Roy

Nie lsen preparefor X-ray

scatter ingexper iments at

the computerdata stat ion.

In the most common interaction, the helical region flexes so that thedumbbell collapses around a target enzyme. Imagine a person bendingover and wrapping his arms around a bulky load. Just as a person canlift many types of loads, the flexibility of the helical region allows themolecule to collapse around different types of enzymes with differentchemical surfaces.

In the other type of interaction, the calmodulin retains its dumbbellshape with the helical region of the macromolecule still extended whenit binds to a target enzyme. The flexibility of the helical region allowsthis single molecule to accommodate diverse enzyme targets, while theconstant chemical surface of the protein, which is independent of theoverall conformation, programs specificity into the structure by requir-ing certain complementary features in the target.

Another protein, troponin C, resembles calmodulin in structure, but hasthe highly specialized function of triggering muscle contraction. LosAlamos researchers recently were able to elucidate the structure of thecomplex of troponin C with its regulatory target troponin I, whichtogether serve as a switch for coordinated muscle action.

Each muscle cell contains bundles of thick and thin filaments. As themuscle contracts or relaxes, these filaments slide past each other.Researchers already knew that the movement of these filaments is regu-lated by a pair of protein molecules, troponin C and troponin I, thatrespond to the presence or absence of calcium. But until the Los Alamosresearchers studied the problem, no one had a good model of how thisprotein pair did its job.

To discover how the protein molecules are linked and see how theyinteract, the researchers used neutron scattering and a stable-isotopelabeling technique that substitutes deuterium for hydrogen. Deuteriumis a heavier form of hydrogen whose atoms have an additional protonand neutron. The number of neutrons in an atom makes a fundamentaldifference as to how the neutrons scatter, so a molecule labeled withdeuterium casts a distinct neutron shadow.

The researchers found that when calcium binds to troponin C, which isat all times locked into the muscle fibers, the troponin I molecule(which inhibits muscle action in the absence of calcium) is wrappedaround and anchored to troponin C. In this form, the troponin complextriggers the formation of a protein bridge between the thick and thinfilaments of the muscle cell.

32


The bridgeworks like alever to slide thethick and thinfilaments pasteach other, caus-ing the muscleto contract.When calcium isremoved, tro-ponin C releasesits hold on tro-ponin I, which then is free to bind to its alternate thin filament site, thusrestoring its inhibitory function, and the muscle relaxes.

This reversible action happens at multiple sites on every filamentin a cell simultaneously and there are hundreds of filaments in eachmuscle cell. When the muscle cells respond to the calcium switch inharmony, your eyelid blinks or your fingers grasp the paper. A papersummarizing this research appeared in the December 1994 issue of thejournal Biochemistry.

The Los Alamos research on biochemical regulators may not lead to newtreatments or cures in the short term, but it helps researchers under-stand the molecular basis for diseases, specifically those that are thedirect result of a breakdown in biochemical regulation.

Neutron-scattering experiments have been carried out at theLaboratory’s accelerator complex on a number of macromolecules insolution, including the complexes formed by antibodies and theforeign substances they target for elimination; chromatin, the structuralfabric of DNA, and certain proteins that modulate the accessibility ofgenetic material to replication and transcription; complexes ofDNA with other proteins; and viruses. All of the studies enabledresearchers to obtain structural information about individual compo-nents of the macromolecules.

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ÓGr ise ldaHernandezprepares abio logica lsample for aneutronscatter ingexper iment.

A FUTURE OF NEUTRONSPOWERFUL NEUTRON SOURCE

SUPPORTS BASIC AND APPLIED RESEARCH

Every successful shopping center has as its anchor a large department store to draw in crowds of shoppers.

Without a Neiman Marcus or a Saks Fifth Avenue, centers ormalls are reduced to a smorgasbord of specialty stores thatserves only a small, select group of customers. While a retailcenter is a far cry from a scientific research laboratory, LosAlamos’ most important “anchor store” may soon be the LosAlamos Neutron Science Center, or LANSCE.

With LANSCE, Los Alamos can become theU.S. center for the development and use ofspallation neutron sources for defense,research, and commercial applications. As

other articles in this issue describe, the laboratory already has powerfulsources that produce short pulses of neutrons. In addition, the Laboratoryis in the enviable position of having a powerful enough accelerator to beable to build a new neutron source — referred to as a long-pulse spallationsource — that will complement the existing short-pulse capabilities andposition the United States as a leader in neutron research. The new sourcecan be built relatively quickly and with little technical risk.

Neutron science has contributed to many advanced technologies andprovides basic knowledge that underpins U.S. economic competitive-ness in vitally important industrial sectors such as automotive,aerospace, electronics, biotechnology, pharmaceuticals, materials, chem-icals, and petrochemicals.

