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ARGONNE NATIONAL LABORATORY

P. O. Box 299 Lemont , Illinois

PHYSICS DIVISION

SUMMARY REPORT

April through June, 1957

Louis A. T u r n e r , Division Direc tor

August , 1957

Preced ing Quar te r ly Repor t s :

ANL-5609 - Apr i l through August , 1956 ANL-5667 - September through December , 1956 ANL-5698 - January through March , 1957

Opera ted by The Universi ty of Chicago under

Contract "W-31-109-eng-38

ANL-5754

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency Thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.

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FOREWORD

This Summary Report on the work of the Phys ics Division of the Argonne National Labora to ry is p resen ted for the information of nnembers of the Division and a l imited number of other persons in te res ted in the p r o g r e s s of the work.

It is mere ly an informal p r o g r e s s r epo r t . The r e su l t s and data therefore must be understood to be p re l imina ry and tentat ive.

The i s suance of these r e p o r t s is not intended to consti tute publication in any sense of the word. Final r e su l t s ei ther will be submit ted for publ ication in regula r profess ional journa ls o r , in specia l c a s e s , will be p resen ted in ANL Topical Repor ts .

TABLE OF CONTENTS

TEt I. EXPERIMENTAL NUCLEAR PHYSICS

3-15 Cross Section Measurements with the Fas t Neutron Velocity Selector

Lowell M. Bollinger ,

4 -3 Mass Distr ibution in F i s s ion Louis W. Roeland ,

PAGE

1-15 The Argonne F a s t Neutron Velocity Selector Robert E. Cote ' 1

2-15 Neutron Detectors Roland J. Brown and George E. Thomas 2

5-1 An Area Method for Analyzing Neutron Resonances Lowell M. Boll inger . 11

6-14 Spiral Velocity Selector for Slow Neutrons Roy Ringo 14

8-3 F i ss ion Yield at Different Neutron Absorpt ion Resonances

Sol Raboy. 14

11-15 Instal lat ion and Operat ion of the Van de Gra3.ff Genera tor Jack Wallace. 17

12- (Integrator of Cur ren t in an Ion Beam) F r a n k Lynch *

13-2 Ins t rumentat ion for T ime-of -F l igh t Neutron Spectrometer F r a n k Lynch. 19

14-14 Pulsed Neutron Beams for the Van de Graaff Generator Robert E. Holland 20

* This project is inact ive . Fu r the r r e p o r t s will be made when work is r e sumed .

T^ 15- ( Stopping Cros s Sections of Gases for Heavy Ions)

Merle T. Burgy. . *

16-6 A New Neutron-Counting System F . Paul Mooring.. 21

18-6 Differential Cross Sections for Neutron Resonance Scat ter ing

Raymond O. Lane. 22

20-15 Energy States of Light Nuclei from Charged Pa r t i c l e Reactions

Linwood L. L e e , J r . 23

21-4 Study of Gamma-Rays in Nuclear Reactions Stanley S. Hanna and Luise Meyer-Schutzmeis ter . . . . 23

22-6 Scattering of Charged Pa r t i c l e s Jan Yntema , 27

1 2 3

24-6 The Decay of Sn (125 days) Bradley Burson. 27

25-3 Angular-Dis t r ibut ion Measurements of Cha rged -Pa r t i c l e Reactions

John P . Schiffer 28

26-3 Measurement of Proton Strength Functions John P . Schiffer 29

28-1 Angular Corre la t ions in C h a r g e d - P a r t i c l e Reactions T. H. Bra id 31

32- (Decay of 28 Ni®^ (2.56 hours ) ) Brad ley Burson. *

5 2

33-2 The Decay of 23 Fe (8 hours) Bradley Burson. 32

* This project is inact ive. Fu r the r r epo r t s will be made when work is r e sumed .

152 35-3 The Decay of 9-Hour Eu

Loren C. Schmid 32

52-15 Gamma Rays from Fiss ion Induced by Thermal Neutrons Char les M. Huddleston 32

55-7 Capture Gamma-Ray Spectra for Neutrons with Energ ie s fronn 0.1 to 10 ev.

Car ro l l C . T ra i l 33

56-6 Compton-Elec t ron Magnetic Spect rometer for Neut ron-Capture Gamma Rays

Richard S. P r e s t o n 33

57- (Lifet ime Measurements from Recoil Studies) Stanley S. Hanna *

58 - ( Energy of Delayed Neutrons f rom Fiss ion) Andrew F . Stehney *

60-15 7. 7-Meter Ben t -Crys ta l Spect rometer Be rna rd H a m e r m e s h 34

70-15 Measurements of Nuclear Moments by Angular Cor re la t ion Victor Krohn , 34

80-15 Molecular Beam Studies William Childs 34

81-3 Review Paper on Deposition of Atomic Beams Sol Wexler 35

90-15 Cross Sections for 14-Mev Neutrons H. Casson and L. A. Rayburn 35

91-15 Neutron Transpor t Cross Sections; Angular Distr ibut ion of Scat tered Neutrons

Alexander S. Langsdorf , J r 37

98-14 Total Neutron Cros s Sections in the Kev Region Car l T. Hibdon 38

* This project is inact ive. Fu r the r r e p o r t s will be made when work is r e sumed .

iv

XT 102-9 Neutron Cross Section Measurements by the Self-Indication

Technique C. W. Kimball. 41

106- (Calibration of a Nal Crys ta l and a Long Counter) F . Paul Mooring. *

108-9 An He Neutron Spect rometer F rank J. Lynch 43

110-2 Storage of Pulse-Height Data on Magnetic Tape James B. Baumgardner . 44

117-4 Measurement of Neutron Half-Life Using a Diffusion Cloud Chamber

G. Caglioti and N. D'Angelo 45

121-2 Spin-Momentum Cor re la t ion in the Beta Decay of Po la r ized Li Nuclei

G. R. Ringo. 45

123-2 The Symmetry P r o p e r t i e s of Neutron Decay Sol Raboy 45

125-1 Polar iza t ion of Pos i t rons Demons t ra ted by Annihilation in Magnetized Mater ia ls

R. S. P res ton . 49

138-4 Charac t e r i s t i c s of Multiplier Phototubes Robert K. Swank, 53

139-7 Liquid Scint i l lators Warren L. Buck 53

140- (A Gaseous Scint i l la t ion Counter) Char l e s Eggler . . *

142-9 Elec t ron Acce le ra to r Robert K. Swank 56

* This project is inact ive. F u r t h e r r epo r t s will be made when work is r e sumed .

yn 143-9 Plas t ic Scint i l lators

Louis J. Basi le 59

145-2 Handbook of Nuclear Ins t ruments and Techniques R. K. Swank 60

148- (Elect r ica l Conduction in Dielect r ics) Raymond J. Munick *

149-7 Dynamic Condenser Magnetometer Bradley Burson 61

152- (Radiation Damage to Dielect r ics) Raymond J. Munick *

II. MASS SPECTROSCOPY

17- (Long-Lived Activit ies) David C. Hess *

18-7 Lead Ages of Meteor i tes David C. Hess . 63

19-1 Measurement of Silver f rom the Troi l i te Phase of a Meteori te David C. Hess . 63

20-3 Tr i t ium Age Measurements of Meteori tes David C. Hess 64

27- (Measurement of Top Gas for Borax III) David C. Hess ^ *

28-2 Kinetics of Chemical Reactions in the Gas Phase William A. Chupka. 65

29-9 Gaseous Species in Equi l ib r ium at High T e m p e r a t u r e s Wil l iam A. Chupka 65

* This project is inactive. Fu r the r r e p o r t s will be made when work is r e sumed .

32- (Electron Multipliers in Mass Spect rometry; Effects of Molecular Structure)

Henry E. Stanton *

4 0 4 o 34-13 A - K Dating of Meteori tes

David C. Hess 67

36- (Field Emiss ion Studies) Mark G. Inghram *

38-5 Mass Spec t rometr ic Study of Charged Atomic and Molecular Products of Nuclear Transformat ion

D. C. Hess and S. Wexler 68

40-2 Fragmenta t ion of Methane and Methyl Bromide Henry E. Stanton 72

V. THEORETICAL PHYSICS, GENERAL

2-15 Excited States of Light Nuclei Dieter Kurath. 76

3-5 Dynamics of Nuclear Collective Motion David R. Inglis 76

4- (Investigation of Nuclear Structure) Maria Goeppert Mayer *

5-3 Intermediate Surface Coupling in Even-Even Nuclei B. James Raz. - 78

6- (Polar iza t ion of High-Energy Protons by Scat ter ing) Maria Goeppert Mayer *

7- (Spin-Orbit Coupling in Light Nuclei) Kiuck Lee . .

* This project is inact ive. F u r t h e r r e p o r t s will be made when work is r e sumed .

V l l u. 1 7

9-1 Collective Effects of O B. James Raz 78

12- (Investigation of Neutron Scat ter ing under the Feshbach-Por te r -Weisskopf Model of the Nucleus)

Paul F i s c h e r . *

14- (Analysis of the (d,p) Reactions) B. James Raz. *

15-5 Energy-Leve l Density of a System of F e r m i P a r t i c l e s Norber t Rosenzweig 80

16-1 Analysis of Angular Dis t r ibu t ion Data J. E. Monahan and Gilbert Steiner 81

17-4 Analysis of Angular Distr ibutions and Corre la t ions William C. Davidon 85

18-1 P a r a m e t r i c Formula t ion of Quantum Mechanics William C. Davidon 85

19-4 Ingoing-Wave Condition in Scat ter ing Theory Melvin Hack. 86

20- (Angular Distr ibution of Ine las t ica l ly-Sca t te red Deuterons ) Paul F i s c h e r *

40-4 Quantum Mechanical Ergodic Theorem Hans Eks te in 86

42-4 I r r eve r s ib l e P r o c e s s e s in Quantum Mechanics Hans Ekste in 86

43-2 Fie ld Theory of Nonrelat ivis t ic Moving Nucleons Hans Ekste in and D. Kaplan. 87

44-8 F ixed-Source Meson Theory K. Tanaka. . 87

* This project is inactive. F u r t h e r r e p o r t s will be made when work is r e sumed .

45-8 Meson-Nucleon Interact ion Katsumi Tanaka 87

46 - (Scattering of Pions by Complex Nuclei) Melvin Fe ren t z *

48-3 Dispers ion Relations William C. Davidon 88

50-1 Neutrino Theory M. Goeppert Mayer 89

55- (Spectra of UFg , NpF^ and PuFg ) Maria Goeppert Mayer , *

* This project is inactive. Fu r the r r epo r t s will be made when work is r e sumed .

1-1-15 / 1

I. EXPERIMENTAL NUCLEAR PHYSICS

1-15 The Argonne Fas t Neutron Velocity Selector (5220)

Lowell M. Bol l inger , Robert E. Cote ' and George E. Thomas

Reported by Robert E. Cote '

About two more weeks of work will be r equ i red to finish the

new ro to r . Completion of the work was delayed by changing the sli t s y s t e m ,

essent ia l ly by substi tuting a plast ic mate r ia l for the monel which forms

the cen t ra l s l i t . The other six s l i ts have been finished according to the

or iginal plan.

This change , which involved a change in the shape of the sl i t

as well as a rep lacement of m a t e r i a l , was made to mininnize two undes i r

able effects encountered with the ro tor now in use . The f i r s t of these is an

edge effect which effectively broadens the neutron bu r s t . This is pa r t i cu

l a r ly bad for h igh-energy neutrons and is caused by the fact that the ma te r i a l

which stops the neutrons in tercepts the be a m gradually as the chopper r o

t a t e s . The second effect is the appearance of s t r uc tu r e introduced into the

open beam by the neutron resonances in the ma te r i a l of the ro to r . The f i r s t

effect can be reduced by use of a non- tapered s l i t and the second by making

the sli t of some mate r ia l which has no neutron r e s o n a n c e s , but in which the

mean free path for neutrons is smal l . But s ince non- tapered s l i ts t r a n s

mit neutrons poorly at low e n e r g i e s , it was decided that only one s l i t should

be nnodified. The cen t ra l s l i t of the sys t em was therefore made l a rge r to

accommodate plast ic i n se r t s which form a sl i t 2 1/16 in. high and 0. 015 in.

wide. They a r e made of epoxy r e s i n s t rengthened by l aye r s of glass cloth.

The detector s tat ion at 120 m and the flight tube to this s tat ion

have been completed.

2 O- 1-2-15

2-15 Neutron Detectors (5220)

Lowell M. Bol l inger , Roland J. Brown and George E. Thomas

FISSION DETECTORS Reported by George E. Thomas

A s ingle-pla te fission detector is under construct ion. The foil 2 3 3 2

is 5. 0 x 18. 0 c m and is coated with U to a th ickness of 0. 5 m g / c m . The

foil is mounted on the bottom of the detector with a 1-cm spacing between

both the foil and col lector plate and the col lector plate and top plate of the

detector .

LIQUID SCINTILLATORS Reported by George E. Thomas

The liquid sc int i l la tor desc r ibed in the las t Summary Report

has been completed. The assoc ia ted e lec t ron ics equipment is near ing c o m

pletion and this detector should be t es ted in the very near future. Since it

has s eve ra l p rope r t i e s quite different f rom those of de tec tors used p r e v i o u s

ly, its c h a r a c t e r i s t i c s should prove quite in te res t ing .

ZINC SULFIDE SCINTILLATORS Reported by Roland J. Brown

In an at tempt to improve the detection efficiency of s i l v e r -

activated zinc sulfide in fused boric oxide, f i r s t r epo r t ed in Summary Report

ANL-5667 for September through December , 1956, a laminated s y s t e m of such

sc in t i l la tors was cons t ruc ted . Such an a r r angemen t would be expected to in

c r e a s e the l ight -gather ing efficiency.

The detector was cons t ruc ted of two major components . (1)

A mixture of one pa r t of s i l ve r -ac t iva t ed zinc sulfide to two par t s of boric

oxide was fused, backed with 3-mil a luminum foil and p r e s s e d to a th ickness

of 1.1 mm. F r o m the resu l t ing wafers were cut s t r ips 1 cm by 2 in. (2) Strips

of Lucite of 1-mm thickness were cut to the s ame d imensions .

1-2-15

J' The detector was assembled on the face of a photo multiplier

with both the neutron flux and the planes of the laminae perpendicular to

the photo-surface. Separate scinti l lating units were formed by facing a

s t r ip of the scint i l lator onto each side of a s t r ip of Luci te . Several such

uni t s , separa ted by the aluminum foils , were mounted on the photo multi

p l ier . Efficient optical contact between the layers and with the photo-

multiplier was a s s u r e d by the use of silicone g rease .

The efficiency of this laminated detector was measured as a

function of neutron energy by placing it in the neutron beam of the Argonne

fast chopper with its l ayers para l le l to the paths of the incident neutrons .

The re la t ive efficiency as a function of the energy of the neutrons was

measured by compar ison with the counts produced in a boron-pla te de

tector that was placed between the chopper and the laminated detector .

Counting ra tes as a function of energy were thus s imul tane

ously measured for the two counters . Since the absolute flux as a function

of energy was known from experiments in conjunction with our m e a s u r e

ment of the absolute fission c ross

section of U 2 3 5

the absolute de-

E N E R 6 Y - e v

Fig. 1. Efficiency of the laminated detector .

tection efficiency was determined

by normaliz ing the rat io of the

counting r a t e s . The resul tant ab

solute efficiency of the laminated

detector is shown in Fig. 1.

Next, the relat ive

efficiencies of th ree scinti l lating

sys tems were measured by observing the difference in counting ra t e for

each sys tem when cadmium was inser ted in the beam of neut rons . The

th ree sys tems were : (1) The prev ious ly-descr ibed laminated detector;

(2) Separate s t r ips of the zinc sulfide and boric oxide scint i l lator affixed

direct ly to the face of the photo multiplier in a plane normal to the neutron

b e a m , and (3) Neutron Phosphor NE 400 from Nuclear E n t e r p r i s e s ,

1-2-15 1-3-15

Linaited, s imi l a r ly affixed to the photo mult ipl ier .

These were the observed differences in counting r a t e :

(1) Laminated scint i l la tor 603 / sec / in^

(2) Fla t s t r ips 609 / sec / in2

(3) NE 400 I l 6 l / s e c / i n 2

Thus , we may conclude that the efficiency of the laminated detector

is no g rea te r than that of the flat s t r i p s . Such low efficiencies pe rmi t l i t t le

useful applicat ion, and further study is not planned. Moreover , the NE 400

Neutron Phosphor which was used has only about 4% efficiency at t h e r m a l

energy , far below the adver t i sed 25-35%.

3-15 Cross Section Measurements with the F a s t Neutron Velocity Selector (5220)

Lowell M. Bol l inger , Roland J. Brown, Robert E. Co te ' , Jeanne P . Marion, Adnan Saplakoglu, and George E. Thomas

Reported by Lowell M. Boll inger

2 3 9

a) DETERMINATION OF SPIN STATES FOR PU RESONANCES.

The analys is of the data obtained in a s e r i e s of c r o s s - s e c t i o n m e a s -2 3 9

urements on Pu during the past year has continued. The most signifi

cant r e su l t obtained recent ly is that for t h r e e r e sonances we a r e able to

deduce not only the var ious pa r t i a l widths but also the J -va lues . For the

resonances at 41. 5 and 44. 5 ev , we find that J = 0 whereas for the resonance

at 52. 6 ev , J = 1 with a probabil i ty of perhaps 80%. These a r e the f i r s t

r e sonances for any fissionable nuclide for which the J -va lues have been

determined.

If the ass ignment of the J -va lue for the resonance at 52 ev can be

made nrx>re c e r t a i n , our r e s u l t will be of some impor tance s ince it c o n t r a

dicts the theore t i ca l suggest ion that the r e sonances cor responding to a single

15 5

spin s ta te a r e so broad as to be unobservable. This suggest ion has been put

forth as a possible explanation of the anomolously high fission c r o s s sect ion

in the regions between re sonances .

2 3 5

b) PRECISION MEASUREMENTS OF NEUTRON CROSS SECTIONS FOR U

A new method for measur ing absolute fission c r o s s sect ions in the

t he rma l range of energy was descr ibed in the preceding Summary Repor t ,

ANL-5698. This method, which avoids the known uncer ta in t ies inherent

in other ways of measur ing absolute fission c ro s s sec t ions , was used in a 2 3 5

s e r i e s of measurement s on U The r e su l t obtained is 606 ± 6 barns at

an energy of 0. 0253 ev. This number is not quite a final va lue , but it is

not expected to change by more than 0. 5%.

A compar i son of our r e su l t with those of other measu remen t s 2 3 5

shows that our value is the highest number yet obtained for U In p a r t i

c u l a r , it is much higher than the "world weighted a v e r a g e " value of

579 ± 5 barns and the "world consis tent s e t " value of 582 ± 10 ba rns given

in re fe rence I. This d iscrepancy has caused us to continue our study of 2 3 5

U in the t h e r m a l range of energy by making exceptionally careful m e a s

u remen t s of the total c r o s s sect ion and the re la t ive f ission c r o s s sect ion

as functions of energy.

Our r e su l t for the total c ro s s sect ion is 694 ± 2 b a r n s . This

value is lower than al l values previously quoted, although it is not n e c e s

sa r i ly in d i sagreement with other r e su l t s obtained in the United States . In

any c a s e , our r e su l t is of such high s ta t i s t i ca l quality and is so reproducib le

that we have cons iderable confidence in it. 2 3 5

Our measu remen t s of the re la t ive f ission c r o s s sect ion of U

a r e also of super io r s t a t i s t i ca l quality and many minor s o u r c e s of e r r o r

have been examined with c a r e . Combining these r e su l t s with those f rom the 1 Supplement No. 1 to BNL 325.

L 1-3-15

measu remen t s of the total c r o s s sec t ion , a curve has been derived for

f)/v as a function of energy. Although the final co r rec t ions for this curve

have not been completed , it seems c lear that it is in definite d i sagreement

with the energy dependence found by Palevski in d i rec t measurement s of

Tj (see r e su l t s in re fe rence 1). Our r e su l t s show that39 i nc rea se s slightly

as energy dec r ea se s in the range from 0. 01 to 0, 1 ev.

Of the previous measuremen t s of the absolute f ission c r o s s

sec t ion , that which seems to be most general ly accepted as being free of

l a rge sources of e r r o r has somet imes been t e r m e d the "U. S. " m e a s u r e

ment. In this measurement , the f ission c r o s s sect ion is deduced from the

re la t ionship

* t -""s f I + a

where a = o- /<r, and o- is the r ad ia t ive -cap tu re c r o s s sect ion. The s c a t -

t e r ing c r o s s sect ion <r , which is smal l compared to <r., is es t imated and s t

a is deduced from the measured average value a for a pile spec t rum. This

approach has been r e - e x a m i n e d , using the r e su l t s of our own measu remen t s

of a, and tj^v , A study of the l i t e r a t u r e shows that the most re l i ab le value

of a is 0.180 ± 0. 007; this value was obtained after minor co r rec t ions of

the or iginal data because of changes in other c r o s s sect ion quant i t ies . To

obtain a f rom a , it was a s sumed tha t , in the measurement of a, 4. 6% of

the f issions were caused by neutrons of ep i -cadmium energy and that for

these neutrons the effective value of a is 0. 5. Under these assumpt ions we

find that the f ission c r o s s sect ion is 595 ± 12 barns at 0. 0253 ev. It is no t e

worthy that both this value and the e r r o r a r e much l a r g e r than the resu l t

of 580 ± 7 ba rns which had been obtained previously frona essent ia l ly the same

data. This d i sc repancy only s e r v e s to underl ine the uncer ta in t ies inherent

in the calculat ion. The major difference between our calculat ion and that

for which the r e su l t s a r e given in re fe rence 1 seems to be in the t r e a tmen t of

the effect of epi-Cd neu t rons . The avai lable information seems to indicate that

1-3-15 1-4-3

7

this effect was ignored in previous ana lyses .

