ANL-6574 Physics AEC Resea rch and Development Report

ARGONNE NATIONAL LABORATORY 9700 South Cass Avenue

Argonne^ Illinois

PHYSICS DIVISION SUMMARY REPORT

June 1962

Morton Hamermesh^ Division Director

Preceding Summary Repor t s :

ANL-6488, January 1962 ANL-6517, F e b r u a r y - M a r c h 1962 ANL-6534, Apr i l -May 1962

Operated by The Univers i ty of Chicago

under

Contract W-3i - 109-eng-38

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.

FOREWORD

The S u m m a r y Repor t of the Phys ics Division of the

Argonne National Labora to ry is i s sued monthly for the information

of the m e m b e r s of the Division and a l imited number of other pe rsons

in te res ted in the p r o g r e s s of the work . Each active project r epor t s

about once in 3 months^ on the ave rage . Those not r epor ted in a

pa r t i cu la r i s sue a r e l isted separa te ly in the Table of Contents with

a re fe rence to the las t i s sue in which each appeared .

This is m e r e l y an informal p r o g r e s s r e p o r t . The

r e su l t s and data there fore miust be understood to be prelimiinary and

tenta t ive .

The i s suance of these r epor t s is not intended to con­

stitute publication in any sense of the word . Final r e su l t s either

will be submitted for publication in regular professional journals

or_, in specia l c a s e s , will be p resen ted in ANL Topical Repo r t s .

TABLE OF CONTENTS

The date of the las t preceding repor t is indicated after the t i t le of each project below. Pro jec t s that a r e not repor ted in this i ssue a r e l isted on subsequent pages .

EXPERIMENTAL NUCLEAR PHYSICS

1-22-18 SCATTERING OF CHARGED PARTICLES (ANL-6534, Apr i l -May 1962)

H, W. Broek and J. L, Yntema . . . .

Groups of alpha par t ic les whose angular dis t r ibut ions correspond to i = 2 a r e seen at excitations of about i MeV in all t a rge t s studied. These t a rge t s a lso yield groups of i = 3 alphas at about 4 MeV excitation. These groups a r e usually excited more strongly in even-even t a rge t s than in odd-A t a r g e t s . For the t a rge t s studied^ the 3 c ros s section i n c r e a s e s with A, while the 2 c ros s section shows no regular var iat ion with A.

1-31-1 ELASTIC SCATTERING OF PROTONS (New project)

L. L, Lee^ J r . and J. P . Schiffer . , .

P r e l i m i n a r y r e su l t s have been obtained on the e las t ic scat ter ing of 8-MeV protons from Ca40^ Ni58^ Niso , Cu63, and Cu^s using the tandem Van de Graaff genera to r .

1-98-30 UNBOUND NUCLEAR LEVELS IN THE KEV REGION CANL-6534, Apr i l -May 1962)

C. T, Hibdon . . . . . . . . . . . . . .

Revised values of the widths of some of the unbound levels of F^o a r e given. Many peaks were observed in the 130-300 keV region but an analysis of these peaks is deferred until ine las t ic scat ter ing can be taken into account.

PAGE

IV, PLASMA PHYSICS

IV-10-4 MORPHOLOGY OF HIGH-FREQUENCY PLASMOIDS (ANL-6455, November-December 1961)

A. J . Hatch . . . . . . . . . . . . . .

A photographic and visual study of the s t ruc ture of high-frequency plasmoids as re la ted to plasmoid mechan i sms is desc r ibed .

V. THEORETICAL PHYSICS, GENERAL

V-12-1 SENIORITY MIXING IN If. NUCLEI (New project)

R. D, Law son and B . Zeidmaxi . . . .

Trans i t ion s t rengths of neutron pickup react ions a r e calculated for If-^/g nucle i .

PUBLICATIONS . . . . . . . . . . . . . . . . . . . . . . . . .

PERSONNEL CHANGES IN THE ANL PHYSICS DIVISION . . .

PROJECTS NOT REPORTED IN THIS ISSUE

A re fe rence to the las t preceding repor t is given in entheses for each projec t .