Since its beginning in 1987, the Manuel Lujan Jr. Neutron ScatteringCenter at Los Alamos has been open to scientists from industry,academia, and other national laboratories. The Lujan Center has madeits share of scientific contributions, some of which are covered in thisissue of Dateline. However, despite the successes and importance ofneutron-scattering technology to basic and applied research, the UnitedStates has not kept pace with Europe in nurturing neutron-scatteringprograms. At present, the most productive program exists at the InstitutLaue-Langevin reactor in Grenoble, France.

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Los Alamos Neutron Science Center


The establishment of a long-pulse spallation neutron source at LANSCEtogether with the short-pulse spallation source already there will provideneutrons over a uniquely large range of energies for probing all kinds ofmaterials. The proposed long-pulsed source will have 1 megawatt ofpower — more than 16 times the 60-kilowatt power of the Laboratory’scurrent short-pulse spallation source. However, the most importantaspect of the source will be its long pulses of neutrons, which are ideallysuited for research using low energy, or “cold,” neutrons. In contrast, theshort neutron pulses already generated at the Lujan Center are best formaterials research with more energetic, or “hot,” neutrons. The twosources are complementary because each excels for a different type ofscientific research.

Hot neutrons have short wavelengths and are used to probe the dis-tances between neighboring atoms in materials. Changes that occur inthese distances when, for example, a material is stretched or compressedcan give engineers insights into the way the material may fail in use.Cold neutrons with their longer wavelengths probe the larger features insolid materials. In this context, large means many times the distancebetween neighboring atoms but still much smaller than can be seen withan optical microscope. Polymer molecules, which consist predominantlyof chains of carbon and hydrogen atoms, and molecules of biologicalimportance, such as proteins, can be examined using cold neutrons.

For material studies that use cold neutrons, the proposed long-pulsesource will have the potential to perform neutron-scattering experimentsas much as four times more quickly than the world’s current best sourcefor this purpose: the nuclear reactor at the Institut Laue Langevin. Insome cases, the superior performance of the long-pulse source will makepossible experiments that otherwise could not be done.

In addition to neutron scattering, the proposed long-pulse source willprovide excellent capabilities for radiography, a technique used in thesurveillance of nuclear weapons. For this reason, both the basic researchand defense communities stand to benefit from the long-pulse spallationneutron source.

Los Alamos is working with the Department of Energy to devise a fund-ing strategy for construction of a long-pulse source at LANSCE.

C O N T A C T : D A N W E I N A C H T

L A N S C E A N D E N E R G Y R E S E A R C H P R O G R A M S

( 5 0 5 ) 6 6 7 - 3 5 2 5 • E - M A I L : w e i n a c h t @ l a n l . g o v

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Nonprofit Organization U.S. Postage Paid

Los Alamos, NM Permit No.107



Nonprofit Organization U.S. Postage Paid

Los Alamos, NM Permit No.107


BRIEFLY …

The Los Alamos Neutron Science Center is a national facility for defense, basic, and industrial researchavailable for use by members of the world’s scientific community. At the heart of LANSCE is a half-mile-long linear accelerator that provides intense beams of protons with energies up to 800,000,000 electronvolts. Scientists submit proposals to use LANSCE by completing a simple application form found on theworld wide web. Approval is based on advice from program advisory committees that examine the scien-tific merit of proposed basic research and the relevance of defense research to stewardship of the nation’snuclear stockpile. In the past, the LANSCE accelerator produced beams for experimentation for about fourmonths out of the year, but upgrades now under way will permit five months of operation in 1996, sixmonths in 1997, and eight months per year from 1998. Fifty to 100 users a month conduct experiments atLANSCE on topics ranging from strain in engineered components to irradiation of electronic componentsof high-flying aircraft. For more information about the LANSCE users’ program, call Amy Longshore at505-665-5353, send e-mail to [email protected], or see the LANSCE home page onthe world wide web (http://www.lansce.lanl.gov).

LALP-96-1-3/4

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IN THIS ISSUE:

ACCELERATOR TECHNOLOGY INLINE WITH NATIONAL INTERESTS

P A G E 1

A HISTORY OF ACCELERATORS

AT LOS ALAMOSP A G E 5

LANSCE LAUNCHES RESEARCH

CRITICAL TO

STOCKPILE STEWARDSHIPP A G E 9

TRITIUM PRODUCTION VITAL TO

LONG-TERM SAFETY AND

RELIABILITY OF NUCLEAR

WEAPONS STOCKPILEP A G E 1 3

LOS ALAMOS APPROACH

ELIMINATES NUCLEAR WASTEP A G E 1 8

NEUTRON SCATTERING GIVES

RESEARCHERS A PEEK INSIDE

ADVANCED MATERIALSP A G E 2 4

FUNDAMENTAL LIFE

PROCESSES INVESTIGATED WITH

NEUTRON SCATTERINGP A G E 3 0

A FUTURE OF NEUTRONSP A G E 3 4

accelerator technology in line with national interests

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