The moderate degree of agreement between the r e su l t s of our two

ent i re ly different measurement s of the f ission c r o s s sec t ion , namely

606 ± 6 and 595 ± 12 b a r n s , gives us considerable confidence in the fo rmer

resu l t . It must be emphas ized , however , that these values apply to an

energy of 0. 0253 ev and that they a r e not at all c losely re la ted to effective

pile values or even to effective Maxwellian values . These average values

depend on other c ro s s sect ion quant i t i es , which, as our r e su l t s for 71 Iv

have shown, may not be well understood.

c) MEASUREMENTS of Tj Iv for U

In the preceding Summary Report (ANL-5698) it was r epor t ed that 2 3 5

di rec t measu remen t s of 77/v for U had been completed. These data have

now been examined and those in the t h e r m a l range of energy appear to con

ta in some ser ious sys temat ic e r r o r . The m e a s u r e m e n t s , t he r e fo r e , a r e

now being repea ted ,

4-3 Mass Distr ibution in F i s s ion (5220)

Lowell M. Bol l inger , Louis W. Roeland and George E. Thomas Reported by Louis W. Roeland

As has been outlined in previous r e p o r t s , the p rob lem of this ex

pe r imen t is to detect differences in the mass dis tr ibut ions of the f ission

products produced by groups of neutrons having energ ies cor responding to

different r e sonances in the f ission c r o s s sect ion of the f issionable mate r ia l

being studied. The f i rs t approach to this p rob lem is made in the following

way. F i l t e r s were used in a d i rec t beam from the pile to se lec t energies

which were predominant ly in the des i r ed r e sonances . This neut ron energy

dis t r ibut ion can be checked by making a t r a n s m i s s i o n measu remen t with the

chopper. The fission caused by these neutrons produces two pulses V and V^

^ in a double back- to-back F r i s c h - g r i d chamiber. These pulses a r e fed

into a ra t io c i rcu i t , designed by J. McMahon of the Electronics Division,

which de te rmines the ra t io V^/(Vj^ + V^ ) in the following way. Pulse

No. 1 charges a condenser to the voltage V^ and at the same t ime the sum

pulse s t a r t s a constant cur ren t proport ional to (V^ + V^ ) to d ischarge the

condenser . A negative pulse is produced at the instant the voltage ac ros s

the condenser reaches a maximum

and another when the voltage again

reaches ze ro . (See Fig. 2. ) The

f i rs t of these negative pulses is

used to s t a r t the t ime-of-fl ight

ana lyzer , the second one to stop it.

Under the assumption that the out

put pulse of the counter is p ropor

tional to the energy of the c o r r e s

ponding fragment , it can be shown

that

V. M„

START

(a) VOLTAGE OF CONDENSER

(b) CORRESPONDING PULSES FED INTO TIME ANALYZER

Fig. 2. The conversion of the rat io \ i / ( V i + V2 ) into a t ime proport ional to this rat io , (a) Voltage ac ros s condenser , (b) Corresponding pulses fed into t ime analyzer .

V + V *1 2

M^ + Mg '

where M and M are the masses of the fission f ragments .

A sys temat ic study of the counters was made using the

resul t ing peak- to-val ley ra t io R of the mass yield curve as a c r i t e r ion

of excellence. The resu l t s can be summar ized as follows.

1. The rat io R was the same for p r e s s u r e s of ~ and 1

a tmosphere of 90% A + 10% CH in the chamber .

2. Although no rea l sa turat ion was obtained in the graph

of pulse height vs field between grid and cathode, it was shown that the

peak- to-val ley rat io did not change if one changed the fields within the

region where the saturat ion curve flattens out.

3. The two counters descr ibed in the previous repor t s

gave the same value for R.

1-4-3 9

4. A separa te check of the dependence on the s ize of the

col l imator holes has not been made since the resu l t s thereof seemed obvious

from the r e su l t s for the a - r a y dis tr ibut ion (see the las t Summary Repor t ,

ANL-5698).

5. Runs have been made with different th icknesses of u r a n -_ i - 1

ium foil. A slow l inear var ia t ion of R was obse rved , the value of R 2

being approximately twice as grea t for a foil of 120|jLg/cai th ickness as for

one of ze ro th ickness .

6. The ratio R dec r ea se s with increas ing counting r a t e .

This effect has been accounted for by chance coincidences . After having completed the t e s t s on our counters we s t a r t ed

2 3 5

our p r o g r a m with some orientat ing studies of U . The method we adopted

is the following. By means of a sample changer , a Cd sample is per iodica l ly

taken out of the neutronbeam and rep laced by a non- resonant filter of b r a s s

or carbon of such a th ickness that the counting r a t e s under the two c i r c u m

s tances a r e equal. The two groups of data a r e s to red in the f i rs t and second

halves of the t ime analyzer . In this way we insure identical c i r cums tances

for both r u n s . It is c lear that with the Cd removed the chief contr ibution

to the fission yield is from the t h e r m a l neu t rons , whereas with, the Cd in

the beam the contributing neutrons a r e de te rmined by the fixed f i l t e r s . The

only difference between the two situations could be a different y p i l e -up ,

but this has been proved to have no effect.

The mass -y i e ld curve for t h e r m a l neutrons is used as a r e

fe rence . The AVIDAC computes the ra t io P of the number of counts in a

channel for resonance neutrons to the number in the cor responding channel

for t h e r m a l neu t rons . Several runs have been made us ing , ins tead of neutrons

f rom one r e s o n a n c e , those of al l r e sonances above 1, 5 ev. F igure 3 shows

the dependence of P on the mass number . Apparently the peaks of the d i s t r ibu

tion for the resonance neutrons a r e b roader than those for t he rma l neu t rons .

10 / 0 1-4

100 ISO ZOO CHANNEL NUMBER

£ 5 0

10000

1000

100

IQl 100 ISO 200

CHANNEL NUMBER 250

Fig. 3. Typical example of a mass distr ibution for t h e r mal neutrons and of the ra t io P for all neutrons with energy >1. 5 ev for U^^^.

We have repeated this measurement

under slightly different c i r c u m

stances and the resu l t was always

qualitatively the s a m e . As can be

seen from the chopper data for the

fi l ters used in this exper iment ,

this effect cannot be caused by fast

neutrons . The difference between

the two distr ibutions is shown most

re l iably on the wings of the peaks

where the s ta t i s t ics a re good. There

the effect cannot be explained in

t e rms of a background effect since

the background requ i red would have

to be grea te r than the observed

counting ra t e in the valley of the

distr ibution.

The next s tep was to i s o

late the 8. 9-ev resonance of U ^ ^ .

We succeeded in producing a beam which gave 50% of the fissions due to

this resonance and 50% due to background. The influence of this back

ground can be measured by removing the 8. 9-ev resonance with Sm and

measuring P again.

The resu l t s of this study a r e inconclusive because of 2 3 3

poor s ta t i s t i cs . We shifted attention to the eas ie r study of U

This experiment is eas ie r because the resonances under

study (1. 8 and 2. 3 ev) have such a huge contribution to the fission as com

pared to the o the rs . Bes ides , the MTR group has shown from c ros s

section behavior that these resonances in terfere with each other but not

with the resonance at negative energy, which is mainly responsib le for the

the rma l c ro s s section. Therefore it is expected that the 1. 8- and 2. 3-ev

-5-1 11

resonances a r e assoc ia ted with one spin s ta te of the compound nucleus w h e r e

as the resonance at negative energy is assoc ia ted with another spin s t a te .

This difference should also show up in the mass-yield dis t r ibut ion, pa r t i cu

l a r ly in the peak- to-va l ley ra t io . The uran ium foil used in this exper iment

is only 2 |j.g/cm thick to prevent excess ive a p i le -up .

F i r s t of all we have compared the total contr ibution of

the two resonances with the contribution of t h e r m a l neut rons . The r e su l t s

s e e m to indicate c lear ly that the peak- to-va l ley ra t ios a re different, the

I, 8- and 2, 3-ev resonances having a lower valley and probably also n a r r o w e r

peaks . However , we cannot be ce r t a in that this effect is r e a l until it has been

obtained under different exper imenta l conditions.

The compar i son of the r e su l t s for the resonance at I, 8 ev

with those at 2. 3 ev was inconclusive because of s t a t i s t i c s .

The above studies a r e being continued under improved

ins t rumenta l condit ions.

5-1 An Area Method for Analyzing Neut ren Resonances (5220) ' — • " • • • * • • " ' • " • • " . " • — I I . I - . . M I II - l . l , . — l — I — ^ — » • I . -

Lowell M. Bollinger and Jeanne P. Marion Reported by Lowell M. Bollinger

In spite of rapid improvement in the techniques of m e a s

uring c r o s s sect ions for neutrons of IOAV energy , the ins t rumenta l reso lu t ion

used is r a r e l y good enough to o b s e r v e , without se r ious d is tor t ion , the sha rp

resonances which a r e cha rac t e r i s t i c of this range of energy. F o r t r a n s m i s s i o n

m e a s u r e m e n t s , t h e r e f o r e , the total a r e a above the observed t r a n s m i s s i o n dip

is widely used to de te rmine some functional re la t ionship between the peak c r o s s

sect ion o- and the total width of the r e sonance . The many spec ia l ized t e c h

niques employed to t r e a t data in this way have been s u m m a r i z e d by Melkonian.

1 E. Melkonian, Proceedings of the Internat ional Conference on the Peaceful

Uses of Atomic Ene rgy , Geneva, 1955 (United Nat ions , New York, 1956) Vol. 4 , p . 340.

12 ) y _ 1-5.1

The basic idea of all of them is that the nature of the re la t ionship between

o-Q and r depends on the sample th ickness n. Thus the independent values

of ITQ and P a r e those values which a r e allowed by the a r e a s obtained for

s e v e r a l different th icknesses of sample .

The pr incipal weakness of the method of a r e a analysis

that has been used here tofore is i ts lack of sensi t ivi ty. Because the s e v e r a l

l ines of g- vs F c r o s s at an acute angle , sma l l e r r o r s in the measured

a r e a s r e su l t in l a rge e r ro r s in the derived p a r a m e t e r s . We have developed

a new a r e a method for t rea t ing t r a n s m i s s i o n data which can significantly

improve the accuracy of the p a r a m e t e r s without increas ing the calculat ional

labor involved. The bas ic idea of the new naethod is that the pa r t i a l a r e a

above some l imi ted range of energy of a t r a n s m i s s i o n dip is vised d i rec t ly

in the calcula t ion, in con t ra s t to the previous method in which the ent i re

a r e a is t r ea ted .

To make this new approach poss ib le , the pa r t i a l a r e a s I

A above the t r a n s m i s s i o n curve within the range of energy from (E - £) hj o

to (E + e ) have been calculated* for a wide range of conditions f rom the

re la t ionships

A ^ = / - ( l - e - " ^ ) d E

- ( x - y ) ^ / 4t and . = . ^ y ^ ( x , t ) = ^ ^ - ^ ^ p dy

where x = — (E - E Q) and t = (-j

In the above, o- is the c r o s s sec t ion , E is the neutron energy , E is the r e

sonance energy , and A is the Doppler width of the r e sonance .

Values of A were calculated for no- ranging from 0,1 E o

to 150, for A / r from 0, 2 to 10, and for values of € / A of 0. 5 , 0, 75 , I, 0,

I, 5, 2. 5, 3. 5 , 5. 0 and 7. 5. These r e su l t s have been plotted in the fo rm of

* The calculat ion was done by A. J. Strecok of the Applied Mathematics Division.

A / A vs no-Q for a s e r i e s of values of A/r* and a fixed value of e / A .

One of them is i l lus t ra ted in Fig. 4. For use in t rea t ing data , all of the

curves have been drawn to a la rge scale on gridded pape r , where the

quantities involved can be read easi ly to an accuracy of 0. 5%. The author

Fig. 4. A simplified representa t ion of one of the families of calculated curves relat ing the par t ia l a reas A ' above t r ansmis s ion dips to the resonance p a r a m e t e r s .

would be pleased to supply this set of curves upon request .

Our application of the new method to actual t r ansmis s ion

data has shown that it has the following advantages as compared to the

older approach in which the whole t r ansmis s ion a rea is used.

a) The accuracy of derived p a r a m e t e r s is improved.

E r r o r s in p a r a m e t e r s a r e usually reduced by a factor of about 1. 5 although

in special cases (as when the resolut ion width is na r rower than the r e

sonance width or when the thicknesses of the available samples a r e all

nearly equal) the degree of improvement can be much more spectacular .

b) Resonance p a r a m e t e r s can be derived from the r e

sults of measurements on a single sample . This is done by obtaining

curves of (r_ vs P for two values of e /A and is to some extent a

14 1-5-1 jn 1-6-14

r 1-8-3

subst i tute for curve fitting.

c) The effect of an a s y m m e t r y in the shape of a resonance

is miinimized since the re la t ive magnitude of an in ter ference t e r m is sma l l e s t

in the immedia te neighborhood of the resonance . Moreover , e r r o r s caused

by the overlapping of a nearby resonance a r e reduced. These considera t ions

a r e especial ly important for the fissionable m a t e r i a l s , for which the level

spacing is smal l and a s y m m e t r i e s in shape a r e common.

6-14 Spiral Velocity Selector for Slow Neutrons (5220)

Rauf Nasuhoglu and Roy Ringo Reported by Roy Ringo

A new shield has been designed for this velocity s e l e c

tor and is now under construct ion. It is intended to give adequate radia t ion

shielding and great ly inc reased protect ion against the hazard of a burs t ing

ro to r .

8-3 F i s s ion Yield at Different Neutron Absorption Resonances (5220)

Lawrence Glendenin (Chem. D i v , ) , Rauf Nasuhoglu, Sol Raboy, Roy Ringo, and El l i s Steinberg (Chem. Div, )

Investigations of the var ia t ion of f ission yield with

mass have been made under a wide va r ie ty of exper imenta l condi t ions , but

these studies have not included f ission induced by resonance neutrons of

well-defined energy. A determinat ion of the re la t ive probabi l i t ies of s y m

met r ic and a s y m m e t r i c modes of f ission at specific r e sonances miight give

further insight into the na ture of the fission p roces s and the p rope r t i e s of

the s ta tes of the compound nucleus cor responding to the r e s o n a n c e s . In par t ic

u l a r , Bohr has p resen ted qualitative considera t ions re la t ing the re la t ive

1

A. Bohr , "Proceedings of the Intl, Conf, on the Peaceful Uses of Atomic E n e r g y " , (United Nat ions , New York, 1955), Vol, 2 , p, 151,

1-8-3 15

probabil i t ies of symmet r i c and a symmet r i c fission modes to the spin and

pari ty of the state of the compound nucleus.

Measurements of v , the number of neutrons per f ission,

have indicated that this quantity remains essent ia l ly constant for all r e -

sonances. However it was felt that study of the features of the curve of

yield vs mass would provide a more

sensi t ive measure of possible differ

ences in fission modes at different

resonances . 2 3 5

Samples of U

metal (about 90 gm,each 1 cm x 1 cm

X 10 cm) were i r rad ia ted with neu

t rons from a c rys ta l spec t romete r

in the a r rangement shown in Fig. 5.

Neutrons of 1.1, 3. 1, and 9. 0 ev were

used in a s e r i e s of i r r ad i a t i ons , each

last ing for about th ree days. The

beam used in these i r radia t ions was

about 11 cm high at the position of

the sample and contained about 10

neutrons per second in the energy

region of in teres t . The resolut ion of

the instrument (full width at half maxi

mum) was about 5. 3% at 1 ev and 15%

Fig. 5. Horizontal c r o s s s e c tion of the c rys ta l spec t ro meter for neutrons at the Argonne Research Reac to r , C P - 5 . The beam is mono-chromat ized by reflection from the ver t ica l 110 planes of a Be c rys t a l approximatel y ! . 5 c m x l . 5 c m x 7 c m high.

at 9 ev. Background i r radia t ions were

performed by turning the c rys ta l about 2 from the direct ion satisfying

the Bragg condition for reflection.

Auclai r , Landon and Jacob, Compt. rend. 241, 1935 (1955); Z i m m e r m a n , Palevsky and Hughes, Bull. Am. Phys. Soc. 1, 8 (1956); Leonard , Seppi and F r i e s e n , Bull. Am. Phys. Soc. l^, 8 (1956); Bol l inger , Co te ' , Hubert , LeBlanc and Thomas , Bull. Am. Phys. Soc. 1, 165 (1956).

Standard radiochemical procedures were carr ied out on 8 9 1 1 1 1 1 5 1 2 7

the irradiated samples for Sr , Ag , Cd , and Sb . Comparisons

of the counting rates observed were made with samples of the same nuclides

isolated from samples of normal uranium irradiated by slow (pile) neutrons,

and mounted and counted in an identical manner. Calculations of the fission

yields could thus be made on a relative basis , using the known yields for 2 35

fission of U by slow neutrons, and avoiding corrections for geometry, scattering, absorption, etc. Initial counting rates of the order of 5 c /m

1 1 5

were observed for Cd This was sufficient to characterize the radiations

by decay measurements. All samples were counted in an anti-coincidence

shielded counter having a background of about 2 c/m. The results are

summarized in Table I, 2 35

TABLE I. Fission yields in fission of U by resonance neutrons from 1-10 ev.

Nucl ide

8 9 Sr

1 1 1 Ag

1 1 5 Cd

1 2 7 Sb

1.1 ev

4 .8%*

0.020%

0 .013%

0, 11%

3 ,1 ev

4 ,8%*

0.019%

0,008%

9. 5 ev

4 ,8%*

0,018%

0.010%

Pi l e

4 .8%*

0.018%

0.011%

0.10%

a Assumed yield; others calculated relative to Sr®®.

The preliminary data indicate no differences in the re la -89

tive probabilities of asymmetric modes (represented by Sr ) and near-1 1 1 1 1 5 1 2 7

symmetric modes (represented by Ag , Cd , and Sb ). The accuracy

of the measurements of fission yield is estimated as ± 20%. The extremely 1 1 5

low counting rates for Cd and the rather high background effect (varying

from about 20% to 1,1 ev to about 50% at 9. 5 ev) would preclude any observa

tion of a real decrease in the probability of symmetric fission modes. However,

1-8-3 1-11-15 17

the data can cer ta in ly be taken to show that no significant i nc r ea se in

these modes occurs at the resonances investigated. Fu r the r studies a r e

planned with inc reased sensi t ivi ty and reduced background so that regions

between resonances may be investigated a lso .

This r epor t will be submit ted for publication.

11-15 Installation and Operat ion of the Van de Graaff Generator (5220)

Robert Holland and Jack Wallace Reported by Jack Wallace

The repor t covers the operat ion of the Van de Graaff

Generator in D-203 for the period Apri l 1 through June 30, 1957.

The generator was used to acce l e ra t e p ro tons , deuterons 3

and alpha pa r t i c l e s . The generator was also opera ted with He (over 90%)

as the gas in the ion source .

The following t ime distr ibution shows both the division

of t ime and the types of exper iments being per formed with the Van de Graaff

Generator by the group. No effort has been made to show any efficiency

factor for the use of the allotted t ime by the var ious e x p e r i m e n t e r s ,

1. Photo-f iss ion Cros s Sections of the Heavy Elements

2. Angular Distr ibutions of Neutrons

3. Angular Distr ibut ion of Protons

4. Angular Distr ibut ion of -y-rays

5. Neutron Spectra by Time of Flight

6. I r rad ia t ion of Targe t s

7. Total Cross -Sec t ions

8. Pa r i ty Exper iment

663,0

Clark

Lane , Langsdorf

L e e , Schiffer

Hanna, Meyer

Holland

Mooring

Hibdon

Hanna, P r e s t o n

111.7 hours

216. 0

112. 5

40. 2

76 .3

8. 3

35 .9

62, 1

18 n 1-11-15

Star t -up and daily maintenance 45, 0

Machine r e p a i r s and changes 377, 0

Exper imenta l setup t ime 83, 0

Total t ime available (64 days x 15 hours + 26 days x 8 hours) l l 6 8 , 0

During this quar ter tlie life of the charging bel ts became

so shor t that even though the demand for machine t ime was ve ry grea t we

were forced to take action to t r y to remiedy the si tuation. There were

two possible sources of t rouble that could cause shor t belt life. One cause

would be cons idered mechanical in na ture and the other e l ec t r i ca l . Not

being able to de te rmine which was the r e a l culpr i t or whether both were con

t r ibu t ing , we decided to a t tack both p rob l ems .