EXPERIMENTAL NUCLEAR PHYSICS

1-2. Neutron Detec tors (ANL-6534, Apri l -May 1962), S. I. Bake r , L . M. Bol l inger , and G. E . Thomas .

1-3. Cross-Sec t ion Measurements with the F a s t Neutron Velocity Selector (ANL-6534, Apr i l -May 1962), L. M. Bol l inger , L . M. Bogan, R. T . Carpen te r , R. E . Co te ' , H. E . Jackson , J . P . Mar ion , and G. E . Thomas .

1-7. Gamma-Ray Spectra from Capture in Neutron Resonances (ANL-6i46 , Apr i l -May i960), L. M. Bol l inger , R. T. Ca rpen te r , and H. E . Jackson.

I -10 . Tandem Van de Graaff Acce le ra tor (ANL-6262 5 December 1960), Fo P . Mooring and J. R. Wallace.

I - i l . Instal lat ion and Operation of the Van de Graaff Genera tor (ANL-6488, January 1962), J . R. Wal lace .

1-14. Pulsed Beams for the Van de Graaff Machine (ANL-6391, July-August 1961), R. E , Holland and F . J . Lynch.

1-18. Neutron Polar iza t ion and Differential Cross Sections (ANL-6517, F e b r u a r y - M a r c h 1962), R. O. Lane and W. F . Mi l l e r .

1-19. Nuclear Resonance Absorption of Gainma Rays (ANL-6534, Apr i l -May 1962), S. S. Hanna, G. J , Pe r low, J . P . Schiffer, and J . A, Weinman.

1-28. Angular Corre la t ions in Charged-Par t i c l e Reactions {ANL-6358, Apr i l -May 1961), T. H. Bra id .

1-30. Calculation of Reduced Widths from. Resonant Scattering of P ro tons by a Diffuse Potential (ANL-6534, Apri l -May 1962), J . P„ Schiffer,

1-34, Decay of ^^Er^^a (ANL-6432, September-October 1961), •' S o

S. B . Bur son and R. G. He lmer .

1-35. Decay of ^ ^ L a - s s (19.5 hr) (ANL-6391, July-August 1961), S. B . Burson and H. A. Grench ,

1-55. Capture Gamma-Ray Spectra for Neutrons with Energ ies from 0.1 to 10 eV (ANL-6052, September 1959), S. Raboy and C. C. T r a i l .

1-60. 7. 7-Meter Ben t -Crys ta l Spec t rometer (ANL-6517j F e b r u a r y - M a r c h 1962), R. K. Smi ther .

1-80, Molecular Beam Studies (ANL-6517, F e b r u a r y - M a r c h 1962), W. J , Chi lds , J . Dalman, D. von Ehrens t e in , and L. S, Goodman.

1-102. Neutron Cross Sections by Self-Detection (ANL-6376, June 1961), J . E . Monahan and F . P . Mooring.

I - l l l . Semiconductor Detec tors (ANL-6455, November -December 1961), H M. Mann and J „ W. Hasle t t ,

1-144, Investigation of Scintillator s (ANL-65179 F e b r u a r y -March 1962), L . J . Basi le and W. L. Buck.

MASS SPECTROSCOPY

11-23. Sputtering Exper iments in the Rutherford Collision Region (ANL-6488, January 1962), M. S. Kaminsky.

H-28 . Kinetics of Chemical Reactions in the Gas Phase (ANL-6517, F e b r u a r y - M a r c h 1962), J , Berkowitz and S. Wexler .

11-29. Gaseous Species in Equi l ibr ium at High T e m p e r a t u r e s (ANL-6455, November -December 1961), J . Berkowitz .

11-39. Fragmenta t ion of Cyanogen (ANL-6488 , January 1962), H. E . Stanton.

11-40. Fragmenta t ion of Hydrocarbons (ANL-6534, Apr i l -May 1962), H. E . Stanton.