The p rob lem which I choose to cal l mechanical deals with

such possibi l i t ies as an imiproper sys t em of maintaining the tension of

the be l t , improper crowning of belt pu l l eys , imperfect ions in the manu

facturing of the be l t , and improper width, weight or coating of the belt .

Each of these poss ib i l i t ies was invest igated and co r rec t ions were made ,

or a r e being made , to insu re al leviat ion of any cause of e r r o r . The p r o b

l e m was also d i scussed with the belt manvifacturer to see if he might have

an answer to the p rob lem. There appeared to be no glar ing defects to

which the t rouble could definitely be a t t r ibuted.

The a t tack on the e l ec t r i ca l p rob lem was a lso a posit ive

action. For some t ime we have been aware that our bel t -charging sy s t em

left much to be des i red . We knew that we were getting incomplete charge

r emova l at the high-voltage end of the genera tor and that the belt was c a r r y

ing a surplus posi t ive cha rge . Another disadvantage was that our charging

s y s t e m at the high-voltage end of the ma.chine also affected the focus of the

beam. The th i rd objection was that the sy s t em was so complex that it was

ha rd to analyze what was going on. Hence the charging s y s t e m at the high-

voltage end has been rep laced with a var iab le power supply that sp rays a

11-15 1-13-2 19

negative charge on the r e t u r n run of the belt . The charging sys tem at the

ground end remains the same as before. This allows the charge on the

belt to be control led at both ends of the machine, which makes possible a

balanced charge on the belt . It has el iminated the objectionable p rob lems

in the old charging s y s t e m , but as yet we a r e not su re no new prob lems were

introduced and we also a r e not su re how much, if any, the excess posit ive

c h a r g e , unbalanced c h a r g e , etc . affected the life of our charging be l t s . At

the t ime of this wri t ing, it is too ea r ly to say how much we have been able

to i nc r ea se the belt life with the above changes .

Other sources of t rouble during this per iod were routine in

na tu re . The l a rges t loss of t ime was in working out changes and problems

brought about by the above changes in the sy s t em of belt charging.

The generat ing vol tmeter w^hich measu re s the charge on

both runs of the belt has been made more re l iab le and is in constant use

with the new bel t-charging sys t em.

13-2 Ins t rumentat ion for T ime-of -F l igh t Neutron Spec t romete r (5220)

Robert Holland and F r a n k Lynch Reported by F rank Lynch

A. MEASUREMENT OF THE SPREAD OF ELECTRON TRANSIT "TIMES IN PHOTOMULTIPLIERS

To produce light pulses of u l t rafas t r i s e t i m e , a light

sou rce s imi la r to that developed by Quentin Kerns at U. C. R. L. at Berke ley

has been const ructed. It cons is t s of a 125-ohm coaxial line in which is

placed a r e l ay with mercury -we t t ed con tac t s , and a s imp le te lescope focused

on the r e l ay contacts . Light f rom the a r c produced in the hydrogen-fi l led

r e l ay when the contacts c lose is focused upon a spot on the cathode of a photo-

mult ip l ier . The e l ec t r i ca l pulse f rom the r e l ay t r i g g e r s the sweep of a

t ravel ing-wave osc i l loscope , and the pulses f rom the las t dynode and plate

of the photo multiplier 8 a r e applied to the two deflection he l ices . The r i s e

t ime of the pulse from the photo multiplier is ca l ibra ted by varying the

length of coaxial line in the t r igger c i rcu i t . By focussing the light flashes

on different a r e a s of the photo-cathode, differences in t r a n s i t t imes f rom

the different places of or igin of the photo-e lec t rons may be invest igated.

B. TIME-INTERVAL VERNIER

The pulses into the 125-ohm circula t ing l ine should be of

minimum durat ion (less than 5 mjj.sec) and of maximum ampli tude. M e a s

u remen t s a r e being ftiade with the E F P - 6 0 tube to de te rmine the operat ing

voltages that will pe rmi t g rea tes t output cu r r en t and fas tes t r i s e t ime .

1 •

Type 2236 manufactured by Edger ton , Germeshausen and G r i e r , Inc, , Boston, Massachuse t t s .

14-14 Pulsed Neutron Beams for the Van de Graaff Genera tor (5220)

Robert E. Holland

The data on the angular dis t r ibut ion of the neutrons f rom 5 5 5 5

the reac t ion Mn (p ,n)Fe were re taken because those mentioned in the p r e

ceding repor t showed l a rge fluctuations caxised by the lack of a good monitor .

Although both runs gave essent ia l ly the same r e s u l t , only the more recen t

data a r e p resen ted h e r e .

Targe ts were p r e p a r e d by evaporat ing manganese on

a luminum backings which were weighed before and after evaporat ion to obtain

the t a rge t th ickness . Background was obtained at each angle by r e v e r s i n g

the t a rge t so as to p r e sen t ba re a luminum to the beam. A long counter kept

in a fixed posit ion below the plane of measuremen t s e rved as a monitor.

1-14-14 1-16-6

21

Figures 6 and 7

show the angular distr ibutions of the

neutron groups corresponding to 5 5

t rans i t ions to s ta tes of Fe obtained 5 5 5 5

from the react ion Mn (p,n)Fe

with a mean proton energy of

3. 060 Mev and a ta rge t thickness

of 38 kev. The data have been c o r

rec ted for var iat ion in the monitor

count (less than 3%) and for

variat ion in counter efficiency

(less than 2% for the three lower

s ta tes) . The cor rec t ion for t r a n s

forming to cen te r -o f -mass coordi

nates is smal l (the maximum co r

rect ion in angle is 1. 3° and that in

solid angle is less than 1%) and was

not made. All neutron groups ex-

GROUND STATE 420 Kiv STATE

- 3 0 0 30 60 90 120 ISO ISO -30 0 30 60 90 120 ISO 160 ANGLE B ANGLE 9

Fig. 6. Angular distr ibution of neutrons from Mn (p,n)Fe

930 Kiv STATE

r^^, - -1-

- 3 0 0 3D 60 90 tZO ISO ISO ANGLE S

-30 0 30 60 90 120 ISO 160 ANGLE S

Fig. 7. Angular distr ibution of neutrons from Mn (p,n)Fe .

cept the ground-state group were isotropic within the accuracy of m e a s

urement . The angular distr ibution of the ground-s ta te group is well

r epresen ted by

1 2 I ( e ) = 1 + 2 cos e ,

which is the curve in Fig. 6, There were not enough data at back angles

to rule out a smal l cos 0 t e r m .

16-6 A New Neutron-Counting System

Clyde Kimball and F . Paul Mooring Reported by F . Paul Mooring

(5220)

P a r t s for the two identical neutron counting assembl ies

a re now being delivered from the shops. Electronic c i rcui t s a r e being

built and should be finished soon.

22 1-16-6 9 1 1-18-6

During the next q u a r t e r , t e s t s will be made to se lect the

actual locations of the th i r ty or more BF^ counters that will be used in

each assembly . It is planned to instal l the two new counter sys t ems at

the Van de Graaff genera tor during the s u m m e r . The grate floor of the

Van de Graaff r oom has been extended to provide r o o m for the new

a s s e m b l i e s .

18-6 Differential Cross Sections for Neutron Resonance Scat ter ing (5220)

Raymond O. Lane

6 Angular dis t r ibut ions of neutrons s ca t t e r ed f rom Li and

7

Li have been measured at eight angles with the l a rge detector tanks on

the c i r cu la r t r ack . Data were taken from 0.100 Mev to 0. 600 Mev with

n a r r o w resolu t ion (/v 5 kev) , and from 0. 600 Mev to 2. 200 Mev with very

broad resolut ions {rJlOO kev). Use of the a l t e rna t ing-grad ien t magnet ic-

focusing lens provided a proton beam of 20-25(ia on the rotat ing Li t a rge t

which allowed data to be obtained with high resolu t ion and good s t a t i s t i c s

for these samples for which the c r o s s sect ion is very low. The AVIDAC

analys is of the angular-distr ibvit ion data is being r ev i sed to take advantage

of the added angles made available s ince the detector tanks have been on a 6 7

c i r cu l a r t r ack . It is hoped that the data on Li and Li can be analyzed

soon. Similar m.eaflurements with high resolu t ion have been made on 32

S near the 0. 585-Mev resonance in an a t tempt to de te rmine the value of

the higher o rde r t e r m s in the differential sca t te r ing c r o s s sect ion. E a r l i e r

exper iments showed that J 1^5/2, I'^ 2 for this r e sonance . These da ta ,

t oo , a r e awaiting analys is with the new p r o g r a m .

Through the col laborat ion of W. Miller and W, Snow of the

Applied Mathematics Division, the Monte Car lo calculat ion of the multiple

sca t te r ing of neut rons near r e sonances has been completed. It t ake s into

18-6 1-20-15 ^^

1-21-4

account d i rect ly the f i rs t t h ree o r d e r s of sca t te r ing for the s lab- type geo

metry used he re . Because of shut-downs of the AVIDAC, only one t e s t case

has been completed so far; but al l the resonance sca t te r ing data obtained so

far will be co r r ec t ed as soon as t ime on the machine is avai lable .

The differential sca t te r ing c r o s s sect ion for carbon in the

vicinity of the 2, 07-Mev resonance will be measured soon with high r e so lu

tion to de te rmine the value of the h igh-order t e r m s in the c r o s s sect ion and

the sca t te r ing phase shifts in this region.

The semi-au tomat ic equipment for record ing the a n g u l a r - d i s

tr ibution data on punched tape is undergoing its final tes t ing pr ior to its

contemplated use on the next s e r i e s of m e a s u r e m e n t s . This will provide

data tapes ready to be fed direct ly into AVIDAC or GEORGE for ana lys is .

20-15 Energy States of Light Nuclei f rom Charged Pa r t i c l e Reactions (5220)

Stanley S. Hanna, David R. Ingl i s , Linwood L. L e e , J r . , and John P . Schiffer Reported by Linwood L. L e e , J r .

The new t r ack for the m^agnetic spec t rome te r has been c o m

pleted and is r eady for instal lat ion. Work is continuing on the new ta rge t

chamber and other equipment for the new instal lat ion.

21-4 Study of Gammia-Rays in Nuclear Reactions (5220)

Stanley S. Hanna and Luise Meyer-Schi i tzmeis ter

6 l O

The angular distr ibut ions obtained in the Li (a, Y)B r e

action have now been compared with theore t ica l dis tr ibut ions for a var ie ty

of a s s ignments . The resonances and gamma rays which have been observed

a r e repor ted in Table II. The measured angula r -d i s t r ibu t ion coefficients

a r e given in Table III. The compar i son with the theore t i ca l coefficients is

24 1-21-4

presen ted in tabular form in Table IV. 6 IQ

TABLE II. Resonances and Gamma Rays Observed in Li (a,'Y)B The c ro s s sect ion is expres sed in the form w ='ircr_,r/X .

E a

(Mev)

0 .50*

1.085

1. 175

2.435

2.605

E ex (Mev)

4 ,77*

5, 105

5. 16

5.91

6,02

r (lab) (kev)

.- 7

3

20

5

P r i m a r y E

(Mev)

4, 77

4 ,05

5. 105

4 ,39

5,16

4 ,44

3.01

5.91

6.02

Radiation % w(CM)

(ev)

8

92

96

4

7

29

64

100

100

0. 10

0.005

0.04

0, 15 r

0,32 S

( 0.

Secondary Radiation

(Mev)

0, 72

0.72

0 . 72

2 , 15

1,43, 0, 72

4 1 , 1 , 0 2 , 0 , 72

These values a r e taken from the l i t e r a tu re .

TABLE III. Observed angular dis t r ibut ion coefficients in the express ion 2 4 6 lO

w( 0) = 1 + A2 COS 0 + A4 COS Q for the reac t ion Li (a,-Y)B . A value of A4 is given only in cases in which it s e e m s s ta t i s t ica l ly significant. Values co r r ec t ed for the finite solid angle a r e l i s ted in the final columns. The e r r o r in each coefficient is approximate ly ± 0 .1 .

B l e v e l E Measured Cor rec ted (Mev) (M^v) A2 A4 Ag A^

- 1 . 4 4 . 4 - 3 . 4

- 0 . 0 6

- 0. 35

0.06

- 0.25

- 0.25

4. 77

5. 11

5. 16

4. 05

0, 72

5. 11

5,16

4 .44

3. 01

2 .22

- 0 , 05

- 0 , 3 0

0. 05

- 0.20

- 0,20

1-21-4 25

l o B l e v e l (Mev)

5 .91

6 . 0 2

(Mev)

5 . 9 1

6 . 0 2

Me

^

0 .00

- 0. 10

a s u r e d

^ 4

1. 05

C o r r e c t e d

A . A ,

0 . 0 0

- 0 . 8 0 2. 0

T A B L E IV. C o m p a r i s o n of e x p e r i m e n t a l and t h e o r e t i c a l a n g u l a r d i s t r i b u t i o n s . If t h e e x p e r i m e n t a l v a l u e s of A2 and A4 (Tab le III) c a n be o b t a i n e d t h e o r e t i c a l l y for a g iven a s s i g n m e n t , t he c o n d i t i o n for t h i s a g r e e m e n t is l i s t e d (un l e s s the t h e o r e t i c a l v a l u e s a r e unique) and the a s s i g n m e n t i s l a b e l e d P ( p a s s i b l e ) . If, on t h e o t h e r h a n d , the t h e o r e t i c a l v a l u e s of A2 and A4 , a s l i s t e d , a r e i n c o m p a t i b l e wi th e x p e r i m e n t the a s s i g n m e n t i s m a r k e d N (Nt>t p o s s i b l e ) . B o r d e r l i n e s i t u a t i o n s a r e l a b e l e d U (Uncer ta in ) , The a l p h a - p a r t i c l e and g a m m a - r a y i n t e n s i t i e s wi th a n g u l a r m o m e n t u m equa l to i a r e d e n o t e d by I ( i ) and I (i ) , r e s p e c t i v e l y ,

a y

. 10 , B l e v e l A s s i g n -(Mev) ment

•y-Ray (Mev) Th i s a s s i g n m e n t r e q u i r e s C o n c l u s i o n

4, 77 0

l ^ 2 •

A4 = Ag = 0

A^ = 0

I ( 2 ) / I (1) = 1.8 Y Y

A4 ^ Ag « 0

A4 = - 0 . 5 6 , Ag = 1.33

I ( 4 ) / I (2) = 0 , 9 2 a a

N

N

P

P

N

P

0. 7 A TH Ag « 0

5, 11

5, 16

0"

1±

2 "

2+

3 "

3 +

4 "

0"

1"

Al l

5, 1

5. 1

5. 1

5. 1

5 . 1

5, 1

Al l

| 5 . Z

( . 4 , 4 , 3 . 0

A4 = Ag = 0

Ag > - 0 . 1 0

Ag > - 0 . 18

I ( 2 ) / l (1) = 0, 06 o r 00 Y Y

A^ = 0 , Ag = 0 . 7 0

I ( 4 ) / I ( 2 ) ~ 1 a a

A g . ^ - 0 , 3 9

A^ = Ag = 0

A^ = 0 , Ag = - 0 , 10

A^ = 0 , Ag = - 0 . 33

N

N

N

P

N

U

P

N

U

1 0 B l e v e l (Mev)

A s s i g n ment

•y'-Ray (Mev)

^

T h i s a s s i g n m e n t r e q u i r e s

1-21-4

C o n c l u s i o n

5 . 2 , 4 , 4 , 3 . 0

U . 4 , 3 . 0

U . 4 , 3 . 0

( . 4 . 4 , 3 , 0

U . 4 , 3 . 0

I ( 2 ) / I (0)^5/1.5 a a

A^ = 0 , A g < - 0 , 0 5

I ( 3 ) / I (1)> 0 .50 a a

I (2 ) / I (1) = 0. 02 o r 9 Y Y

I (2 ) / I (1) = 0. 01 o r 150 Y Y

A^ = 0 , Ag = 0 , 7 0

A^ = - 0 . 5 4 , Ag = 1. 33

I ( 2 ) / I (1) = 0,16 Y Y

A^ + A g > 0 . 7 5

P

U

P

P

P

N

N

P

N

5 . 9 1 0-

1"

1-

2"

z' 3'

3^

4 '

5.9

5.9

5.9

5.9

5.9

5.9

5.9

5.9

5.9

A^ = Ag = 0

0.10 A4 = 0 , Ag

0 < : i ( 2 ) / I ( 0 ) ^ 1

I ( 3 ) / I ( 1 ) > 0 . 1 5 a a

I ( 2 ) / l (1 )«10 o r 0 . 0 1 Y Y

A^ = 0 , Ag = 0.70

I ( 2 ) / I ( l ) a J 0 . l 6 Y Y

A g ^ - 0 . 3 9

I (2 ) / I ( l ) a 0 . 0 4 Y Y

P

P

P

P

P

N

P

N

P

6.02 0 +

l - , 2

2"

3

4 '

6.0

6.0

6,0

6.0

6,0

6.0

6.0

A^ = Ag = 0

A , = 0

A^ + A g < 0 . 5 0

A4 = 0 , Ag = 0 . 7 0

A^ < : o . 8 0

A , = 0

I ( 2 ) / I (1) = 9 . 0 Y Y

N

N

N

N

N

N

P

1-22-6 1-24-6 27

22-6 Scattering of Charged Pa r t i c l e s (5220)

Jan Yntema

The construct ion and instal lat ion of the sca t te r ing chamber is

now complete . The remote control equipment and TV c a m e r a s a r e now

operat ing.

24-6 The Decay of Sn (125 days) (5220)

Bradley Bur son and Lor en C. Schmid Reported by Bradley Burson

New samples of enriched isotopes of tin have been obtained f rom

Oak Ridge National Labora to ry . After i r rad ia t ion in C P - 5 for 17 days , a 1 2 2

sample of enr iched Sn was allowed to "cool" for 14 days and then subjected

to chemiical purification to remove t r a c e s of antimony.

The gamma rays r epor t ed e a r l i e r a r e a lso seen in this source 1 2 3

of Sn . In the ea r l i e r s a m p l e , the intensity of the peak at 1. 08 Mev was 1 1 3

approximately 0. 8% of that of the 0. 395-Mev peak from Sn . In the p resen t

sample the intensity of the 1. 08-Mev peak is about 15% of that of the 0. 395-Mev

radiat ion. This enhancement is a t t r ibuted to the g rea te r degree of en r i chment ,

of the new iso topes .

F r o m the new g a m m a - r a y s p e c t r u m , it is definitely evident that

the radia t ion in the region of 0. 60 Mev is complex. The intensi ty is s t i l l

ve ry low, but the re appear to be two peaks r ep resen t ing gamma rays of

0. 60 and 0. 68 Mev respec t ive ly . These have intensi t ies of 1. 3% and 0. 83%

re la t ive to the 0. 395-Mev gamma ray . Because of the unrel iabi l i ty of the

e a r l i e r data in this reg ion , no effort to compare intensi t ies is being made.

Seven of the t in isotopes were i r r ad ia t ed . The only source in which 1 2 2

the 1. 08-Mev peak appeared s t rongly was the act ivated Sn . This radia t ion

pe r s i s t ed after chemica l purification. It is therefore evident that at leas t one

28 1-24-6

1 2 3

gamma r ay is p resen t in the decay of Sn . As has been mentioned, none

have been repor ted to date .

We have definitely establ ished that the 0, 255-Mev gamma 1 1 3

r a y d iscussed ea r l i e r in this study is assoc ia ted with the decay of Sn

These investigations will be d iscussed subsequently under a different head-1 1 3

ing —The Decay of Sn (112 days).

25-3 Angular-Dis t r ibut ion Measurements of Cha rged -Pa r t i c l e Reactions (5220)

Linwood L, L e e , J r . , and John P . Schiffer Reported by John P, Schiffer

1 1 1 4 The B (a,p)C reac t ion has been studied with a lpha-

1 1 par t i c le energies between 2 and 4 Mev. A ta rge t of highly enr iched B

was purchased for this purpose from the Atomic Energy R e s e a r c h E s t a b -1 1 1 4

l i shment at Harwell , Several of the r e sonances observed in the B (a,n)N 1

reac t ion were seen. The prominent resonance seen in the (a,n) reac t ion

at 2, 06 Mev was r epor t ed as ent i re ly absent in the (a,p) yield in the work 2

of Shire and Edge. Our exper iment is in d i sagreement with these m e a s

u rements in that we very c lea r ly observe this resonance with a c r o s s sect ion

that seems considerably l a rge r than the l imi ts set in the ea r l i e r work. The

single resonance r epor t ed in the (a,n) work at 2, 60 Mev was observed as

a doublet in the p resen t work.