11-41. Consecutive Ion-Molecule Reactions (ANL-6455, November-December 1961), S. Wexler and N, J e s s e .

THEORETICAL PHYSICS, GENERAL

V - 1 . The Deformation Energy of a Charged Liquid Drop (ANL-6432, September-October 1961), S. Cohen and W, J . Swiatecki.

V - 3 . Dynamics of Nuclear Collective Motion (ANL-6517, F e b r u a r y - M a r c h 1962), D. R. Ingl is .

V-4 . Relat ive (3-Decay Probabi l i t ies for ^gK-^o (ANL-6455, November -December 1961), D. Kurath .

V - 8 . Relationships of Collective Effects and the Shell Model (ANL-6358, Apr i l -May 1961), D. Kurath .

V - 9 . In terpre ta t ion of Exper iments Involving Excitat ion of the 15.1-MeV Level of C i2 (ANL-6391, July-August 1961), D. Kura th .

V-15 . Sta t is t ica l P r o p e r t i e s of Nuclear Energy States (ANL-6488, January 1962), N. Rosenzweig.

V-25 . Scattering of Alpha P a r t i c l e s by a Vibrational Nucleus (ANL-6517, F e b r u a r y - M a r c h 1962), L . J . T a s s i e .

V-33 , Flux Quantization and T ime-Reve r sa l Degeneracy (ANL-6517, F e b r u a r y - M a r c h 1962), M. Peshkin and W. Tobocman.

V-42 . Time Reve r sa l and Superselect ion (ANL-6488, January 1962), H. Eks te in .

V-46 . E las t i c Nucleon-Nucleon Scattering at High Energ ies and Small Angles (ANL-6517, F e b r u a r y - M a r c h 1962), K. Hilda.

1-22-18

I, EXPERIMENTAL NUCLEAR PHYSICS

1-22-18 Scat ter ing of Charged Pa r t i c l e s (51210-01)

H, W. Broek and J . L. Yntema Reported by H, W, Broek

INELASTIC SCATTERING OF ALPHA PARTICLES BY NUCLEI

IN THE REGION FROM Fe54 to Zn^s

The e las t ic and inelast ic scat ter ing of 43-MeV alpha

pa r t i c l e s by nuclei in the region from Fe^* to Zn®^ has been studied at

the Argonne 60-in. cyclotron. Targe t s studied were Fe^^*;, Mn^s, Fe^'^,

Niss^ CoS9, NiSO, Cu'33, Zn^^^ Cu^s^ and Zn^s . The alpha pa r t i c l e s

were detected by silicon su r face -ba r r i e r de tec tors . The line width was

about 1. 0% of the alpha energy.

The angular distr ibut ions for elast ic and inelast ic s ca t t e r -o

ing show the fanailiar pa t te rn of oscil lat ions with a period of about 10

and an envelope (a line drawn through the success ive maxima) which de­

c r e a s e s monotonically with increas ing angle. All of the ta rgets show

a group at about 1 MeV whose oscil lat ions a re out of phase with those

of elast ic sca t te r ing . F o r the even-even targets this group is due to the

2 f i r s t excited s tate , which is believed to be descr ibable as a one-phonon

osci l lat ion. F o r the odd-A ta rge t s this group shows an angular d i s t r ibu­

tion which is quite s imi la r to that seen for the even-even t a rge t s .

Hence, an i - Z osci l lat ion is also excited in those t a rge t s , and this

osci l lat ion couples to the spin I of the ground state to produce 21 + 1 or 1

2i + i levels (whichever is l e s s ) . The number of known levels at roughly 1 MeV is consis tent with this expectation (for the odd-A ta rge ts studied) except for Mn^^ " Mn^^ only four levels a r e known in the

1 Nuclear Data Sheets, National Academy of Sciences^, National

R e s e a r c h Council, 1959 (U. S. Governnaent Pr in t ing Office^ Washington, D. C, ),

1-22-18

i-MeV region, whereas five a r e required by the above interpretat ion, 7 _

Poss ib ly the — f i rs t excited state at 0, 126 MeV may belong to this quin­tet, or a l ternat ively there m.ay be a level which has not yet been observed.

6

5 —

•r 4 m

E

3 - -

b

Figure 1 plots the in­

tensity of the f i r s t inelast ic group

as a function of A. No regular

variat ion with A is found. Also, no

shell effects for protons is found

since the Ni points a r e intermediate .

A shell effect for neutrons may

exist since the Fe^* point is the

lowest of the even-even nuclei . A

definite odd-even effect is seen:

the points for odd-A nuclei a re

generally lower than those for even-

even nuclei . The lowest c ros s

section is that for Mn'='5, This low

c ros s section may be related to the

fact that the ground-sta te spin of

this nucleus is not what is expected

from simple shel l -model theory.

All of the nuclei studied show one or more strong groups

at about 3 - 5 MeV excitation. The angular distr ibutions of these groups

a re in phase with elast ic scat ter ing and have the appearance expected

for 3 groups. One group is seen in each of the even-even nuclei, while 2

four groups a r e seen for Cu®^ and Cu^'^. Since the ground-state spins 3 "

of Cu®3 and Cu®^ a re — , the four groups (21 + 1 = 4) a r e presumably

-

i

°~

h —

I

1 1 1

i

1

FIRST INELASTIC GROUPS CROSS SECTION PEAK AT flc=4r

' 5

I

I 1 .

i

' f

i X Mn • Fe 0 i i A Co V Cy - Zn

1

1

(« .o l

AT

1

-

^

—

""

I —

54 58 62 66

Fig. i . Cross sections f o r i =2 f i rs t inelast ic group at the maximum near 41°.

J . Saudinos, R. Beurtey, P . Catillon, R. Chaminade, M. Crut, H. Faraggi , A. Papineau, and J. Thirion, Compt, rend. 252, 96 (1961).

1-22-18 I - 3 i - i

E

•a

the coupling of a 3 osci l lat ion

to the ground s ta te .

F igure 2 com­

pa res the intensity of the 3 in­

elast ic groups at corresponding

maxima in their angular d i s ­

t r ibut ions. The maxima chosen

for compar ison a r e those that

occur near 35 in a l l c a s e s .

Fo r the odd-A ta rge t s , cont r i ­

butions from all of the 3

groups were combined. Even-

even targets generally show a

higher c r o s s section for 1 = 3

excitation than do the odd-A t a rge t s . This effect is s imi lar to what is

observed for 1 = 2 excitation (Fig. i ) . In addition, both even-even and

odd-A targets show that the c ros s section f o r i =3 excitation inc reases

with A. Fo r the i = 2 excitation no such tendency was found.

4

3

?

1

n

1 • 1 ' 1 __ L=3 GROUPS

CROSS SECTION AT PEAK AT

flg^ 35a

i

I I i •

i^

1 . 1 , 1

I

'

I I

1

{

X

• 0

A

¥

•

1 ' T

1 —

i -

-

Mn Fe i i Co — Cu Zn -

1 . 54 58 62 66

Fig . 2. Cross section for the 1 = 3 collective groups at the maximum near 35°.

I -31- i Elast ic Scattering of Protons

L. L. Lee, J r . and J. P . Schiffer

(51210-01)

Angular distributions of e last ical ly sca t te red protons have

been measu red with 8-MeV protons from the Argonne tandem Van de

Graaff genera tor . The protons were sca t te red from self-supporting foils

of Ca, Ni^s^ NiS", Cu^s, and Cu®5. An i8 - in . scat ter ing chamber

designed by T. H. Braid was used. The detector , a silicon surface-

b a r r i e r counter, could be rotated on a remotely controllable a r m with a o

prec is ion of 0. 1 . The beam was coUimated to a diameter of 0, 06 in.