About twenty angular d i s t r ibu t ions , covering seve ra l of

the observed r e s o n a n c e s , have been measured . An analysis in t e r m s of

Legendre polynomials is planned in o rde r to ass ign J -va lues to the c o r r e s -1 5

ponding s ta tes in N . 4 0 4 1

A paper on the Ca (d,p) Ca reac t ion has been sub

mitted to the Physical Review and will be published in the September 1 i s sue . 1

Bonner , K r a u s , Marion, and Schiffer, Phys . Rev. 102, 1348 (1956). E . S, Shire and R, D, Edge , Phil . Mag, 46 , 640 (1955),

26-3 29

26-3 Measuremient of Proton Strength Functions (5220)

Linwood L. L e e , J r . , and John P , Schiffer Reported by John P . Schiffer

1 The complex-potent ial naodel of the nucleus has been

successful in explaining the var ia t ion with atomic weight of the neutron 2

s t reng th function (the average reduced par t ia l width of nuclear energy levels

divided by the i r spacing). A maximum in the S-wave neutron s t rength func

tion is well es tabl ished at AfHSb. A previous s e a r c h from A = 44 to A = 64 3

revea led no cor responding maximum in the S-wave proton s t rength function.

We have extended these measurement s using a different technique and find 4

a maximum at A » 7 5 . Independently of our work , Weisskopf and Margolis

have found that adding a Coulomb cor rec t ion to an in t r ins ic proton potential

wel l , which differs in depth only very slightly f rom that used for neu t rons ,

shifts this maximum from A » 5 5 to about 70,

The yield from (p,n) reac t ions has been used to obtain

proton s t rength functions for 37^ A^ 133. The quantity calculated is defined by

<<v'Av'°)Av=^.hick[^''\[<^' ^ " / SX^ dE]|-^ o

Here Y is the yield from a t a rge t thick compared to the range of the

incident p ro tons , i is the angular momentum, of the incident p ro tons , E is

the threshold energy , S is the r ec ip roca l of the stopping power in atoms

1 Feshbach , P o r t e r , and Weisskopf, Phys . Rev. 96 , 448 (1954),

R. Cote ' and L. M. Bol l inger , Phys . Rev. 98 , 1162A (1955); <* C a r t e r , Harvey , and Hughes, Phys . Rev. 96, 113 (1954);

K a r r i k e r , Marshak , and Newson, Bull. Am. Phys , Soc. 2 , 33 (1957). 3 ~

Schiffer, Davis and P r o s s e r , Bull. Am, Phys . Soc, Z, 60 (1957). 4

B. Margolis and V. F . Weisskopf, Phys . Rev. (to be published).

30 a,Q 1-26-3

- 2 _1 2 cm Mev , Z-nX is the wavelength of the p ro tons , and P =1/A is thei r

i i

Coulomb penetrabil i ty. Measurements on thick ta rge t s of twenty-eight

elements were made using proton energies up to 4 Mev from the Argonne

Van de Graaff acce le ra to r . The "long counter" employed was cal ibra ted against a s tandard RaBe source .

#1 6. id"*

i 4xld'*

2«I0"'* ;7 8 °i°:

-

8°

-- — 8 "

„ _ _ -B

"BLACK NUCLEUS"

VALUE

--.

'Av

ATOMIC WEIGHT

Fig. 8. Graph of { ( Y ^ ) ^ ^ / D > ^ _

vs atomic weight of ta rget nuclide. The severa l points at one value of A indicate de te r minations at severa l bombarding energ ies .

ATOMIC WEIGHT (opp,o«,m«t.)

\ 0 /A.

(cm)

,,„!353r 5 . 0.03

X / T

Fig. 9- Graph of < ( V ) ^ / ^ \ ^ vs X as defined in the figure. B = Ze /R is the b a r r i e r height. The same type of symbols r ep resen t determinat ions at different bombarding energ ies but for the same target nuclide. The sym^bols a r e r e peated for every fourth t a r get element used.

Figure 8 shows the resu l t s of these

measurements . The peak at A;:j; 70

(or % 75 if a cor rec t ion is added

for the incident proton energies) is

in agreement with the calculated

predict ion for an S-wave maximum.

Figure 9 shows the

data with the Coulomb cor rec t ion

included in the absc i ssa . A nuclear ^ , . , - , ^ 1 3 ^ / 3

radius of 1. 45x10 " A c m was

used here as well as in the pene

trabi l i ty calculat ions. A charge

distr ibution of constant density and _ 1 3 1/3

a radius o f l .ZOxlO A cm was

assumed in computing the Coulomb

correc t ion to a 44-Mev intr insic

potential by using the WKB approxi

mation. These assumptions a re

more or less equivalent to those of

reference 4. The curve was calcu

lated by assuming a resonant S-wave

1

strength function and a "black nu

c l eus" s t rength function for P - and

D-wave p ro tons , but neglecting higher

i -values . It is not quite c lear

whether or not the slight indications

1-26-3 1-28-1 31

o£ peaks at A?5{55and ^ 110 and an inc rease at A/4i 130 could be in te rpre ted

as maxima in the s t reng th functions for protons with higher angular momenta.

It is es t imated that the s t rength functions a r e accu ra t e to

be t ter than 50% and that the re la t ive accuracy for most of them is bet ter

than 25%, After allowing for these unce r t a in t i e s , the evidence for a maxi-

num at A /^ 75 is good. The agreement with the independent predic t ions

based on the complex-potent ia l model seems excellent . It would appear

tha t , within the accuracy of the assumpt ions on which the calculat ions a r e

ba sed , the proton and the neutron potentials a r e equal in depth provided

the same rad i i a r e taken for both.

Values of the Coulomb penetrabi l i ty functions have been

computed recent ly on the IBM 650 and will be used to obtain more accu ra t e

values of the s t rength function. It is a lso planned to study the in te rp re ta t ion

of the data in t e r m s of a Saxon potential ins tead of the square well. The

feasibil i ty of such calculat ions is being invest igated. An extension of the

measu remen t s to higher energies for nuclei in the region 90-^ A ^ 150 is

planned in the near future in the hope of observing the expected P-wave

maximum.

A Le t te r to the Editor r epor t ing on these r e su l t s has

been submit ted to the Phys ica l Review and will be published in the July

15 i s sue .

28-1 Angular Corre la t ions in C h a r g e d - P a r t i c l e Reactions (5220)

T. H. Bra id

P repa ra t ions a r e being made to m e a s u r e p a r t i c l e - g a m m a

angular co r re la t ions in reac t ions init iated by pa r t i c l e s f rom the 60- in-cyclo

t ron—-par t icular ly in the ca se of inelast ic proton sca t t e r ing at 10 Mev.

Elec t ronic equipment is s t i l l being built and tes ted .

32 -^-^ 1-33-2 1-35-3 3X

5 2 1-52-15 33-2 The Decay of „ . Fe (8 hours) (5220) 2 6

Bradley Burson and L o r e n C. Schmid Reported by Bradley Burson

This project has been inactive during the past qua r t e r .

Since no further work can be done until sources become available again ,

repor t ing will be suspended t empora r i ly .

35-3 The Decay of 9-Hour Eu (5220)

Bradley Burson and Loren C. Schmid Repor ted by Loren C, Schmid

Seven in t e rna l - conver s ion -e l ec t ron l ines were observed

for this activity in the photographic magnetic spec t rographs . F r o m the

data on the work functions, five of them a r e in te rpre ted as K, Lg , L , M,

and N lines for a 122,1-kev t rans i t ion following K-capture f rom europium.

The difference between the K and L work functions for the remain ing two

lines is cha rac t e r i s t i c of gadolinium. They thus r e p r e s e n t a t r ans i t ion of

3 45,1 kev following beta decay.

An analys is of the b e t a - r a y spec t rum in the 180° be t a -

ray spec t romete r is planned for the future.

52-15 Gamma Rays from F i s s ion Induced by The rma l Neutrons (5220)

Char les M, Huddleston and C a r r o l l C. Tra i l Reported by Char les M. Huddleston

Work is continuing with the new exper imenta l a r r angemen t

consis t ing of a f ission counter and th ree g a m m a - r a y coun te r s . Since the pile

was not operat ing during much of the past q u a r t e r , the p re sen t s e r i e s of m e a s

u rements has not been completed. P r e l i m i n a r y r e su l t s with the new g a m m a - r a y

counter , however , indicate a confirmation of our e a r l i e r findings; i, e. , the

angular co r re l a t ion between gamma rays and fission fragments shows that the

1-52-15 1-55-7 33

1-56-6

23 5 gamma rays from fission of U a r e emit ted preferent ia l ly in the same d i

rec t ion as the light f ission fragment.

55-7 Capture Gamma-Ray Spectra for Neutrons with Energ ies from 0.1 to 10 ev, (5220)

Berna rd H a m e r m e s h , Rauf Nasuhoglu, Sol Raboy, Roy Ringo and C a r r o l l C, T r a i l Reported by Car ro l l C. T ra i l

The l a rge shield for the scint i l la t ion counters is near ing c o m

pletion. The conta iners for boron carbide and paraffin have been at tached to

the cen t r a l lead shield. Four hundred pounds of boron carb ide were used

to fill the sect ion between the lead and paraffin. The paraffin container

will be filled soon.

A dry box containing a lathe and milling machine is now

avai lable . Both sodium iodide c rys t a l s will be packaged in the coming

quar t e r .

56-6 Com^pton-Electron Magnetic Spec t rometer for Neut ron-Capture Gamma Rays (5220)

R i c h a r d s . P r e s t o n

P r e l i m i n a r y designs for the spec t rome te r have been c o m

ple ted , and cost e s t ima tes a r e being p repa red .

4 1-60-15

1-70-15 1-80-15

60-15 7 .7 -Mete r Ben t -Crys ta l Spectrometer (5220)

Be rna rd Hamermesh and Robert K, Smither Reported by Berna rd Hamermesh

During the past q u a r t e r , studies have been made of the

per formance of the l a rge quartz c rys t a l (12 in. x 12 i n , ) , The expected

inc rease in the intensity of the diffracted beam over that obtained with the

4 in, X 6 in, c rys t a l has been observed. In addition a study of the line

widths of gamma rays has been c a r r i e d out. Line widths of l e s s than 10

seconds of a rc have been found. This is to be compared with the value of

13 seconds obtained with the sma l l c ry s t a l . Since the l a rge c ry s t a l i s 4 mm

in th ickness compared with 6 mm for the smal l c r y s t a l , the two a r e subject

to different s t r e s s e s when bent to the same rad ius . The line width a p p a r

ently depends upon the applied s t r e s s .

In addition to the above s tud ie s , the automatic control of

the spec t rome te r by the fringe counting s y s t e m of the in te r fe romete r has

been improved. Tes t s of l o n g - t e r m re l iabi l i ty a r e now in p r o g r e s s .

70-15 Measurements of Nuclear Moments by Angular Corre la t ion (5220)

Victor Krohn and Sol Raboy Reported by Victor Krohn

Because of concentra t ion on work on the s y m m e t r y prop

e r t i e s of neutron decay, this project is t e m p o r a r i l y inact ive .

80-15 Molecular Beam Studies (5220)

William Chi lds , John Dalman and Leonard S. Goodman Reported by William Childs

A cons iderable fraction of the p resen t qua r t e r was devoted

to final adjustment of the new va r i ab l e , permanent magne t s , using a beam of

1-80-15 1-81-3 35

1-90-15

potass ium a toms .

Several open-beam radioact ive runs were made on 50-day

jj^ii4m^ In produced by alpha bombardment of s i lver , and 14-hour Ga . In each

case , the amount of activity collected was too smal l for data taking. Since

the requ i rements of each experiment a re somewhat different, it was decided

to concentrate init ially on the Ga'^, produced in C P - 5 by neutron capture .

Since the gall ium can be more easi ly deflected than the indium in our

appara tus , l a r g e r s l i ts were inse r ted to i nc rease the counting ra te for the

refocussed Ga'^.

AVIDAC calculat ions (of the Zeeman splitting of the hyper -

fine s t ruc tu re of the atomic Pj^ state) were made for the stable gall ium so 2

that it could be used for field cal ibrat ion. Resonances have been observed

for the stable Ga and Ga'^. Measurements on the spin and magnetic m o -

ment of Ga a r e expected soon.

81-3 Review Paper on Deposition of Atomic Beams (5230)

Sol Wexler

The final revis ion of the paper is being made .

90-15 Cross Sections for 14-Mev Neutrons (5220)

H. Casson, L. S. Goodman and L. A. Rayburn Reported by H. Casson and L. A. Rayburn

F u r t h e r modifications have been made in the t ime-of-f l ight

c i r cu i t ry in o rde r to improve the stabil i ty. Time resolut ions (full width at

half maximum) between 3 and 3.5 mi l l imic roseconds a r e now obtained with

excellent daily s tabi l i ty and with no maintenance t ime requ i red in the las t

two months .

34 1-90-15

Some t ime has been spent redesigning the flange on the ion

bottle in an effort to dec rease the t ime spent in the periodic rep lacement of

the tip through which ions leave the ion bot t le . A new tip and clean ion

bottle must be instal led about every six weeks.

ANGULAR DISTRIBUTION OF ELASTICALLY SCATTERED 14-MEV NEUTRONS

Absolute differential e l a s t i c - sca t t e r ing c r o s s - s e c t i o n

m e a s u r e m e n t s have been made at 25 to 30 angular posit ions from 10° to

165° in the labora tory coordinate sys tem for each of the following s c a t t e r -

e r s : Zn, Sn, and Sb. The previously reported^ m e a s u r e m e n t s on Pb and

Bi a re being extended to 165°. The resu l t s on Pb and Bi were repor ted at

the Washington meeting of the Amer ican Physica l Society.^ An attempt is

being made to fit these data using a complex square-wel l potential .

INELASTIC SCATTERING OF 14-MEV NEUTRONS

Time-of-fl ight spec t r a of inelas t ica l ly sca t t e red neutrons

have been obtained at s eve ra l sca t te r ing angles for carbon and copper, using

flight paths of 50 cm and 100 cm. The energy range covered was between

about 1 and 14 Mev. The data a r e in p roces s of evaluation and will be r e

por ted on in the next quar te r ly . It is expected that additional data on these

and other e lements (including aluminum and iron) will be obtained during the

next qua r t e r .

^ ANL-5667, Report 1-90-13, p . 40 and ANL-5698, Report 1-90-14, p . 28.

^ L. A. Rayburn, Bull . Am. Phys . Soc. 2, 233 (April 1957).

^ Feshbach, P o r t e r and Weisskopf, Phys . Rev. 96, 448 (1954).

1-91-15 37

91-15 Neutron Transpor t C r o s s Sections; Angular Distr ibut ion of Scat tered Neutrons (5220)

Raynaond O. Lane , Alexander S, Langsdorf, J r , , and Kineo Tsukada Reported by Alexander S, Langsdorf, J r ,

The e a r l i e r exper imenta l r e s u l t s which were r epor t ed in the

Topical Report ANL-5567 a r e now scheduled for publication in the Phys ica l

Review for August 15, 1957. 6

In this quar te r new data were obtained on Li and na tu ra l L i ,

ni t rogen as Be^Ng , oxygen as BeO, and r e r u n s were made on previously m e a s

ured ma te r i a l s : Be , Cu, Sn, P b , and U. These data were taken with about

100 kev reso lu t ion , f rom 100 kev to 2. 3 Mev, at eight angles equally spaced

from 23 to 144 . The data have not yet been analyzed.

In this new work the c i r cu la r t r a c k (ANL-5609, page 55)

and s teer ing magnet (ANL-5667, page 41) were successfully used. In addi t ion,

a magnetic a l te rna t ing-gradient lens was used to focus the proton beam at the

l i thium ta rge t . The lens worked very well so that over 20|jLa of beam was

used , with essent ia l ly no available b e a m being wasted.

In the near future we expect to measu re ca lc ium and s i l i

con. In the fall we hope to be able to measu re Gd, Sm, and Ce. These should

prac t ica l ly comiplete the survey phase of this p rog ram.

It is of considerable in te res t to m e a s u r e the energy d e

pendence of the efficiency of our neutron counters more accura te ly than it

can be done by compar i son with a "long counter" . In the endeavor to do this

cal ibrat ion ( re la t ively , not absolutely) , we have meaisured the angular d i s t r ibu

tion of sca t te r ing by polyethylene. After co r rec t ions for p lura l sca t te r ing and

sca t te r ing by ca rbon , any deviations in the apparent angular d is t r ibut ion of

hydrogen from that predic ted for isotropy in c e n t e r - o f - m a s s coordinates

should be aiscribable to the energy dependence of the counte rs . The co r r ec t i on

38

31 1-91-15

1-98-14

calculat ions will be difficult. Except for this difficulty, the method seem«

to be a very a t t rac t ive one for flux ca l ib ra t ions , especia l ly in the difficult

region from about 10 kev to 250 kev. It is very different f rom methods being

t r i ed e l sewhere .

98-14 Total Neutron Cross Sections in the Kev Region (5220)

Car l T, Hibdon

E r r a t u m

Equation (4) on page 45 of ANL 5667 (Physics Summary

Repor t , Sep tember -December , 1956) should read

4-> (T - <r . , Y - + 1 / s m i n

((T - a - . ) - («r - o- . ) ( E / E ) " m * m m m s min m ' '

27 Resonances with Al

The complete l i s t of the neutron resonances found with 27

Al in the region from 0 to 415 kev is given in Table V. The values for 28

levels in Al a r e obtained by multiplying the observed resonance energies

by 27/(27 -f 1) to c o r r e c t them to values for the c e n t e r - o f - m a s s sy s t em and 28

then adding 7. 722 Mev, the energy of Al formed by capture of neutrons of

negligible kinetic energy.

98-14 39

2 7 TABLE V. Resonance energies of Al + n and corresponding energy

levels of Al

E r

(kev)

35 .3

84 .5

87

89. 5

89 .8

120

140

143.5

149

152.5

158

178.5

182

190

205

Energy levels of Al^° (Mev)

7.756

7.803

7.806

7.808

7.809

7.837

7.856

7.860

7.866

7.869

7.874

7. 894

7.897

7.905

7.920

r (kev)

208.5

212

216

223

229

233

257

266

271

278

283. 5

288

294

300

306

Energy levels of Al^®(Mev)

7.921

7.926

7.930

7.937

7.943

7,947

7.970

7.978

7.983

7.990

7.995

8.000

8,005

8.011

8.017

r (kev)

308

310

311.8

316

344

366

370

374

384. 8

395

404

407

410 .5

Energy levels of Al^® (Mev)

8. 019

8.021

8.022

8. 027

8. 053

8. 075

8.079

8. 082

8. 093

8. 103

8. I l l

8. 114

8. 118

Only a few of the resonances a r e sufficiently well i s o

lated for it to be possible to get accu ra t e values of thei r p a r a m e t e r s . They

occur mostly in c l u s t e r s . It is possible to make plausible assumpt ions as to

J values and widths that will be in accord with the observed r e s u l t s , but not

unambiguously enough for such r e su l t s to be of much significance.

^o 1-98-14

The fol lowing c o n c l u s i o n s , h o w e v e r , a p p e a r to be

j u s t i f i ed .

(1) Many of t h e 34 o b s e r v e d p e a k s m u s t b e o t h e r t h a n

s - w a v e r e s o n a n c e s , i . e . , m u s t h a v e i v a l u e s g r e a t e r t h a n 0. S ince I for 27

Al i s 3 / 2 , t he p o s s i b l e J v a l u e s for i = 0 a r e 2 and 3. If t h e r e s o n a n c e s

w e r e a l l of one o r the o t h e r of t h e s e two t y p e s , f r e q u e n t d e e p i n t e r f e r e n c e

m i n i m a wou ld h a v e t o o c c u r b e t w e e n a d j a c e n t r e s o n a n c e s h a v i n g t h e s a m e

v a l u e s of J . No i n d i c a t i o n s of the e x p e c t a b l e m i n i m a a r e found. A l s o ,

s e v e r a l r e s o n a n c e p e a k s tha t s t a n d above the b a c k g r o u n d (no t ab ly , t h e o n e s

a t 120, 158 and 257 kev) do not show the a s y m m e t r y c h a r a c t e r i s t i c of r e

s o n a n c e s for w h i c h i = 0 .

(2) The w e l l i s o l a t e d r e s o n a n c e a t 35 . 3 k e v c l e a r l y

s h o w s the i n t e r f e r e n c e d ip and a s y m m e t r y of an s - w a v e r e s o n a n c e . The p e a k

c r o s s - s e c t i o n , e s p e c i a l l y t h a t o b s e r v e d u s i n g s e l f - d e t e c t i o n , i n d i c a t e s t h a t

J = 3 , a l t h o u g h J = 2 h a s not b e e n r u l e d out c o n c l i i s i v e l y . A s s u m i n g tha t

J = 3 , a n a l y s i s by the m e t h o d d i s c u s s e d in A N L - 5 5 6 7 , p , 4 4 , s h o w s t h a t

r = 2. 05 kev .

(3) T h e r e s o n a n c e a t 120 kev i s su f f i c i en t ly w e l l i s o

l a t e d t h a t one c a n be r e a s o n a b l y s u r e f r o m i t s l a c k of m a r k e d a s y m m e t r y

t h a t i t is not a n s - w a v e r e s o n a n c e . The m e a s u r e d p e a k c r o s s s e c t i o n i s 10. 3

b a r n s above the b a c k g r o u n d , and does not i n c r e a s e a p p r e c i a b l y wi th se l f -

d e t e c t i o n . The e x p e c t a b l e v a l u e s for J = 2 and J = 3 a t t h i s e n e r g y a r e 11, 8

and 15. 8 b a r n s , r e s p e c t i v e l y , s o J = 2 s e e m s t o be t h e nnore l i k e l y v a l u e . The

wid th i s c l o s e to 3 kev . T h e c o r r e s p o n d i n g r e d u c e d wid th i s w e l l be low t h e

Wigner l i m i t for i = 1, but t w i c e t h a t for i = 2. F o r t h i s l e v e l , t h e n , i t i s

l i k e l y t h a t J = 2 and i = 1. A p a p e r on t h i s w o r k i s b e i n g p r e p a r e d .