1-31-1

1000

500t-

100

50

10

- 1 — I — I — 1 — r

Ca^''(p,p)Ca^°

Ep = 8MeV

30 so 90 120 LABORATORY ANGLE

150

F i g . 3 . E l a s t i c s c a t t e r i n g of 8-MeV p r o t o n s f r o m Ca .

and t a r g e t c u r r e n t s of 0. i [xA w e r e

e a s i l y ob ta ined . M e a s u r e m e n t s

w e r e m a d e a t 4 i n t e r v a l s b e t w e e n

30 and 165 to the inc iden t b e a m .

P r e l i m i n a r y r e s u l t s

a r e shown in F i g s . 3 and 4. We

hope to s tudy t h e s e a n g u l a r d i s t r i ­

but ions a t s e v e r a l e n e r g i e s , p a r ­

t i c u l a r l y above and be low the (p, n)

t h r e s h o l d s for the Ni i s o t o p e s . A

r ®

lOOOOt^,

ELASTIC SCATTERING OF 8 MeV PROTONS

! • • • • l~ @ ®

Ni

o u m lOOU

m m

2 o

>

<

10

Ni 60

Cu' S3

• •«•,<

Cu' ,65

_L 30 60 90 120 150

LABORATORY ANGLE

F i g . 4. E l a s t i c s c a t t e r i n g of 8-MeV p r o t o n s f r o m Ni^B^ Ni"'", C u ^ s , and Cu®s.

few m e a s u r e m e n t s wi th a w e i g h e d t a r g e t wi l l a l s o e s t a b l i s h an a b s o l u t e

c r o s s - s e c t i o n s c a l e for t h e s e da t a . We hope to fit the da ta wi th the

op t i ca l m o d e l and to s tudy the ef fects of chang ing r a d i u s a n d n e u t r o n e x ­

c e s s . It i s a l s o hoped that r e l i a b l e a b s o l u t e c r o s s s e c t i o n s for e l a s t i c

s c a t t e r i n g f r o m Cu a t e n e r g i e s a r o u n d 8-10 MeV wi l l he lp to r e s o l v e the

d i s a g r e e m e n t s b e t w e e n d i f fe ren t m e t h o d s of m e a s u r i n g t o t a l r e a c t i o n

c r o s s s e c t i o n s .

We would l ike to acknowledge the he lp of J . Wal lace a n d

F . P . M o o r i n g and the t a n d e m Van de Graaf f staff in m a k i n g th is e x p e r i ­

m e n t p o s s i b l e .

1-98-30

1-98-30 Unbound Nuclear Levels m the KeV Region (51210-Oi)

Car l T„ Hibdon

FLUORINE

A study of the unbound levels of F^^ has been continued.

The genera l fea tures of these levels and tentative analyses of some of the

levels up to about 150 keV neutron energy were given in previous r epo r t s . '

Some new data have been obtained m the regions of peaks Nos. 2 6, 12^

and 13 shown in F ig . 24 of reference 1, pa r t i cu la r ly in the wings of Nos,

Z and 6. The ent i re region from about 130-300 keV was also restudied.

The additional data were needed m the use of a recent ly developed method 2

of ana lys i s . Moreover , the energy dependence of the neutron scat ter ing 3

by the tantalum backing of lithium ta rge ts is now known. This cor rec t ion

has been applied to peaks Nos. 2, 6, 12, and 13 and to the peaks analyzed 2

by the method given by Hibdon and Monahan. The p a r a m e t e r s obtained

for these levels and other levels that could be analyzed a r e given m Table I.

Resonances in the 130-300 keV Region

The data obtained in the 130-300 keV region a r e shown in

Figs„ 5, 6, and 7. One sees many smal l peaks in Fig . 5 and many more

with l a rge r peak heights in F i g s . 6 and 7. A cor rec t ion for neutron

1 C. T. Hibdon, Phys ics Division Summary Report ANL-6326 |March

1961). p . 35.

2

C. T. Hibdon and J, E. Monahan, Phys ics Division Summary Report ANL-6432 (September - October 1961), p . 4.

3

C. T. Hibdon, Phys ics Division Summary Report ANL-6534 (Apr i l -May 1962), p . 25; Nuclear Ins t r . and Methods (to be published, 1962).

TABLE I. Levels of F^o der ived from neutron react ions with F^^ . The paranaeters J, i , and F a r e the values obtained as a best fit to the data. The p a r a ­m e t e r s for the s-wave levels used in the analyses a r e given a l so .

No.

1

2

3

4

5

6

7

8

9

10

11

12

13

30

43

44

48

E r

(keV)

15, 25

27.35

31.9

34.0

38.0

49. 7

70. 5

87,8

96.0

100.0

102.4

113. 2

121. 7

200.2

246.0

247.8

267.7

J

2

1

0

1

2

1

0

0

0

1

1

1

i

1

1

1

1

1

0

1

1

0

0

0

0

r (keV)

0.30

1. 70

4.00

5. 50

i. 10

3.00

1.20

1.00

2.0

1. 8

0,4

1.4

1-98-30

150 160 170 E„CkeV)

180 190

F i g , 5, N e u t r o n to t a l c r o s s s e c t i o n of f luor ine in the 130-190 keV r eg ion . The c u r v e shown by a so l id l ine d e p i c t s the t r e n d of the da t a ob ta ined by f la t de t ec t i on . Solid c i r c l e s r e p r e s e n t the da ta ob ta ined by s e l f - d e t e c t i o n . The loc i of the t h e o r e t i c a l s i n g l e - l e v e l p e a k he igh t s for J = 0, I = 0, 1 inc lude only e l a s t i c s c a t t e r i n g . C u r v e A r e p r e s e n t s the c o m b i n a t i o n of the p o t e n t i a l s c a t t e r i n g and the wings of s - w a v e l e v e l s .

s c a t t e r i n g by the t a n t a l u m b a c k i n g of the l i t h ium t a r g e t s does not i n c r e a s e 3

the heights of these peaks appreciably, A few of these peaks appear to

be due to s-wave levels . The curves that appear to fit the data for the

s-wave levels a r e shown in F i g s . 5, 6, and 7. All of the plots for s-wave

levels and the potential scat ter ing were combined to obtain the curves

labeled A in these figures. An at tempt was made to analyze the peaks 2

shown in F igs . 5, 6, and 7 by the method of Monahan and Hibdon. How­

ever, the difference between the theoret ical peak heights for successive

values of J is quite large and the peak heights obtained by the analyses

fail to come close to par t i cu la r values for any J, Rather, they fall more

8 1-98-30

2 so

Fig . 6. Neutron total c ro s s section of fluo­rine in the 184-244 keV region. The solid curve follows the t rend of the f lat-detection data. Points shown by solid c i rc les show the t rend of the se l f -de­tection data. The loci of the theoret ical s ingle- level peak heights for J = 0 and 1 include only elastic neutron scat ter ing. Curve A rep resen t s the combined contributions of the s-wave levels and the potential sca t ­ter ing.

or l e ss midway between the values for different J , Inelastic sca t ter ing 4

is known to begin in this region and is apparently strong enough to r e ­

duce the peak heights considerably. Hence, T K T ior each peak and

consequently the peak heights a r e reduced by the factor F /T. The

regions covered by F i g s . 6 and 7 exhibit peaks with l a rge r heights than

the ones shown in Fig . 5. However, the analyses still fail to yield peak

heights near theoret ical values for different J . The analyses do provide

tentative sets of p a r a m e t e r s for the levels shown in F igs , 5, 6, and 7

but the values of the spins a r e ambiguous and undoubtedly lead to e r r o n ­

eous values for the widths and the values of I . Therefore , an analysis

of the resonances in the 130-300 keV region is deferred until a method

is devised to include a reasonable es t imate of the inelast ic sca t ter ing.

A paper on the unbound levels of F^*^ up to a neutron

energy of 300 keV is near ly ready to be submitted for publication.

J . M. F r e e m a n , Phys . Rev. 99, 1446 (1955).