1-102-9 41

102-9 Neutron Cross Section Measurements by the Self-Indication Technique (5220)

F , P, Mooring, J. E, Monahan, A. Langsdorf, J r . , and C. W. Kimball Reported by C. W. Kimball

The m^easured self- indication c r o s s sect ion is defined as

N(r(E), , -M<r(E), s

"• = N

1 / r e - ^ ' ^ ^ ^ ' ( l . e - ^ ^ ^ ' ) R ( E ) d E - i t i j -

/(l.e-^<^hR(E)dE

s where tr - measured apparent self- indicat ion c ro s s sec t ion ,

0-(E) = t rue total c r o s s sec t ion , 2

N = a t o m s / c m of t r a n s m i s s i o n s a m p l e , 2

M = a t o m s / c m of detection s a m p l e ,

R(E) = product of the dis tr ibut ion function of the neutron spec t rum

and the efficiency of the detection sys tem. The t rue total c r o s s sect ion m.ay be expres sed as

(r(E) =0-^(1 + 6(E) ) , a

where 6 (E) expresses the energy dependence of the cross section and o- is a

the average c r o s s sect ion. The moments of 6 (E) a r e

< 6 ' ' ) = / 6 ^ R d E , j = 1,2, . . . ,

^ d E

so that or is defined by the condition /^y = 0, An express ion for the self-

indication c r o s s sect ion in t e r m s of the moments of the energy- dependent 1

par t of the t rue total c r o s s sect ion has been published in the form

1

J. E. Monahan and A. Langsdorf, J r . , Phys . Rev. 98A, 1147,(195^,

42 /Al_ 1-102-9

s 0- = <r - TN

» If M

e ^ « . l

(S^y + TN^ - M (M + Nj , "^a^^^^y + • • [ T 2 e^*^a_i

£1

A p p l i c a t i o n of a n u m e r i c a l m e t h o d t o t h e d a t a o b t a i n e d

f r o m p r e l i m i n a r y e x p e r i m e n t s on Z r i n d i c a t e s t h a t t h e m o m e n t \6 i/

6 y . When cr i s e x p r e s s e d

in p o w e r s of n = Nor and t e r m s a r e kept to t h e o r d e r of \ 6 / > the s e r i e s

b e c o m e s

1 • 2 \ 2 3

Wiere

NT" nn n

and

m a =

e ' " . !

J, E . M o n a h a n , A S t a t i s t i c a l A n a l y s i s of A n g u l a r D i s t r i b u t i o n D a t a (unpub l i shed) , 3

A, L a n g s d o r f , J r , , P h y s i c s D i v i s i o n Q u a r t e r l y R e p o r t , A N L - 5 3 1 7 , p , 43 (unpub l i shed ) .

1-102-9 ^3 1-108-9

It can be seen from the l a t t e r form of the s e r i e s that ^-6 /

must be cons idered to obtain \ 6 / • If \ ^ / ^^^ ^® evaluated, the r e -4

sonance p a r a m e t e r s can be obtained for an isolated r e sonance .

Exper iments using the self- indicat ion technique a r e being

planned using equipment special ly designed for these m e a s u r e m e n t s . The

elements whose c r o s s sect ions a r e to be invest igated have been chosen on

the bas i s of measurement s of the total and sca t te r ing c r o s s sect ion by A.

Langsdorf, Jr , , R, O. Lane , and J. E, Monahan.

4 Langsdorf, Monahan, and Mooring, Phys . Rev. 98A, 1148, (1955).

5

6 F. Paul Mooring, Report 1-16-6 in this Summary Report .

Langsdorf, Lane , and Monahan, (to be published).

108-9 An He Neutron Spect rometer (5220)

F r a n k J. Lynch

1. DETECTOR USING A CERAMIC-TO-METAL BRAZED INSULATOR ASSEMBLY

Several leaks which developed in welds and sea ls in the

vacuum furnace were located and sealed. Cooling coils were b razed to the

outside of the furnace to keep the neoprene and si l icone gaskets cool. The

furnace has proved sa t i s fac tory up to 1300 C. Provis ion has been made to

admit pure H^ into the furnace by pass ing e lec t rolyt ic H^ through a DeOxo

purif ier unit (pal ladium-catalyst) to rernove O and Linde molecular s ieves

(synthetic zeolite) to r emove H^O. For safety r e a s o n s , H^ p r e s s u r e s in

the furnace a r e l imited to 3 c m Hg.

Tes t s were conducted to invest igate the bonding of var ious

1-108-9 1-110-2

braz ing metals to Frenchtown high-alumina c e r a m i c , using Ti and Zr as

active meta ls . Brazing metals t r i ed were Ag, Cu, BT solder (Ag-Cu

eutect ic) , and Au, in the forms of powder , wire and sheet . Successful

bonding was obtained with all metals except Au. Both TiH2 and ZrHg were

sa t i s fac tory as active m e t a l s , but TiH^ appeared to give somewhat more

consis tent r e s u l t s . A mixture of 90% powdered BT solder and 10% powdered

TiHg with Zapon lacquer as binder gave very good r e s u l t s . BT wire with an

8% Ti co re was at leas t as good. The process ing consis ted of baking out and o o

evacuating at 300-400 C , then firing 5 - 1 0 minutes at 1000 C. Oxidation

was reduced by admitt ing H^ when the oven had cooled to 600 C. When Cu

is used , it must be oxygen f ree . When powdered Cu is used , it is f i r s t r e

duced in Hg at about 400 C. F i r ing in Hg was not successful .

The jigs used to hold the par t s in alignment have been r e d e

signed. One sa t i s fac tory sea l has been cons t ruc ted , and another is near ly

completed.

110-2 Storage of Pulse-Height Data on Magnetic Tape (5220)

J a m e s B. Baumigardner and F rank J. Lynch Reported by James B. Baumgardner

Work with the Ampex model 500 tape r e c o r d e r has been

abandoned, owing to the difficulties anticipated in obtaining and maintaining

the per formance c h a r a c t e r i s t i c s r equ i red for this work. A new t a p e - t r a n s

port mechanism has been designed and shop work for this unit essent ia l ly

completed. The machine is being wired and a s s e m b l e d , after which a study

will be made to evaluate the var ious methods of record ing pulse-height data;

i. e. , d i r ec t , FM, and digital . It is believed that s eve ra l of these methods

will find applicat ion, depending on the widely differing r equ i r emen t s in r e c o r

ing data.

1-117-4 1-121-2 45

1-123-2

117-4 M e a s u r e m e n t of N e u t r o n Ha l f -L i f e Us ing a Diffusion Cloud C h a m b e r (5220)

H. B r y a n t , G. C a g l i o t i , N . D 'Ange lo and C. M. Huddle s t on R e p o r t e d by G. C a g l i o t i and N. D ' A n g e l o

The d e t a i l s of the c o n s t r u c t i o n of t h e c loud cham^ber h a v e b e e n

d e s c r i b e d in T o p i c a l R e p o r t A N L - 5 7 4 5 and a s h o r t e r p a p e r d e s c r i b i n g i t s

nove l f e a t u r e s h a s b e e n s u b m i t t e d for p u b l i c a t i o n .

121 - 2 S p i n - M o m e n t u m C o r r e l a t i o n i n t h e B e t a D e c a y of P o l a r i z e d L i s Nuc le i (5220)

M. T . B u r g y , W. C. D a v i d o n , T. B. N o v e y , G. J . P e r l o w , and G. R. Ringo

Since the t i m e and e q u i p m e n t n e e d e d to c o n t i n u e t h i s p r o j e c t

a r e be ing u s e d by the e x p e r i m e n t on t h e s y m m e t r y p r o p e r t i e s of n e u t r o n d e c a y ,

t h i s w o r k is t e m p o r a r i l y i n a c t i v e .

123-2 The S y m m e t r y P r o p e r t i e s of N e u t r o n D e c a y (5220)

M, T . B u r g y , R, J, E p s t e i n ( E l e c t r o n i c s D i v i s i o n ) , T . B , Novey ( C h e m . Div. ) , S. R a b o y , G. R. Ringo and V. L . T e l e g d i (U. of Chicago)

S ince the n e u t r o n i s one of t h e s i m p l e s t e n t i t i e s showing b e t a -

e m i s s i o n , t h e s y m m e t r y p r o p e r t i e s of the d e c a y of the n e u t r o n a r e c l e a r l y

4-L 1-123-2

1 2 3 of in teres t in connection with the recent advances in our knowledge

of the charac te r of beta decay. In an attempt to improve the understanding

of the nature of the neutron 's beta decay, we have measured the re la t ive

probabili ty of be ta -emiss ion by the neutron in the direct ions respect ive ly

para l le l and ant iparal le l to the spin of the neutron.

This measurement was made with the a r rangement shown in

outline in Fig. 10. The neutrons measured were in a t he rma l beam taken

±

BETA COUNTER

(ACTUAL POSITION IS

9" ABOVE PLANE OF

THE SECTION SHOWN)

COBALT MIRROR SURFACE

COPPER MIRROR BACKING

- A L U M I N U M MOUNTING BAR

B e - C u CATHODE

12 INCHES

Fig. 10. Horizontal section through the apparatus used in detecting the decay of polar ized neutrons . The section is taken at the level of the center of the beam. The angle between the beam and the mi r ro r is great ly exaggerated for c lar i ty .

Wu, Ambler , Hayward, Hoppes and Hudson, Phys. Rev. 105, 1413 (1957),

Garwin, Lederman and Weinrich, Phys . Rev. 105, 1415 (1957).

J. L. F r iedman and V. L . Telegdi , Phys. Rev. 105, 1681 (1957).

123-2 47

from the Argonne R e s e a r c h Reac to r , C P - 5 , through a hole 8 5 - 3 / 4 in. long,

1/4 in. wide, and 8 in. high. This beam was polar ized by reflect ion f rom

a 5 in. high m i r r o r of 95% Co and 5% Fe magnetized in a ve r t i ca l d i rec t ion 4

by a field of about 250 o e r s t e d s . At a grazing angle of about 8 minutes 7

the ref lected beam contained a total of 7 x 10 neutrons per sec and was

87 ± 7% polar ized (as de termined by using another cobalt m i r r o r as an

analyzer) . To keep the neutrons in a definite ve r t i ca l or ien ta t ion , a v e r t i

cal field of about 10 gauss was applied to the vacuum chamber in which the

decays were observed. The lead shield in this chamber was made , in p a r t ,

of an alloy including 0. 5% by weight of l i thium to minimize gamma rays

f rom neutron cap ture . The gamma flux left after these shielding m e a s u r e s

was l ess than 100 m r / h r in the beam.

Neutron decays were observed by coincidences between a beta

detector and a proton de tec tor . The beta detector was a plast ic sc in t i l l a

tor 0. 21 in. thick and 5 in. in d iamete r . Pu lses fromi the beta detector were

accepted if they cor responded to an energy loss of 110 to 610 kev. The p r o -5

tons were detected by the method used by Robson and by Snel l , P leasonton 6

and McCord, in which the protons a r e acce le ra t ed to about 12 kev in a

sy s t em that focuses them on the cathode of an e lec t ron mul t ip l ier . In our

case the cathode was an el l ipse of Be-Cu 5 in. long by 4 in. high, act ivated 7

in place by heating to a dull r ed heat by e l ec t ron-bombardment . The r e

mainder of the e lec t ron mult ipl ier was an unces ia ted dynode s t r u c t u r e f rom

a Dunnont 6292 photo mult ipl ier , Annplified pulses from the beta and proton

de tec tors were fed through pulse-height ana lyzers into a coincidence c i rcu i t

M. H a m e r m e s h , Phys . Rev. J5^, 1766 (1949); D. J. Hughes and M T. Burgy , Phys . Rev. 81^ 498 (1951).

J. M. Robson, Phys . Rev. 83 , 349 (1951). 6

Snell , P leasonton , and McCord, Phys . Rev. 78 , 310 (1950). 7

J. M. Robson, Rev. Sci. Ins t r . 19, 865 (1948).

48 1-123-2

in which a coincidence pulse was produced if (a) both proton and beta pulses

were of appropr ia te s ize and (b) the proton pulse a r r i v e d between 0. 2 and

1. 8|xsec after the beta pulse . Moreover , the output of the coincidence c i r

cuit was a pulse of a s ize which was dependent on the delay. This pulse was

fed to a 20-channel pulse-height analyzer which thus gave a display of the

number of coincidences vs the t ime following the beta pulse (up to 1. 8p,sec).

In this display the neutron decays showed quite c lea r ly as a peak near 1 |jisec

de lay—the t ime of flight to the proton counter . About 0.15 coincidence

counts per minute were obtained in a typical measuremen t .

Measurements were made with neutrons polar ized s t ra ight

up and s t ra ight down and with and without a s tee l sh im 0. 010 in. thick placed

at the entrance to the vacuum chamber . This shinn completely depolar izes

a beam of t h e r m a l neutrons and thus gives a null measu remen t for both

field d i rec t ions . The r e s u l t was as follows:

Intensity pa ra l l e l to neutron spin _ A? + n in Intensity an t ipara l le l to neutron spin

When c o r r e c t e d for the solid angle of the beta detector and for the i m p e r

fections of the polar iza t ion (the mean beta veloci ty , ^ v / c ^ , is taken as

0. 80) and expressed in the usual way, the angular dis tr ibut ion re la t ive to

the neutron spin d i rec t ion becom,es

W(e) = 1 - (0. 37 ± 0.11)(v/c) cos e.

The e r r o r given in th is r e su l t is a lmos t ent i re ly due to the s ta t i s t i ca l

fluctuations in the nneasurements . The es t imated uncer ta in t ies in the c o r

rect ions make a very sma l l contribution. 1 2 3

In view of the developments r e f e r r e d to e a r l i e r ' the beta

decay of the neutron is to be descr ibed by 8 p a r a m e t e r s (some or a l l of which

may be complex if t i m e - r e v e r s a l invar iance fails) . It may be of i n t e r e s t .

123-2 Jl, 1-125-1

however , to compare the present r e su l t with the predict ions of some s imp l i

fied var iants of the genera l theory which have been proposed.

8 (1) Two-component neutrino theory -0 , 08 or -1 , 00

9 l O

(2) Twin-neutrino theory -0 , 54 1 1

(3) Pa r i ty conservat ion in F e r m i in teract ions -0 , 22 or -0, 87

In all these predict ions it is a s sumed that

^^ sum of squares of G - T coupling constants ^^ ~ sum of squares of F e r m i coupling constants

In the predict ions giving two values of the coefficient, the f i r s t co r responds

to X 0 and the second to x S 0, It should be noted that in the event of fa i l

ure of t i m e - r e v e r s a l invar i a n c ^ the G T - F in te r fe rence t e r m in the two-

component neutr ino theory might be reduced to make the theory consis tent

with the p resen t measurement ,

A r epo r t on this work has been submit ted for publication.

8 T. D. Lee and C, N. Yang, Phys . Rev, 105, 1671(1956). See a lso L,

Landau, Nuclear Phys . 3 , 127 (1957) and A. Sa lam, Nuovo cimento, 5 , 299 (1957). 9

M, A. P r e s t o n , Can. J, Physics (in p r e s s ) . 1 0

M, G. Mayer and V. L. Telegdi , Phys . Rev, (in p r e s s ) . 1 1

Alder , Stech and Winther, Univers i ty of I l l inois , unpublished r e p o r t .

125-1 Polar iza t ion of Pos i t rons Demonst ra ted by Annihilation in Magnetized Mater ia ls (5220)

S. S. Hanna and R, S. P r e s t o n Reported by R. S. P r e s ton

I. ANNIHILATION IN IRON

1 In studies of the conservat ion of par i ty in weak i n t e r ac t i ons .

T. D. Lee and C. N. Yang, Phys . Rev. 104, 254(1956).

the longitudinal polar izat ion of beta par t i c les f rom unpolarized sources has 2 - 5

been measured by seve ra l methods. In the p re sen t investigation a

method has been developed for measur ing the polar iza t ion of pos i t r ons , and 6 4

the polar izat ion of posit ive beta par t ic les from Cu has been observed. 6 4

A direc ted beam of pos i t rons f rom a Cu source impinged

on the end of a cyl indr ical sample 4 mm in d i a m e t e r , and the two-quantum

yield was detected with two Nal counters placed 180 apar t and operated in

coincidence. Appropr ia te shielding suppres sed radia t ion f rom posi t rons

annihilating anywhere but in the i ron sample . The sample was mounted in

a magnetic field which could be made ei ther pa ra l l e l or an t ipara l le l to the

di rect ion of the posi t rons and hence to the p r e sumed polar izat ion.

One coun te r , at a dis tance of 290 c m , had an a p e r t u r e of - 6

9 X 10 s t e r ad i ans . The second coun te r , at a dis tance of 165 c m , was un-_ 3

coUimated and subtended an angle of 3 x 10 s t e r ad i ans . In order to ob

se rve the angular co r re l a t ion of annihilation rad ia t ion , cyl indr ica l lead

a b s o r b e r s of success ive ly increas ing d i ame te r s were inse r t ed in front of,

and coaxial with, the uncoUimated counter . A measu remen t of the angular

co r re l a t ion for annihilation in copper , obtained with this technique, ag reed 6

sa t i s fac tor i ly with the r e s u l t of Lang et a l .

A lead absorbe r was se lec ted which effectively ecl ipsed the

cen t ra l cone (half-angle equals 8. 5 mil l i radians) of the angular d is t r ibut ion

for i r on , allowing observat ion of the "wings" of the dis t r ibut ion cor responding

to annihilation in the sample by e lec t rons of high momentum. The yield so 2

Frauenfe lde r , Bobone, von Goeler , Levine , L e w i s , Peacock , R o s s i , and De Pasqua l i , Phys . Rev. 106, 386 (1957). 3

Lorne A. Page and Milton Heinberg , Phys . Rev. 106, 1220 (1957). 4

Lorne A. Page and Fe l ix E. Obenshain, Bull. Am. Phys . Soc. 2, 260 (1957). 5

Frauenfe lde r , Hanson, Levine , R o s s i , and De Pasqua l i , Phys . Rev. (in p r e s s ) . 6

Lang, De Benedet t i , and Smoluchowski, Phys . Rev. 99 , 596 (1955).

125-1 51

obtained was normal ized to the total intensity with the absorbe r removed.

With fields producing sa tura t ion in the i ron s a m p l e , this normal ized yield

N was consis tent ly higher by (5 ± 1)% when the field was pa ra l l e l than when

it was ant ipara l le l to the di rect ion of motion of the pos i t rons . The effect

vanished when a copper sample was used. Geometr ica l effects were inves t i

gated by r eve r s ing the di rect ion of the pos i t rons and the r e su l t s were not

significantly different. A further check on the exper imenta l a r r angemen t

was obtained by performing the exper iment with f i rs t one half and then the

other half of the l a rge counter covered with a lead shield. In both ca se s the

s ame effect was obtained. The ra t io N obtained for copper is higher than

for i ron , in agreement with re fe rence 5.

A plausible explanation of the above r e su l t may be s u m m a r i z e d 6 4

as follows: (1) Pos i t rons emit ted f rom a Cu source (spin change 1 —>• 0) a r e par t ia l ly polar ized pa ra l l e l to the i r d i rec t ion of motion, i. e. , opposite

1 to the di rect ion observed for negative e l ec t rons . (2) At the t ime of the i r

annihilation the posi t rons s t i l l r e t a in a subs tant ia l amount of this p o l a r i z a

tion. (3) Annihilation in i ron takes place predomiinantly in the region mid

way between nuclei where the d-e lec t rons mainly respons ib le for f e r r o -

miagnetism have higher momentum than the s - e l e c t r o n s . (4) Thus when the

field is pa ra l l e l (e lectron spin ant iparal le l ) to the pos i t ron sp in , two-quantum

annihilation is enhanced in the h igh-momentum region of the angular c o r r e

la t ion, and when the field is r e v e r s e d it is diminished.

A r epo r t on this work has been published as a Le t te r to the

Ed i to r , Phys . Rev. 106, 1363-1364 (June 15, 1957).

I I . ANNIHILATION IN MATERIALS OTHER THAN IRON

64

In further s tudies of the pos i t rons f rom Cu , the samples in

which the annihilation occurs have been made of ma te r i a l s other than i ron .

Also , it has been possible to fil ter out varying amounts of the low-energy p a r t

1-125-1

52^ of the posi t ron spec t rum by inser t ing different th icknesses of aluminumi

6 4

foil between the Cu source and the sample . For al l of the m e a s u r e m e n t s ,

the magnetic field, the s ize of the s a m p l e , and the angle ecl ipsed by the

Pb absorber were kept constant .