1-98-30 9

240 250 260 270 280 E,(keV)

290 300

Fig . 7. Neutron t r ansmiss ion c ross section of fluorine in the 240-300 keV region. The solid curve shows the variat ion in the flat-detection data. Points shown by solid c i r c l e s were obtained by self-detection. The loci of the theore t ica l s ingle- level peak heights for J = 0-3 include only e las t ic neutron sca t te r ing . Curve A rep resen t s the combined contr i ­butions of the s-wave levels and the potential sca t te r ing .

IV-10-4 11

IV. PLASMA PHYSICS

IV-10-4 Morphology of High-Frequency P lasmoids (54100-01)

Alber t J . Hatch

INTRODUCTION

The morphology of gaseous d ischarges and p lasmas

has always been an important facet in the study of their bas ic

p r o c e s s e s and m e c h a n i s m s . Thus in the l i t e ra ture on dc glow

d i scharges t he re has evolved a set of h i s to r i ca l -desc r ip t ive names

for the var ious visible features of d ischarges including the familiar

positive column, F a r a d a y dark space , negative glow, Crookes dark

space , and o t h e r s . Measu remen t s of dc d ischarge p a r a m e t e r s ,

such as the spat ial dis tr ibut ion of charge density and potent ial ,

r evea l var ia t ions that can be cor re la ted with their visible s t ruc tu r e .

Since dc d i scharges have been studied r a the r intensively for over a

century , it i s not at a l l surpr i s ing that thei r morphological c lass i f i ­

cation is considerably m o r e advanced and wel l -es tabl i shed than that

of high-frequency d i scharges which have only been studied ra ther

sporadical ly since about 1925.

The purpose of the p resen t r epo r t is to present a

sys temat ic photographic study of high-frequency p la smoids , to

suggest a morphological nomenc la tu re , and to point out some

morphological cha rac t e r i s t i c s that a r e per t inent to the mechanisms

involved.

PLASMA DOMAINS

Corre la t ion of the plasmoid photographs with the

var ious high-frequency p lasma mechanisms is facilitated by the

12 IV-10-4

10

10 - MULTIPACTING o > < hi (L

< Z

O bi

(L Q.

10

10

f= l5 Me/8es,d = l§cm, DRY AIR ALUMINUM ELECTRODES.23cmDIA.

^

LOW-PRESSURE PLASMOIDS •

DARK-SHEATH PLASMOIDS

MAINTAINING POTENTIAL

HIGH-POWER NORMAL" PLASMA

BREAKDOWN-

-MODE 2 PLASMA

MEAN-FREE-PATH LIMIT

DIFFUSION PLASMA

-MODE I PLASMA

COLLISION-FREQUENCY TRANSITION

10 - 6 10 10 ^ 10

PRESSURE,mm Hfl

10 10

Fig , 8. High-frequency plasma domains . F r o m data for p lasmas p r o ­duced in an a tmosphere of dry a i r between aluminum e lec t rodes , 23 cm in diameter and 15 cm a p a r t , by rf potentials at a frequency of 15 M c / s e c .

revised domain map shown in F ig . 8. This map r e p r e s e n t s a wel l -

smoothed plot of severa l hundred observations made during the past

three y e a r s . Never the less there a r e st i l l some unmapped a r e a s , mainly

in t ransi t ion zones where ins tab i l i t i es , detuning, and e r r a t i c nonrepro -

ducibility all combine to make observat ions difficult. Also miss ing from

this map is a fine s t ruc ture of subdomains , especially in the plasmoid

r eg ions , which a r e definitely present but have not yet been reproducibly

delineated.

The map will not be d iscussed in detail he r e . However , 2

in order to re la te to a previous set of photographs it is appropr ia te to

Fo r an ea r l i e r vers ion see F ig . 6 in Physics Division Summary Repor t , ANL-6262, December I960, p . 17-28. 2

Ibid . , F ig . 7.