Table VI s u m m a r i z e s r e su l t s obtained so far . F e , Co and

Ni a r e fer romagnet ic in varying deg rees . Cu is not fe r romagnet ic , and

Gd is fer romagnet ic at t e m p e r a t u r e s below the Curie point, 16 C. The

different r e su l t s among the fer romagnet ic ma te r i a l s ref lect not only the

gross differences in fer romagnet ic p r o p e r t i e s , but also differences in

the details of the angular co r re la t ions of the annihilation photons. These

details depend on the momentum dis t r ibut ion of the e lec t rons which can be

aligned in a magnetic field and which can annihilate with the rma l i zed p o s i

t rons .

TABLE VI. Values of (N, - N_)/N in pe r cen t , for var ious

samples as a function of thickness of abso rbe r .

Sample 0

Thickness of a luminum absorbe r (mils) 4 8 12 16

Co 5.4 ± 0 . 8 6. 0 ± 1.0

Fe(s teel) 3.2 ± 1. 0 6. 0 ± 1. 1

Fe(Armco)

Ni - 0 . 3 ± 0 . 9 -0 . 1 ± 1.0

Cu

Gd (T=20°C)

Gd(T=-180°C)

0.5 ± 1. 2

9 .4 ± 1 . 2

8. 0 ± 1.4

0. 1 ± 1. 2

2, 2 ± 2 ,9

0. 0 ± 0. 6

11 + 1.9 11 ± 2 .5

-1 1-138-4 5;

1-139-7

It is seen in the table that Co and Fe show the g rea te s t effect.

The l e s s s t rongly fer romagnet ic Ni and the complete ly non-fer romagnet ic

m a t e r i a l s , Gd at r oom t e m p e r a t u r e and Cu, show li t t le or no effect. Gd

cooled to -180 C by liquid ni t rogen is s t rongly fer romagnet ic but no effect

is obse rved , so that the behavior of its "magnet ic" e lec t rons must be quite

different f rom that of the cor responding e lec t rons in Co and Fe .

The polar izat ion of the posi t rons at the t ime of annihilation

is expected to be prac t ica l ly equal to v / c , the value at emiss ion . The in

se r t ion of additional a luminum foils to absorb the slower pos i t rons se lec ts

the pos i t rons emit ted at higher veloci t ies . The cor responding i nc r ea se in

polar izat ion with inc reas ing thickness of a luminum foil was observed and

is best i l lus t ra ted in the table by the sequence with the cobalt s ample .

138-4 Cha rac t e r i s t i c s of Multiplier Phototubes (5230)

Warren L. Buck and Rober t K. Swank Repor ted by Robert K. Swank

No further exper imenta l work has been done. The r e s u l t s

will be published as sQon as the ca l ibra ted phototube is rece ived and the

few measurement s remain ing can be made.

139-7 Liquid Scinti l lators (5230)

War ren L. Buck and Robert K. Swank Reported by War ren L. Buck

Prev ious r epo r t s on this project have p resen ted in forma

tion on the re la t ive scint i l la t ion efficiencies of var ious organic liquid

1-139-7

solut ions. ' ' While most of the solutions studied employed toluene as

the solvent , a few solutions employing p-xylene , t r i e thy lbenzene , or

phenylcyclohexane were included. On the bas i s of these studies it was con

cluded that toluene is the most general ly useful solvent for liquid sc in t i l

l a t o r s .

More recent ly an invest igat ion has been made of sc in t i l l a

ting solutions with isopropylbiphenyl as solvent. In view of the favorable

per formance of these so lu t ions , it is felt that the poss ibi l i t ies of using

this solvent should be brought to the attention of persons in te res ted in

counting with liquid sc in t i l l a to r s .

The isopropylbiphenyl used in this study was obtained from

Monsanto Chemical Company, St. L o u i s , Missour i , as a t echn ica l -g rade

mixture composed of approximate ly 62% meta- and 38% p a r a - i sopropylb i

phenyl. The manufacturer s ta tes that the ma te r i a l has a boiling range of o o

295-300 C and a pour point of -54 C. It was vacuum-dis t i l l ed twice before

u s e , no at tempt being made to s epa ra t e the i somer i c components .

Data on the var ia t ion of the output of scint i l la t ion light

with the concentrat ion of the solute were obtained for isopropylbiphenyl

solutions of p- te rphenyl ( p - T P ) , diphenyloxazole (PPO) , and phenylbi-

phenylyl-oxadiazole (PBD) with both a i r - s a t u r a t e d and argon-bubbled solu

t ions . The r e s u l t s , along with data on cor responding toluene so lu t ions ,

a r e s u m m a r i z e d in Table VII.

It is noted that while the argon-bubbled isopropylbiphenyl

solutions have nea r ly the s ame efficiencies as the cor responding toluene

1

Physics Division Summary Repor t , ANL-5554, pp. 76-95 (unpublished). 2

Physics Division Summary Repor t , ANL-5609, pp. 67-75 (unpublished). 3

Physics Division Summary Repor t , ANL-5698, pp. 50-55 (unpublished).

sf-

55

solu t ions , the quenching effect resul t ing from dissolved oxygen is l e s s in the

isopropylbiphenyl solut ions. Thus when a i r - s a t u r a t e d solutions a r e employed,

the use of isopropylbiphenyl as solvent r e su l t s in somewhat g rea te r yields of

photons , especial ly when PPO is used as the solute.

TABLE VII. Relative light outputs of some liquid sc in t i l l a to r s .

Relative photon yield Air : a rgon Solvent Solute (g/1) a i r argon ra t io

p - T P (5) 1. 03 1. 29 0. 80

Isopropylbiphenyl PPO (5) 0.95 1.10 0.86

PBD (9) 1. 05 1.21 0. 87

p - T P (5) 0,98 1.29 0. 76

Toluene PPO (5) 0.82 1.08 0.76

PBD (10) 1. 00 1.23 0. 81

Determinat ions of the quenching resul t ing f rom addition

of d iphenylmercury revea led that this effect a lso is l e s s s e v e r e in i sopropyl

biphenyl solutions than in the corresponding toluene solut ions. For example ,

addition of only 9 g/1 d iphenylmercury to a toluene solution containing 5 g/1

PPO produces a 50% reduct ion in photon yield, while 38 g/1 of the mercu ry

compound a r e requ i red to achieve the same degree of quenching of the light

output with the cor responding isopropylbiphenyl solution. This apparent ly

g rea te r immunity of isopropylbiphenyl solutions to quenching effects is con

s ide red to war ran t further study.

At room t empe ra tu r e isopropylbiphenyl has a density

^ 1 3 % grea te r than that of toluene. The resu l t ing inc reased density of atomic

e lec t rons in isopropylbiphenyl solutions should give a significantly l a r g e r

1-139-7 1-142-9

c r o s s section for the Compton sca t te r ing p r o c e s s . This fact , together with

the possibi l i ty that significant amounts of me rcu ry or other heavy elements

can be incorporated in isopropylbiphenyl solutions without causing prohibi

t ively great quenching, should be of in te res t to those concerned with the

application of liquid sc in t i l la tors to the detection of gamma r a y s .

Exper ience has shown that a se r ious fire hazard may r e su l t

f rom the use of l a rge volumes of liquid sc in t i l l a to r s . In this r e spec t i s o

propylbiphenyl offers an advantage in that it has a re la t ive ly high flash point o o o

of 139 C (compared with 5 C for toluene and 25 C for p-xylene) and ve ry

low volatili ty at room t e m p e r a t u r e . During an exper iment conducted to

de te rmine re la t ive r a t e s of loss by evaporat ion at r oom t e m p e r a t u r e , a s a m

ple of isopropylbiphenyl suffered less than 0.1% loss while s ini i lar samples

of toluene and p-xylene showed losses of 52% and 20% respec t ive ly . The

low volatili ty of isopropylbiphenyl should contr ibute both to the safety and to

the convenience of its use .

It is noted that when cooled to the t empe ra tu r e of d r y - i c e

isopropylbiphenyl is a t r an spa ren t glassy sol id , whereas toluene r ema ins a

liquid and p-xylene f reezes as a mul t icrys ta l l ine m a s s . Poss ib le ways of

exploiting this behavior of isopropylbiphenyl at low t e m p e r a t u r e s in con

nection with scint i l la t ion counting have been suggested but have not yet been

invest igated exper imenta l ly .

142-9 E lec t ron Acce le ra to r (5220)

Robert K. Swank

The test ing of this device has been completed. The or iginal

design and const ruct ion of the e lec t ron acce l e r a to r and the pulsing c i rcu i t s

were completed about one year ago by Dr. H. B. Phi l l ips . Since then the

142-9 57

presen t author has been respons ib le for the development of the detection equip,

ment and the test ing of the complete sys tem. Although further improvements

in the sys t em a r e feas ib le , and will undoubtedly be made in the fu ture , it

appears that the p resen t per formance of the machine is good enough to p e r

mit accura te measurements of near ly all known sc in t i l l a to r s . The p e r

formance of the sys t em at the p resen t t ime is outlined below:

A. E lec t ron acce le ra to r

1. maximum e lec t ron energy = 100 kev

2. peak cu r ren t = 10 p,a - l o

3. minimum pulse width =10 sec 4. thickness of window = 0. 000 07 inch (nickel)

9

5. energy in pulse of minimum length 'V lO ev.

6. es t imated energy loss in wi ndo-w " 50%

7. r a t e of energy dissipat ion in scint i l la tor = 5000 Mev/m|jLsec

B. Detector

1. photo mult ipl ier - 1P28

2. optical efficiency ' ^ 5 %

3. sp read of t r ans i t l ines in mult ipl ier

(s tandard deviation) '^ 0. 3 m|jisec

4. t ime constant (RC) of anode c i rcu i t ^^0.7 m|j, sec

5. r i s e t ime of pulse in cable - •^ 0. 1 m|jL sec

6. r i s e t ime of osci l loscope «^ 0. 2 m|jLsec

The t ime re sponse of the whole s y s t e m exclusive of the sc in t i l

la tor is essent ia l ly that of the anode c i rcu i t of the photo mult ipl ier . Under

these c i r c u m s t a n c e s , mean lifetimes ^ 1.4 mp,sec can be measu red with con

s iderab le accu racy , and those down to 1. 0 mi|i,sec can be measured to an accur

acy of ^^10%. P r e l i m i n a r y measuremen t s indicate that the commonly-used

sc in t i l l a tors have mean l i fe t imes g rea te r than 2. 0 m|jLsec. Reducing the t ime

58

s? 1-142-9

constant of the anode c i rcui t would requ i re construct ion of a special

photo multiplier . Mere reduction of the load impedance below the presen t

value of 75 ohms resu l t s in an underdamped response . Although the con

struct ion of a special photo multiplier is feas ib le , it is not expedient now

for tw o r ea sons :

IP 28 PHOTOMULTIPLIER

140 4 .001 T K

.oi+fi

7 ^ PC

600 K -^Mf, o —500 to — 3 0 0 0 V

240 j K .001 , .

•01 T K .01 2 4 0 i

.01 i^ jo^

360 ; K

-+0,

- f D j -+D,

-^ I>4 A - + 0 . h '..10=

H ^ ^ ~

.001 Ht-

^

Lj H Lt Q o

Fig. 11. Circuit d iagram of detector c i rcui t used with the e lect ron acce le ra to r . Res is tances a re in ohms and capacitances in microfarads ; L-j and L2 a re lengths of RG-63U cable with t r ans i t t imes of 20 m|a.sec and 40m|uisec respect ively; H is a helix of the EG & G travel ing-wave osc i l loscope; Pc is the photo-cathode; D^ , D2 , etc. , a r e dynodes; and A is the seventh dynode used as the anode of the photo-multiplier .

(1) The p r e s e n t p e r

f o r m a n c e of t h e s y s t e m a p p e a r s

to be a d e q u a t e for m o s t w o r k .

(2) The next im

provement should be the radica l

step of making the measurement

inside the phototube instead of

bringing out an e lec t r ica l signal.

A brief study of severa l methods

of doing this indicates that a t ime - 1 1 _ i o

resolut ion of 10 to 10 gee

may be achieved.

Since any basic

changes in the sys tem appear to

be far in the future, the present

project will be te rmina ted with

this repor t .

A d iagram of the de

tector c i rcui t is given in Fig. 11.

Decay plots of two liquid sc int i l

la tors a re shown in Fig. 12.

1-142-9 1-143-9

59

Fig. 12. Decay of luminescence of two scinti l lating solutions of PBD in toluene after excitation by an impulse from the electron acce le ra to r . In the upper c u r v e , the decay of luminescence is dominated by energy t r a n s fer from solvent to so lu te , and in the lower c u r v e , the decay is cha rac te r i s t i c of the solute.

143-9 Plas t ic Scintil lators (5230)

Louis J. Basi le

1 In a previous repor t mention was made of some

studies concerning the effect that the t empera tu re of polymerizat ion has

on the light output of plast ic sc in t i l la tors . Results which were repor ted

showed that samples which were polymerized at a higher t empera tu re

had a higher light output. 2

More recent ly Shimizu et al. have published r e

sults on their studies on polystyrene- terphenyl sc in t i l la tors . They in

vestigated the efficiency of plastic sc int i l la tors as a function of the degree

of polymerizat ion. Samples of p - te rphenyl - s ty rene solutions were poly-

1

Physics Division Summary Repor t , ANL-5609, p. 81. 2

S. Shimizu, F . Hi rayama, and S. Okamato, Annual Report on the Resea rch Application of Artificial Radioactive Isotopes in Japan, Vol. 3 , (1956).

TOLUENE 4^0.2g/jl PBD

T» 5 .59 m^ «

'°^, °%o.

TOLUENE'*- I O g / £ PBD

T " 2 . 0 6 cn/t»

4 6 8 10 T I M F in m II %mc

12 14

1-143-9 ^C? 1-145-2

mer ized at different t e m p e r a t u r e s , sho r t e r heating t imes being used at o

higher t e m p e r a t u r e s . For example , at 190 C the samples were heated for o

a period of 4 h o u r s , as compared to 8 days at 100 C. The degree of poly

mer iza t ion was obtained by viscosi ty measu remen t s . Resul ts show that

for low solute concen t ra t ions , polymeriz ing the samples at a lower t e m

p e r a t u r e produces a sc int i l la tor having a higher light output. Using thei r

da ta , the authors propose a scheme of energy t ransfe r which involves the

polymer chain.

We have decided to invest igate this p rob lem more tho r

oughly. Tentative plans a r e to polymer ize samples for different per iods of

t ime at each of s e v e r a l different t e m p e r a t u r e s . The average molecular

weight of the polymerized samples will be 'de te rmined by re la t ive m e a s u r e

ments of the viscosi ty of a solution of the polymer .

During the pas t qua r t e r most of our efforts have been

d i rec ted toward obtaining and cal ibra t ing the v i scomet r i c equipment. In

p r e l im ina ry work on one phase of the p rob l em, samples of p - t e rpheny l -

s tyrene and PBD-s ty rene have been polymer ized at 110 C. The durat ion of

heating was var ied from 50 to 200 hours . Results show that as the heating

t ime i n c r e a s e s , the light output i n c r e a s e s and in some cases goes through

a maximum. Samples po lymer ized for shor t t imes show marked c r a z i n g ,

indicating incomplete polymerizat ion.

145-2 Handbook of Nuclear Ins t ruments and Techniques (5230)

R. K. Swank

A contr ibut ion was made on Chemical Dos ime te r s .

7 61

149-7 Dynamic Condenser Magnetometer (5220)

Bradley Burson and Loren C. Schmid Reported by Bradley Burson

As descr ibed in the previous r e p o r t , the dynamic condenser

was d i sassembled in o rde r to rebuild the ro tor sec t ions . This was done

(1) to inc rease the mechanical s t rength and (2) to improve the wave form.

The work is complete and the ins t rument r e a s s e m b l e d and r e s t o r e d to

operat ion.

Each of the three rotor sect ions consis ts of eight p la tes .

These were previously welded together by running a bead of a luminum along

the hub connecting the plates and space r s together at thei r edges . Apar t

from the unsat isfactory outcome of this technique as evidenced by a broken

weld, the method was not feasible with the new plate design. The new sect ions

a r e pinned together by four s ta in less s tee l rods which pass through the plates

and s p a c e r s , and a r e welded at the ends to the col lets which a r e at tached to

each end of the sect ion. Only exper ience in use will show the re l iabi l i ty of

this pa r t i cu la r choice of design.

Two changes were made in the shape of the plates t hemse lves .

To reduce fringing effects , the sect ion near the shaft was extended to in t e r

leave slightly at all t imes with the s ta tor p la tes . This change slightly in

c r e a s e d the minimum value of the capaci tance of the ro tor to ei ther s ta tor

in the "out" posi t ion, but r emoves the sha rp discontinuity inherent in the

ea r l i e r design. F u r t h e r , a smal l e r r o r was found to have been made in the

or iginal function from which the shape of the plate was computed. A new t e m

plate was made in o rde r to rectify this e r r o r .

The r e su l t s of the modifications have justified the effort of

making them. The total harmonic content p re sen t in the output s ignal has

been reduced by more than a factor of two. The total harmonic content is now

less than 3% of the 30-cycle fundamental. Quantitative measu remen t s were not

1-149-7

made on the individual components , but f rom osci l loscope p a t t e r n s , it is

apparent that the 90-cycle component is s t i l l the prevalent consti tuent .

The b e t a - r a y spec t romete r is now being used and a number

of spec t r a have been run. An at tempt is being made to es tab l i sh expe r i

mentally that the magnetometer controls the spec t rome te r in a l inear

fashion throughout its designed range .

An investigation of the Public Service Company's r e c o r d

and reputat ion has shown that deviations in frequency of the o rde r of f rom

3 to 10 pa r t s per ten thousand might occur . Since var ia t ions of this magni

tude can appreciably influence the measuremen t of the intensi t ies of in

t e rna l convers ion l i n e s , a s tabi l ized 60-cycle generator is being cons t ruc ted

to drive the synchronous motor.

As soon as the calibration is comple te , the r epo r t will be

submit ted for publication.

II-18-7 II-19-1

63

11. MASS SPECTROSCOPY

18-7 Lead Agefr of Meteor i tes (5220)

David C. Hess and Royal Marsha l l* Reported by David C. Hesa

Several samples of lead f rom meteor i t es have been measured .

The most in te res t ing data were expected f rom lead ext rac ted f rom t ro i l i t e ,

(sulfide phase) taken from the Toluca (iron) meteor i t e . It was hoped that

this lead would r e p r e s e n t p r imeva l lead s ince it should have been sepa ra t ed

f rom uran ium and thoriunn compounds in the formation of the body. The

r e su l t s showed a l a rge amount of lead , which appeared a lmos t no rma l .

Since t h e r e is much more lead than expected, it must be suspected that

the sample was contaminated with ord inary lead at some t ime before its

analysis-.

* Enr ico Fernni Institute of Nuclear Studies.

19-1 Measurement of Silver from the Tro i l i t e Phase of a Meteor i te

(5230) David C. Hes-s and Royal Marsha l l* Repor ted by David C. Hess^

At the suggest ion of Dr. H. C. Urey , s i lver was ex t rac ted f rom

the t ro i l i t e (sulfide phase) of the Toluca (iron) me teor i t e . If the or iginal

condensat ion and separa t ion into the s i l i ca t e , i ron and sulfide phases took

place within a few million ye a r s after nuc leogenes i s , a possible fract ionation

of Pd and Ag between these phases (e. g. , Pd might be concent ra ted in the 1 107 1o9

i ron phase ) could cause the ra t io of Ag to Ag to vary f rom one phase

* Enr ico F e r m i Institute of Nuclear Studies

1 E. Goldberg, A. Uchiyama and H, Brown, Geochim. et Cosmochim. Acta 2 , 1 (1951).

Lf II-19-1

II-20-3

1 0 7 to another as a resu l t of the beta decay of Pd with a half-life of about

6 a

7 X10 y e a r s .

The yield of s i lver f rom 18. 4 gm of t ro i l i t e was no more than

30 m i c r o g r a m s . The s i lver dithizonate was conver ted to s i lver n i t r a t e , pa r t

of the sample was placed on a tungsten filament and a sma l l amount of boric

acid was added. The filament was heated to dry the sam^ple and the a s s e m b l y

was placed in the mass s p e c t r o m e t e r . 1(37 l o 9

The Ag /Ag ra t io observed ag rees within exper imenta l e r r o r

with the ra t io obtained from a sample of j e w e l e r ' s s i lve r .

2 P a r k e r , C r e e k , Herber t and Lantz r epor t ed by Hol lander , P e r l m a n and

Seaborg , Revs . Modern Phys . 25 , 469 (1953).

20-3 Tr i t ium Age Measurements of Meteori tes (5220)

F r e d e r i c k B e g e m a n n , * ' ' Johannes Ge i s s* and David C. Hess Reported by David C. Hes-s

The work previous ly r epo r t ed by F . Begemann, Johannes

Geiss and D. C. Hess is scheduled for publication in the Phys ica l Review, 1

July 15, 1957. An abs t r ac t was given in e a r l i e r r e p o r t .

Since the previous work was concerned with a single s a m p l e , it

was felt that more recen t meteor i tes should be studied if poss ib le . A

sample of a r ecen t (1952) fall has become avai lable but rrjeasurements have

not yet been made on the sample .

die

Enr ico F e r m i Insti tute of Nuclear Studies. Now at Physikal i sches Inst i tut , Universi ty of Bern]-

1

Physics Division Summary Repor t , ANL-5667, p . 71.

II-28-2 n-29-9 65

28-2 Kinetics of Chemical Reactions in the Gas Phase (5230)

Joseph Berkowitz* and William A. Chupka Reported by William^ A. Chupka

No work has been done on this project pending del ivery of a

monochromator and const ruct ion of a more efficient source chamber for

t he maaa apec t rome te r .

Universi ty of Chicago.

29-9 Gaseous Species in Equi l ibr ium at High T e m p e r a t u r e s (5230) *"

Joseph Berkowi tz ,* William A. Chupka and Mark G. Inghram Reported by William A. Chupka

The mass spec t rome t r i c technique descr ibed in previous r e -1

por t s has been used in the study of the vaporizat ion of be ry l l ium oxide,

u ran ium oxide and a luminum carb ide .

I. BERYLLIUM OXIDE

A bery l l ium oxide cruc ib le was placed inside a tan ta lum Knud-

sen cel l and heated to t e m p e r a t u r e s up to about 2250°K. The effusing

v a p o r , as analyzed by the mass s p e c t r o m e t e r , was found to cons is t most ly

of BeO molecules . The vapor p r e s s u r e was measu red to be about 4 x 10

a tmos at 2223 K and the heat of vaporizat ion was calcula ted to be AH

= 167 kca l /mo le . This yields a d issocia t ion energy of D ° = 4. 9 ev for

the BeO molecule.

II. URANIUM OXIDE

Uranium dioxide was vapor ized f rom a t an ta lum Knudsen cel l

Univers i ty of Chicago. 1

W. A. Chupka and M. G. Inghram, J. Phys . Chem. 59, 100 (1955).

a and the vapor was analyzed mass spec t romet r i ca l ly . At the beginning of

the run the vapor consis ted of about 70% UOg(g) and about 30% UO (g).

However , the intensity of the UOg dec reased steadi ly with t ime by well

over an o rde r of magnitude. This behavior is explained by the fact that

the u ran ium dioxide, as init ial ly loaded into the c ruc ib l e , contains excess

oxygen corresponding approximately to the formula UOg ^. As the sample

is vapor ized , the composi t ion changes to give UOg which then further

evapora tes without change in composit ion. When the composi t ion of the vapor

had apparent ly become cons tant , a sma l l amount of UO was also detected.

A very crude equi l ibr ium constant was measu red for the reac t ion :

2UO„ (g)->-UO (g) + UO„ (g). The entropy of the gaseous spec ies was c a l -

culated f rom es t imated molecular cons tan t s . The AH of the above reac t ion o

was then calculated to be about +30 k c a l / m o l e .

A s e a r c h was made for higher polymers of UOg in the vapor .

None was conclusively found and an upper l imi t of about 1 pa r t in 10 million

was set for the d i m e r , t r i m e r and t e t r a m e r . This i s in contradict ion to the 2

postulate of Acker man , Gilles and Thorn that a d imer Ug O (g) forms a

l a rge fract ion of the vapor at high t e m p e r a t u r e s . It appears possible to

r e - i n t e r p r e t thei r data in t e r m s of apprec iable amounts of UO, UOg and

perhaps other species in the vapor .

The above data yield a crude value for the sum of the bond e n e r

gies of UO and UO^ . This value is about 27. 5 ev. In the light of previous

r e su l t s with other mo lecu le s , we es t ima te that the bond energy of UO will

be sl ightly g rea te r than one-half that of UOg which is given as 14. 4 ev by

Acker man, Gilles and Thorn. Thus , we es t ima te the d issocia t ion energies

of UO and UO to be roughly 7. 5 and 20. 0 ev, respec t ive ly . Fu r the r work

employing reducing and oxidizing conditions should allow accura t e de t e rm i na

tion of t he se va lues .

2 Acker man , Gilles and Thorn , J. Chem. Phys . 25 , 1089 (1956).

67

III. ALUMINUM CARBIDE

Mixtures of a luminum and carbon were evaporated from a

Knudsen cel l and the vapors were analyzed mass spec t romet r i ca l ly . The

vapor cons is t s predominantly of Al atoms with about 0.1% of AlgCg mole

cules . A thermodynamic calculat ion based on our data for the reac t ion

C(s) + Al(g) —• 1/2 Alg Cg (g) yields AH ° = - 16. 5 k c a l / m o l e . T h e r m o

dynamic functions for A]2C2(g) were calculated assuming a l inear AlCg Al

configuration and using es t imated vibrat ional f requencies . Taking the heat

of subl imat ion of Cg as 190 k c a l / m o l e , the energy of dissociat ion of AlgCg

into 2 Al(g) + C2(g) is calculated to be 223 k c a l / m o l e . It is in te res t ing to

note the s i m i l a r s tabi l i ty of the Alg O molecule (atomization energy = 254

kca l /mole ) . This suggests a s imi l a r i t y of behavior between Cg and O,

analogous to the behavior of CN (with one more e lec t ron than Cg) as a

pseudo-halogen. Since Cg has a much higher e lec t ron affinity than C or

C one may expect Cg to form more stable meta l carb ide molecules . T h u s ,

our r e s u l t s suggest that where the act ivi ty of ca rbon is near uni ty, the most

likely metal carbide molecules should be d ica rb ides . ( ^ ( /

34-13 A4 0 - K4 0 Dating of Meteor i tes (5220)

Pe te r E b e r h a r d t , * Johannes Geiss*^' and David C. Hess Work Reported by David C. Hea«

The work previous ly r epor t ed by two of us (Johannes Geiss

and David C. Hess) has been submit ted to the As t rophys ica l Journal for

publication.

Some further work will be done separa te ly and also in con

nection with the t r i t i u m dating problem.

* F e r m i Institute for Nuclear Science.

^ Now at Phys ika l i sches Inst i tut , Univ. of Bern.

II-29-9 11-34-13

^ ^

II-38-5

38-5 Mass Spec t romet r ic Study of Charged Atomic and Molecular Products of Nuclear Transformat ion (5230)

D. C. Heaa and S. Wexler

Posi t ively charged fragments f rom the dissociat ion of 1, 2 — s ° m

dibromoethane by i somer ic t rans i t ion of 4. 58-hr Br and ^--y decay of

35. 9-hr Brg and f rom the disrupt ion of t r i t i a ted ethane by beta decay of

t r i t i um were observed in the completed mass s p e c t r o m e t e r , MA-23. 8 Cm

The resu l t s in the Br t rans i t ion indicate the p resence of

multiply charged bromine ions as well as an apparent violent disrupt ion of

the dibromoethane molecule. The following ions have been identified thus + 2 J. 3+ 4+ 6+ 8J. +

far: Br , Br , possibly Br , Br , Br , Br , (CgH^Br) , (CH Br) + , + + + ++ + +

posit ive ions in the range f rom (CgH^) to Cg , C , C , Hg and H . The many fragments detected in this decay a r e the r e su l t of the high posi t ive

ao charge which develops in the Br a tom following in te rna l convers ion.

Auger cascades which fill vacancies in the inner e lect ronic shel ls cause

the loss of numerous e lec t rons f rom the molecule. An average cha rge of 1 ao m

+10e has been measured for the dissocia t ion products of Cg H^ Br

Several modes of disrupt ion a r e apparent ly open to the dibromoethane mole

cule .

In con t ras t to the violence done to the molecule in in te rna l 82

convers ion , the effect in beta decay is re la t ive ly mild. When Br incorpora ted 8 2

in 1, 2 -CgH Brg undergoes t r ans fo rmat ion to Kr , the only ionic fragment

observed at low pres-sures was (CgH Br) . Neither the init ial product f rom

the beta t r ans i t i on , (CgH Br -Kr ) , nor Kr were found. As the p r e s s u r e

of radioact ive gas is i n c r e a s e d , the (CgH ) ion a p p e a r s . The ra t io of

intensity of this f ragment to that of (CgH. Br) i n c r e a s e s with the p r e s s u r e . +

The (CgH ) f ragment thus appears to be formed in a col l is ion of the v i -brat ional ly excited (CgH^Br) with a CgH^Brg molecule in the sou rce chamber . Study of the disrupt ion of this molecule is continuing.

1 S. Wexler , Phys . Rev. 9 3 , 182 (1954).

II-38-5 69

The yields of the ionic fragments fro mi the dissociat ion of 2

CgHg T gas following beta decay of t r i t i um a r e p resen ted in Table VIII.

TABLEVin, Fragmenta t ion of CgH^T from p-decay of t r i t i um.

F r a g m e n t

CgH"*"

C g H g +

C a H 3 ^

C a H ^ " "

M a s s 30

M a s s 31

F r a c t i o n a l y i e ld a t s t a t e d t o t a l s o u r c e p r e s s u r e s

; v 5 x l 0 m m

0 . 0 1 5

0.Q36

0 .069

0 . 0 5 6

q.oi

0. 79

O.qu

0 . 0 1 2

_6 ^4. 5 xlO m m

0 . 0 2

0 . 0 4 2

0 . 0 6 3

0 . 0 6 3

0 . 0 0 5

0 . 7 9

a. 02

_6 /j^ 9 X 10 m m

0 . 0 1 6

0 . 0 4 5

0 . 0 7 8

0 . 0 7 4

0 . 0 1

0. 77

0 . 0 2

_ 5 j^2. 4 X 10 m m

0. 016

0 . 0 3 9

0 . 0 6 5

a. 065

0. Oi

0. 77

0 . a 2 4

0 . 0 2 4

The data obtained at s e v e r a l o v e r - a l l p r e s s u r e s of act ive gas

in the sou rce show that l i t t le change in the re la t ive abundances occurs

over an eight-fold var ia t ion of p r e s s u r e . We there fore feel confident that

the ions observed come direct ly f rom the fragmentat ion resul t ing f rom the

beta t rans i t ion and not f rom secondary p r o c e s s e s such as beta ionization

and charge exchange. +

Ions of the type (CH) were found in l ess than 0. 01 yield at the

higher p r e s s u r e s , but these may be due to the p r e sence of a sma l l impur i ty

of t r i t i a ted methane in the sample . Even if these ions a r e indeed the r e su l t

of breakage of the C-C bond in e thane , their low yield suggests that no

violent disrupt ion of the molecule occurs following the beta t rans i t ion .

2

The sample of t r i t i a ted ethane was p repa red for us by K, E . Wilzbach of

the Chemis t ry Division.

70 II-38-5

F u r t h e r , the absence of H , Hg and He in the mass spec t rum demon

s t ra t e s that the charge stays with the heavy fragment. Perhaps the most

s tr iking aspect of the data is the depressed intensity of the (Cg H. ) f rag

ment. This effect may possibly give an insight into the mechanism of the

dissociation process as well as the maximum electronic and vibrational 4- 3 3

energy given to the CpH radica l ion in the beta t ransi t ion of H to He .

16 8TASE ELECTRON MULTIPLIER

TRAP a 4 5 0 f / t i c PUMP

90* SPHERICAL DEFLECTOR

Calculations along this line a re in

p r o g r e s s .

The machine used in

these studies of radioact ive decay

is pictured schematical ly in Fig.13.

It is a 60 magnetic analyzer of

12 in. radius and uses a 16-stage

s i lve r -magnes ium electron mult i

plier to detect the ions.

To avoid an inc rease

in background at the multiplier

because of s t reaming of uncharged,

undecayed par t i c les (atoms or mole

cules depending on the exper iment ) , the sys t em has multiple differential

pumping. The detector end has two 20 i / sec glass mercury pumps , one

of which pumps the detector region direct ly while the other pumps on

the analyzer tube. These two regions a re connected essent ial ly only

by the slit through which the ions p a s s . One metal mercury pump having

a ra ted speed of 450 f/sec is connected to the region immediately before

the magnet. This region is coupled to the tube by an aper ture which

must be l a rge r than that at the collector because of divergence of the beam.

A fourth pump with a speed of 450 i / s e c , evacuates another chamber

which contains a 90 spher ica l -sec tor e lectr ic deflector of 3 in. mean

rad ius . The entrance of the e lec t r ic deflector faces the outlet of the ion

chamber . Since the exit aper tu re of this chamber is a hole of 11/16 in.

Fig. 13. Mass spec t rometer for radioactive gases .

II-38-5 71

d iame te r , t he re is a considerable am.ount of un-ionized gas escaping. B e

cause of the conical shape of the ion c h a m b e r , this gas forms a crude un

charged beam which is sca t te red by the spher ica l deflector plate . The beam

is thus converted to a random gas and the pump mentioned before is able to

ext rac t most of it. Without the def lector , most of the nevitral beam would

s t r ike the analyzer tube at the bend in the magnet and much of it would find

its way up to the detector . The detector would then operate in a l a rge r pa r t i a l

p r e s s u r e of radioact ive gas and the background would be higher . Even with

this a r r a n g e m e n t , shielding of the detector is s t i l l n e c e s s a r y to reduce the

background produced by radia t ion from act ive m a t e r i a l which col lec ts in the

t r a p s .

The ion source used with the spher ica l deflector is a s ta in-o

l ess s teel cone with a half angle of 5 and a length of 80 in. Ins ide , mounted

on feed-through i n s u l a t o r s , a r e 39 r ings which approximately define the source

region. A spher ica l ly symmet r i ca l potential dis t r ibut ion (with the cen te r of

the sphere corresponding to the apex of the cone) is obtained by applying

appropr ia te voltages to the r ings . This gives a guide field whose l ines of

force a r e essent ia l ly r a d i a l , d i rec ted toward the (projected) apex of the cone.

There will thus be an ion beam converging to a point and then diverging.

This diverging beam is crudely refocussed at the source sli t region by the o

spher ica l - l ens effect of the 90 deflector . We have then a diverging beam of o o

half angle 5 . The spec t romete r accepts a half angle of about 3 1/2 so al l

of the available solid angle of the spec t romete r is filled.

P r e l i m i n a r y exper iments were c a r r i e d out to m e a s u r e the 4 1

charge s ta tes of po tass ium daughter ions from p"-decay of 1. 8-hr A ++

Singly charged K ions were observed in approximate ly 95% of the decays , K 34.

in about 5% and K in about 0. 5%. These studies were conducted in the 1. 2 i cone descr ibed in the previous s u m m a r y r epo r t .

40-2 Fragmenta t ion of Methane and Methyl Bromide (5230)

James Morr i son * and Henry E. Stanton Reported by Henry E. Stanton

Studies of the b r eak -up under e lec t ron impact were c a r r i e d on in

continuation of the work previously r e p o r t e d , and the r e su l t s have a b e a r

ing on the heat of vaporizat ion of carbon. This quantity has been in dispute

for s e v e r a l y e a r s , the a rgument being cen te red about two va lue s , 55 120 kca l /mo le

and ^ 170 k c a l / m o l e . The findings he re support the higher value.

It has been repor t ed by McDowell and War ren that C ions c r ea t ed

f rom methane under e lec t ron impact a r e formied without kinetic energy. On

the bas i s of this and measu remen t s of appearance po ten t ia l s , they bel ieve

the fundamental p r o c e s s to be

CH^ + e —• C"*" + 4H + 2e. (1)

This leads to the lower value for the heat of subl imat ion of carbon. 2

As repor t ed las t t i m e , the kinetic energy of the fragment ions was

measu red in MA-17, and it was found that the C ions had an init ial energy

of ' ^O . 1 ev. Somewhat more must be c a r r i e d away by the hydrogen a toms or

molecules formed in the b reak -up .

If this additional energy is included in Eq. (1), the energy balance

does not conform to known values of the var ious bond ene rg i e s . Accordingly,

the p r o c e s s which bes t s e e m s to fit the exper imenta l findings is

CH^ + e —>• C"*" + Hg + 2H + 2e + K. E. (2)

1 C. A. McDowell and J. W. W a r r e n , Disc, Fa raday Soc. 10, 53 (1951).

2 Physics Division Summary Repor t , ANL-5698, F ig . 19.

II-40-2 73

Assuming this re la t ion , and using the definit ions,

+ +

A(X ) = the appearance potential to form X ,

I (Y ) = ionization potential of the gas a tom Y,

D(U-V) = the bond energy of the atoms U and V in a molecule , the energy eqviation is

A(C"'') = 1(0""') + 4D(C-H) - D(H-H) + K. E. (3)

4-F r o m measu remen t s to be descr ibed l a t e r , A(C ) was found to be 26. 7 ev

and the K. E. t e r m '^ 3 ev , which is cons is tent with the d i rec t m e a s u r e m e n t s .

It is known that D(H-H) = 4. 48 ev and I(C ) = 11. 27 ev. One then finds

4(D-H) = 16.91 ev.

The heat of formation of methane with all e lements in thei r s t and

a r d s ta tes is known to be 0. 74 ev.

Hence if the heat r e l e a s e d in the reac t ion is designated by AH, one

can compare the equation,

C(g) + 4H—KCH^ AH = -16 .91 ev = 396 k c a l / m o l e , (4)

found in these exper iments with the equat ion,

C(s) + 2H2-»'CH^ A H ' = -0 . 74 ev = 17. 3 k c a l / m o l e , (5)

for the e lements in thei r s tandard s ta tes to get the equation,

C ( g ) - ^ C ( s ) AH ^, = + 7.21 ev = + 166 k c a l / m o l e . (6) subl

This heat of subl imation AH , , ag ree s with the "high value" well within subl

exper imenta l e r r o r s .

The appearance potential 'A(C ) was de te rmined in MA-17 as a

check with the values in the l i t e r a t u r e to make s u r e that the s a m e p r o c e s s e s

were involved. A typical t r a c e is shown in F ig . 14 where a s i m i l a r cu rve

for Ne has been super imposed for ca l ibra t ion and compar i son . One notes

that the approach to the axis for low e lec t ron energ ies is much more gradual

for C than Ne . This indicates that the C is formed with ini t ia l kinetic

74

"7

22 24 26 28 IONIZING ELECTRON VOLTAGE

Fig. 14. Typical curve of ionization efficiency for the formation of C^and Ne'''by e lect ron impact. For compar i son , the two curves a re shown on the same set of axes.

II-40-2

energy , as found also by the energy

analys is .

The possible existence

of initial kinetic energy in the

formation of C is m^ore c lear ly

evident in Fig. 15 where the

second derivat ives of the curves

shown in Fig. 14 are plotted as

a function of e lect ron energy.

The relat ively na r row peak of +

Ne in Fig. 15 is cha rac te r i s t i c

of the formation of ions initially

at r e s t , the width being due to

the distr ibution of energies in the

ionizing e lec t rons . For C ,

however , the inc reased width of

the second derivat ive curve indi

cates that the total kinetic energy

24 26

ENERGY ( e v )

26 30

Fig. 15. Curves showing the second derivative of the ion intensity with respect to the ionizing e lect ron voltage. The re la t ively nar row peak of Ne indicates formation with the atom at r e s t , whereas the wide peak of C"'' indicates init ial kinetic energy.

II-40-2 75

in the reac t ion is approximately equal to the half width. In both c a s e s , the

maxima of the curves give the appearance potentials of the i ons , which a r e

c lose to the general ly accepted va lues .

This ma te r i a l is in p repara t ion for publication in the Journal

of Chemical Phys ics .

-7^ V-2-15

V-3-5

V. THEORETICAL PHYSICS, GENERAL

2-15 Excited States of Light Nuclei . (5220)

Dieter Kurath

There has been some in te res t in measur ing the l ifet ime 6

of the 3. 57-Mev second excited s tate of Li because it is easy to produce .

A calculat ion of the lifetime of this Ml t rans i t ion from a s ta te virith

J = 0, T = 1 to the ground s ta te (J = 1, T = 0) shows that it is ve ry shor t .

The computed value is re la t ive ly insensi t ive t6 the spi t i -orbi t coupling

p a r a m e t e r and is _ 1 7

T ^ 7. 5 X 10 s ec .

This r epo r t t e rmina t e s the study of excited s ta tes of light

nuclei . The r e su l t s a r e contained in a paper ent i t led, "Radiative T r a n s i

tion Widths in the I p - S h e l l " , Phys . Rev. 106, 975 (1957).

3-5 Dynamics of Nuclear Collective Motion (5220)

David R. Inglis and Kiuck Lee Reported by David R. Inglis

The possibi l i ty of s table pea r - shaped deformations of nuclei

is t r ea t ed by a per tu rba t ion theory s ta r t ing f rom the nucleon wave functions

of a spheroidal ha rmonic -osc i l l a to r potent ia l , without sp in-orb i t coupling.

The mixing of s ta tes of opposite par i ty tends to stabilize, the deformation

and is opposed by the cohes iveness of nuclear mat ter that favors a s p h e r i

cal shape. The former is calculated explicitly for a number of cases and

the la t te r is es t imated by imposing a constant -volume condition in a s imple

77

manner closely analogous to a more famil iar treatm.ent of spheroidal defor

mations. In this approximation the mixing of the s ta tes is not quite enough

to overcome the competing effect, so it mere ly "sof tens" the nucleus and

does not s tabi l ize a pea r - shaped deformation. The difference between the

competing effects va r i e s between about th ree and twenty percent in var ious

favorable cases considered. Spin-orbit coupling br ings s ta tes of opposite

par i ty c loser toge ther , as is famil iar in the formation of the "magic num

b e r " groups , and it is expected that its p r i m a r y effect i s , through the energy

denomina to rs , to i nc rease the tendency to pea r - shaped nuclei enough to

make some of them s table . A r e p o r t on this work has been submit ted for

publication.

Because this t r ea tmen t suggests a mechanism whereby the

f i ss ion-saddle may be a s y m m e t r i c , it is of in te res t to examine other a t tempt

to explain fission a s y m m e t r y , pa r t i cu la r ly the behavior of the droplet model.

The deformed shape is so far from spher ica l that it is awkward to use an

expansion in spher ica l h a r m o n i c s , and an approximate t r e a tmen t in t e r m s

of sma l l deviations fro mi a cylinder capped by hemisphe res is ins t ruc t ive .

Such a cylinder itself becomes unstable to fission only for a surface tension

about half as s t rong as the empi r ica l value. A neck s t a r t s to form more

eas i ly , but st i l l r equ i res r a the r weak surface tension. It s t a r t s to form

considerably more easi ly in the symmet r i c position; but i f , neve r the l e s s ,

it is s t a r t ed a symmet r i ca l ly an es t imate based on the hydrodynam.ics in

dicates that it develops at f i r s t slightly more rapidly in a way that may be

assoc ia ted with a reduced m a s s .

No further r epor t s on this t i t le a r e expected for the next year

because of absence of the au thors .

^%

V-5-3 V-9- l

5-3 In termedia te Surface Coupling in Even-Even Nuclei (5220)

B. James Raz

In order to invest igate the t rans i t ion region between weak

and s t rong coupling in the Bohr-Mot te lson collective model , a s e r i e s of

calculat ions using in te rmedia te surface coupling have been init iated. This

study is a imed at explaining the observed deviations from pure rota t ional

spec t r a by examining the var ia t ion of theore t ica l ly predic ted spec t r a of

even-even nuclei with changes in a) the two-par t ic le in terac t ion and

b) the s t rength of surface coupling. Specifically, the spec t r a of two

equivalent pa r t i c les with j = 7/2 a r e being ca lcu la ted , taking account of 43

the two-par t ic le in terac t ion found suitable for Ca and including varying

s t rengths of surface in teract ion.

During the repor t ing pe r iod , the energy levels and the

assoc ia ted eigenfunctions for 1 = 0, 2 , 4 and 6, and the values of B(E2)

for 1 = 0 and 1 = 2 have been computed for a fixed two-body in terac t ion

and var ied amounts of surface coupling.

At p re sen t the ca lcu la t ions , in which the s t rength of the

two-body in terac t ion is v a r i e d , a r e being run on the AVIDAC.

The r e su l t s indicate that the observed level spacing can

be obtained for reasonable choices of the p a r a m e t e r s and that the observed

var ia t ion of B(E2) with energy can also be obtained with these p a r a m e t e r s .

A full r epo r t of this project is now being p r e p a r e d for

publication.

9-1 Collect ive Effects of O (5220)

B. James Raz

Upon the appearance of a new measuremient of the quadrupole

79

17

m o m e n t of O t h e fo l lowing p a p e r w a s w r i t t e n a s a L e t t e r to t h e E d i t o r

of the P h y s i c a l Rev i ew and wi l l a p p e a r in t h e Augus t 15 i s s u e . 17

The v e r y s h o r t l i f e t i m e of t h e f i r s t e x c i t e d s t a t e of O at 1

0. 872 Mev c a n be a c c o u n t e d for e a s i l y by t h e i n t r o d u c t i o n of s m a l l 2

c o l l e c t i v e e f f ec t s . If t he a s s u m p t i o n i s miade t h a t the p a r a m e t e r s of the

t h e o r y a r e the s a m e for a l l l e v e l s of a g i v e n n u c l e u s , t h e l i f e t i m e of t h e

f i r s t e x c i t e d s t a t e d e t e r m i n e s t h e o r e t i c a l l y the q u a d r u p o l e m o m e n t of

the g r o u n d s t a t e . Th i s p r e d i c t i o n of t h e va lue of the q u a d r u p o l e m o m e n t 3

w a s m u c h l a r g e r t h a n the e x p e r i m e n t a l l y m e a s u r e d v a l u e of Q = - 0 . 005 - 2 4 2 4

X 10 c m . R e c e n t l y t h i s quan t i ty has b e e n r e m e a s u r e d and t h e n e w

e x p e r i m e n t a l va lue i s in e x c e l l e n t a g r e e m e n t w i th t h e p r e d i c t i o n b a s e d on

t h e l i f e t i m e of t h e f i r s t e x c i t e d s t a t e . - 1 0 T = 2. 5 ± I X 10 s e c ( r e f e r e n c e 1) (1)

Q ( theory) = - 0 . 030 ±0. 006 X 10" c m (2) _ 2 4 2

Q ( e x p e r i m e n t ) .= - 0 . 026 ±0. 009 x 10 c m ( r e f e r e n c e 4) (3)

T h i s r e l a t i o n s h i p i s c a l c u l a t e d by u s i n g p e r t u r b a t i o n t h e o r y , s i n c e the a

c o l l e c t i v e ef fects a r e s m a l l . If the a s s u m p t i o n i s m a d e t h a t (hoj) i s m u c h

g r e a t e r t h a n 1 M e v , t h e n on ly one p a r a m e t e r r e m a i n s i n t h e s o l u t i o n s . T h i s

p a r a m e t e r is <^ |k(r))^ / C , w h e r e k ( r ) i s the r a d i a l funct ion t h a t d e t e r m i n e s

1 J. T h i r i o n and V. L . T e l e g d i , P h y s . Rev . 9 2 , 1253 (1953).

2

A. B o h r and B . R. M o t t e l s o n , K. D a n s k e V i d e n s k . Se l sk . Mat . - f y s . Medd. £ 7 , No. 16 (1953); J. P . E l l i o t t and B . H. F l o w e r s , P r o c . Roy. Soc . A 2 2 9 , 526 (1955); F . C. B a r k e r , P h i l . Mag . S e r . 8 , I , 329 (1956); s e e a l s o B . J . R a z , t h e s i s . U n i v e r s i t y of R o c h e s t e r , 1955 ( u n p u b l i s h e d ) . 3

G e s c h w i n d , G u n t h e r - M o h r , and S i l v e y , P h y s . Rev . 8 5 , 474 (1952). 4

M. J. S t e v e n s o n , B u l l . A m . P h y s . Soc . 2 , 31 (1957) and p r i v a t e c o m m u n i c a t i o n , and P h y s i c a l R e v i e w (to be p u b l i s h e d ) .

V-9-1 V-15-5

5

the effective coupling and C is the surface deformation p a r a m e t e r . The

value of ^ | k ( r ) ) / / C , which is de termined from Eq. (I) and used in 1 / 3 . 1 3

Eq. (2) , is 0. 21 ± 0. 04 if R^ is taken as 1. 41A x 10 cm. 17

Thus , on O the s t ra ight forward application of the co l l ec

tive model with weak coupling gives consis tent r e s u l t s .

5 See Bohr and Mottelson, r e fe rence 2.

15-5 Energy-Leve l Density of a System of F e r m i Pa r t i c l e s (5220)

Norber t Rosenzweig

The following is the abs t r ac t of a paper which has been

submit ted to The Physical Review for publication.

Some fea tures of the influence of shel l s t r uc tu r e on the level

density of a highly excited nucleus (^10 Mev) a r e studied on the bas i s of

an idealized independent-par t ic le model for which accura te formulas can

be obtained in closed form. The theory is especia l ly useful for e s t i

mating the ra t io of the level densi t ies of two nuclei in which the s ame de

generate (shell model) levels a r e being filled in the ground s t a t e , but which

differ by one or two units in the number of pa r t i c l e s which occupy these

l eve l s . Observable effects p e r s i s t to high energ ies (?i/lO Mev) and they

become ve ry l a rge in the neighborhood of the magic n u m b e r s . T h u s , it

may be possible to de te rmine exper imenta l ly whether or not the shel l model

of the nucleus re ta ins any validity at high exci ta t ions.

V-16-1 81

16-1 Analysis of Angular Distr ibution Data (5220)

J. E . Monahan and Gilbert Steiner

I. CENTER-OF-MASS TRANSFORMATION MATRICES FOR THE COEFFICIENTS OF THE EXPANSION IN LEGENDRE POLYNOMIALS

Reported by J. E. Monahan and Gilbert Steiner

Consider the reac t ion

m^ + rc^ + Q ' = mg + m^ ,

I

where Q is the negative of the usual Q-value of the r eac t ion , m and m

a r e the masses of the incident and observed pa r t i c l e s and nrig and m a r e

the masse s of the t a rge t and res idua l nuc le i , respec t ive ly . The differen

t ia l c r o s s sect ion for this p roces s can be expanded in the fo rm

.L(JX^) = ( . / 4 . ) £ - P ( ^ ^ ) , i=o

where c o s " |i ^ is the angle of sca t t e r ing obse rved in the l abora tory ; or

CX3

<r ( . ) = ((r/4.) 2 2 7 i<^ c) i =o

where cos" [i is the corresponding angle in the c e n t e r - o f - m a s s sys t em:

n 2 . 1 / ^ , , 2 1/2

where

^ c - ^ ^ L

2 "^l"^3("^3 + " \ ) ^r

E is the initial energy of re la t ive motion in the c e n t e r - o f - m a s s sy s t em.

82

The re la t ions between the coefficients w and Tf a r e

and

where

2 i ' + l ^

V-16-l

and

"-IV- - T - / ^ ' ' > ' L ^ i ' ' ' c ' P < . ' ' ' L ' '

-1 2 i ' + 1 /•! t = ., I d u P (UL, ) P (u ) .

The evaluation of these i n t e g r a l s , c o r r e c t to t e r m s of order y > gives

^ fi 2 . - i ' ( i ' + l)(2i'^+ 2i' - 3 ) ) , i ' , iV{V -I) , i ' - i i i - - r - ^ ; - 2(2i ' . l ) (2i '+3) ; ^ + ^ t 2 i ' - l \

(i'+l)(i'-!-2)'. . i ' + l ] , 2 r ( i ' + l ) ( i ' + 2 ) ( i ' + 3)^ i ' + 2 2i« + 3 : '*i J "^^ \ 2(2i> + 3 ) ( 2 i ' + 5 ) ^i

+ i ' ( i ' - l ) ( i ' - 2 ) ^ ^ i ' - 2 ] 2 ( 2 i ' - l ) ( 2 i - - 3 ) ^ i J '

and

, -1 _ / , 2 i ' ( i ' + l ) ( 2 i ' ^ + 2 i ' - l ) , i ' . r( i '+l)(iH-2) , i '+ 1 ^ i i ' M ^ ' ^ 2(2i-- l)(2i '+3) l ^ i •*"^1 2i '+3 *i

- 2 , 7 1 •• 6 / f + \ / i ' ( i ' - I) ( i ' -2 ) , i ' - 2 . ( iM-l)^( i '+2)( i '+3) i ' • ^ ' C 2 ( 2 i ' - l ) ( 2 i ' -3) ^i " 2 (2 i ' + 3)(2i ' +5) ' i

+ 2

v-16-1 83

3

F o r sca t t e r ing , y reduces to m^ /m^g s ° that y is l e ss than

0. 001 even for sca t te r ing f rom an element as light as carbon. Thus if an ex

pansion

I =o

with N finite, can be justified for a differential sca t t e r ing c r o s s sec t ion ,

then the corresponding expansion,

N+i orj^(fxJ=(./4.) I ; O . ^ P ( ^ L ) , (1)

i=o

3

is accura te to t e r m s of o rder -y .

II. STATISTICAL ANALYSIS

Reported by J. E. Monahan

In o rder for Eq. (1) to be an accura te r ep resen ta t ion of the

differential c r o s s sect ion cr (|JL ) for values of |j. o ther than those at which

data a r e taken, it is n e c e s s a r y that N be sufficiently l a rge that co is e s s e n -i

t ial ly zero for i > N + 1. The purpose of this note is to desc r ibe a c r i t e r i o n

for the sufficiency of the r ep resen ta t ion (1) for a given finite value of N.

Let C(fjL.) denote the number of s ca t t e r ed pa r t i c l e s measured

by the detector placed at the angle c o s " |j,. ; and let (T. denote the average J J i

value of P.(fJ.) for this de tec tor . Then N+i

where A is a constant independent of j and i . If A. denotes the e r r o r (stand-

ard deviation) in the determinat ion of C(jj,.), the "most p robable" set of

v-16-1

?i| coefficients compr i se s those values A oj which minimize the quadrat ic

express ion

N+i 2 s r N+i -, X = JZ^r^U ZZ^ - -c( . )(

j = i J 1- i^o j i i •' \

(3)

where s ^ N + 2 is the nuinber of distinct angles at which C(|Ji.) is de t e r -

mined.

It is obvious that OC is a measure of the "goodness of the

fit" of the expansion (2) to the exper imental ly de te rmined C( jji . ) . If the fit

is too good re la t ive to the expected uncer ta in t ies A. , one might suspect that

t e r m s which a re s ta t i s t ica l ly non-significant a r e included in the expansion

(2) for the value of N chosen. In this ca se "^^^ would be a very sma l l num

ber . On the other hand, ve ry la rge values of A, would r e su l t for values of

N such that significantly non-ze ro t e r m s a r e excluded from Eq. (2). Thus

for the " c o r r e c t " value of N, ')C should be nei ther "too l a r g e " or "too

smal l . " It might be noted that the " c o r r e c t " value of N depends on the e r r o r s

A. , i. e. , a value of N is " c o r r e c t " if it excludes only those coefficients

which a r e ze ro within the s t a t i s t i ca l accuracy of the exper iment .

In o rder for these qualitative notions to be of any p rac t i ca l

va lue , it is n e c e s s a r y to obtain the s ta t i s t i ca l dis t r ibut ion of "^ • If it is

a s sumed that the e r r o r s A. a r e normal ly d is t r ibu ted , it can be shown that J

the quantity defined by Eq. (3) has a ch i - squa red dis t r ibut ion with (s - N - 2)

degrees of f reedom, its expectation value and var iance being given by

<X=> . = s - N - 2 , Av

and

<r>Av - xr> Av = ^ ( - N - 2 ) .

v-16-1 V-17-4 ^5

V-18-1

The s ta t i s t ica l significance of the fit for a given value of N is obtained from

the probabil i ty P(% yX ) of obtaining a value of A grea te r than the value 2 '•

9C calculated using Eq. (3). Tables of this probabil i ty a r e included in

most texts on Ivlathematical Sta t i s t ics .

Since the dis t r ibut ion of % does not depend on any p rop

er t ies of the Legendre polynomials , this tes t can be general ized to any r e

presenta t ion in which an exper imental ly de te rmined quantity is expanded in

a s e r i e s of known functions of an exper imenta l var iab le .

17-4 Analysis of Angular Distr ibutions and Corre la t ions (5220)

William C. Davidon

A paper descr ibing the p rocedure for numer ica l ly locating

the minimum of a function of s eve ra l var iab les was submit ted for publica

tion in the Journal of Mathematics and Phys ics .

18-1 P a r a m e t r i c Formula t ion of Quantum Mechanics (5220)

William C. Davidon

In o rde r to obtain a more sa t i s fac tory re la t iv i s t i c theory of

s ca t t e r ing , par t icu la r ly when la rge in teract ions a re involved, an effort is

being made to const ruct a more complete theory based on a p a r a m e t r i c for

mulation of quantum e lec t rodynamics . ^

When la rge interact ions a r e involved, the development of the

W. C. Davidon, Phys . Rev. 97, 1131, 1955; Phys . Rev. 97 , 1139, 1955.

v-18-1 V-19-4

V-40-4 ^ 4 V-42-4

S mat r ix by a per turbat ion s e r i e s expansion in powers of the coupling con

stant is not sa t is factory . It is n e c e s s a r y to find a definition and means of

evaluation of the S mat r ix in the p a r a m e t r i c formulation which, unlike the

one used e a r l i e r , does not a s sume the convergence of the per turba t ion ex

pansion. It is also n e c e s s a r y to general ize to couplings other than the

e lec t romagnet ic field.

19-4 Ingoing-Wave Condition in Scat ter ing Theory (5220)

Melvin Hack

A rev i sed ve r s ion of a paper on this work has been c o m

pleted and has been submitted for publication.

40-4 Quantum Mechanical Ergodic T h e o r e m (5230)

Hans Eks te in

This paper will appear in the July 15 i s sue of the Phys ica l

Review. There will be no further r e p o r t s on this project .

42-4 I r r e v e r s i b l e P r o c e s s e s in Quantum Mechanics (5230)

Hans Ekste in and N. Rostoker (General Dynamics , San Diego) Reported by Hans Eks te in

The paper has been submit ted for publ icat ion, after some

modification by the co-au thor .

V-43-2 V-44-8

V-45-8

43-2 Fie ld Theory of Nonrelat ivis t ic Moving Nucleons (5230)

Hans Ekstein and D. Kaplan

Calculations of mat r ix e lements by per turba t ion calculus

have been c a r r i e d out and a r e being checked. Calculations have been

c a r r i e d , thus fa r , to the 4th order of the r enorma l i zed coupling constant.

* Illinois Institute of Technology.

44-8 Fixed-Source Meson Theory (5230)

H. Eks te in , J. C. Swihart and K. Tanaka Reported by K. Tanaka

A paper entit led "Representa t ion less Formula t ion of F ixed-

Pa r t i c l e Fie ld Theo r i e s " was presen ted by H. Ekste in at the Seventh

Annual Rochester Conference in Apr i l , 1957.

A paper entit led " P r o p e r t i e s of the Fixed-Source Meson

Theory" by K. Tanaka is scheduled for publication in the July 15, 1957

i ssue of the Physical Review.

45-8 Meson-Nucleon Interact ion (5230)

Katsumi Tanaka

1 Salzman's per turba t ion r e su l t in Chew's no - reco i l theory

1

G. Salz man, Phys . Rev. 99, 973 (1955).

v - 4 5 - 8 V-48-3

for neu t ron-e lec t ron in te rac t ion , in which one calcula tes the in terac t ion of

the e lec t ros ta t ic field of the e lec t ron with the charged meson cloud of the

physical neu t ron , is in se r ious d i sagreement with exper iment . T r e i m a n and

Sachs found that the higher o rder mesonic cor rec t ions in the f ramework of

the Chew theory reduce the d iscrepancy by about 20%.

In o rder to examine the nucleon effects on the d i sc repancy ,

we have per formed a covar iant calculat ion of the meson -cu r r en t par t of the

neu t ron-e lec t ron in te rac t ion , using d i spers ion re la t ions der ived by Chew

et al . , under the assumpt ion that the (3,3) resonance dominates the d i spe r

sion in tegra l . Such a covar iant calculat ion has many advantages over the

previous non-convar iant ca lcula t ions . It is found that the d i sc repancy is r e

duced considerably .

S. B. T r e i m a n and R. G. Sachs , Phys . Rev. 103, 435 (1956).

48-3 Dispers ion Relations (5210)

William C. Davidon

At the Roches ter Conference on High Energy P h y s i c s , Puppi

r epo r t ed on an apparent d i sc repancy between ir" - p r o t o n sca t t e r ing exper iments

at low energ ies and the cor responding d i spers ion re la t ions for non-spin-f l ip

forward sca t te r ing . An independent examination of the possibi l i ty of such a

d i sc repancy was made he r e . At low e n e r g i e s , the d i spers ion re la t ions b e

come an identity since the sca t t e r ing lengths appear explicit ly in them. A

numer i ca l calculat ion was miade at 65 Mev, at which energy the d i spe r s ion r e

lations a r e no longer t r i v i a l . Agreement within the es t imated exper imenta l

V-48-3 V-50-1 89

uncer ta int ies was obtained. These resu l t s were communicated to Puppi ,

Goldberger , and Oehme, and further work will be done on this nnatter when

more detailed information is rece ived from Puppi on his ca lcula t ions .

50-1 Neutrino Theory (5220) *

M. Goeppert Mayer and Valentine L. Telegdi Reported by M. Goeppert Mayer

To overcome ce r ta in d i sc repanc ies between exper iment and

the predict ions of conventional 2-component neutr ino theory , a "twin neu

t r ino" theory is proposed. In the more genera l formulation of this t heo ry ,

two different 2-component neutr inos v, , v^ of opposite s c r e w - s e n s e a r e

in t roduced, together with the i r ant ipar t ic les T ^ ^ • Ii be ta decay , one of

these is coupled by T , V , the other by S^A. This e l iminates all in te r fe rence

te r ms .

The theory is special ized to the assumpt ion T, = v^ , i. e. ,

to Majorana-type neut r inos . This more r e s t r i c t e d theory is equally s u c c e s s

ful in explaining the r e su l t s of the "par i ty expe r imen t s " . It is shown that

the conventional objections to the Majorana theory need not apply to this

twin neutr ino theory.

A paper on the subject , enti t led " 'Twin Neut r inos ' : A Modi

fied 2-Connponent Theo ry" , will appear in the Physica l Review on September 1.

* Univers i ty of Chicago.

t )^/i/,^sl

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