IV-10-4

point out that the Mode I and Mode II p lasmas refer to the singly- and

doubly-s t r ia ted p lasmas at p r e s s u r e s of i 3 |j, and 50 (j,, r espec t ive ly ,

in reference 2, Consis tency indicates that p lasmas of the diffusion

type , with two bright s t r ia t ions near each electrode plus a third

cent ra l ly- located s t r ia t ion (usually of a different color and s t ruc tu re ) ,

as i l lus t ra ted at 350 (j, and 90 [j, in re ference 2, should be called the

Mode III p l a s m a s .

One other comment pert inent to the present use of the

domain map is that the p lasmoids occur at p r e s s u r e s of the order of

1 to 2 decades below the mean- f r ee -pa th l imit and the collision f re -3

quency t rans i t ion as d iscussed by Brown and MacDonald. Although

originally applied only to the diffusion mechanism of breakdown, these

two concepts a r e neve r the le s s of considerable significance for p l a s m a s .

The mean - f r ee -pa th liinit is defined as the condition in which the

e lec t ron mean- f r ee -pa th is equal to the cha rac te r i s t i c diffusion length 4

of the p lasma tube. F o r a i r , the data of Herlin and Brown indicate

that the lower p r e s s u r e l imit for the diffusion breakdown miechanism

to be operat ive in the p r e sen t tube should be at 7.6 |j.. The coll ision-

frequency t rans i t ion is defined as the condition in which the e las t ic

collision frequency between e lec t rons and atoms is equal to the radian

frequency of the applied field. F r o m data obtained by Rose and 5

Brown, again for a i r , this t rans i t ion should occur in the p resen t

tube at 22 jj,.

3

S. C. Brown and A. D. MacDonald, Phys . Rev. 76, 1629 (1949). 4

M. A. Herl in and S, C. Brown, P h y s . Rev. 74, 291 (1948). 5

D. J . Rose and S. C. Brown, J . Appl. Phys . 28, 561 (1957).

IV-iO-4

PLASMOID TERMINOLOGY

s R. W, Wood, in his c l a s s i c paper on high-frequency

p lasmoids , r epor ted two types of plasmoid: a spheroidal type of high

luminosity (bright green in pure O^)^ and a lenticular type which was

l ess luminous (pale g reen in O^). Although the order in which they

appeared as a function of rf potential depended on the excit ing-electrode

system being used , the t rans i t ion from one type to the other was

consis tent ly abrupt . Another cha rac t e r i s t i c common to both types

was that each appeared to be surrounded by a nar row dark sheath.

The p resen t observat ions indicate that the spheroidal

plasmoid is the only one that exhibits the dark sheath, that the

darkness is re la t ive ra ther than absolu te , and that the degree of

darkness depends on the conditions under which the plasmoid is formed.

The spheroidal da rk - shea th plasmoid can occur through a modera te ly

wide range of p r e s s u r e s and applied rf potentials as shown in F ig . 8.

The lent icular plasmoid occurs through a much n a r r o w e r range of

these p a r a m e t e r s and exhibits no dark sheath . It is mos t likely that

Wood's observat ion of a dark sheath for the lent icular plasmoid was

due in par t to e lec t rode and discharge- tube configurations different

from those used in the p resen t work . The location of the smal l

domain of the lent icular plasmoid with r e spec t to that of the da rk -

sheath plasmoid is the r ea son for the name l o w - p r e s s u r e p lasmoid.

The t e r m s "da rk - shea th" and " l o w - p r e s s u r e " allude to m o r e bas ic

p roper t i e s of the plasmoids than do the t e r m s "sphero ida l" and

" len t icu lar" which r ep re sen t a shape p a r a m e t e r that is dependent

mainly on configurations of the e lec t rodes and p lasma tube.

R. W, Wood, P h y s . Rev. 35, 673 (1930).

IV-iO-4 15

DARK-SHEATH PLASMOIDS

All the plasmoids photographed and descr ibed here were

establ ished in dry a i r between plane para l le l aluminum electrodes 26 cm

in d iameter and 15 cm apar t at a frequency of 15 M c / s e c . Panchromat ic

film (Kodak Royal Pan) was used in a Speed-Graphic camera at f / 7 .7 .

Most exposures were at 10 s ec . Because of the wide range of luminosit ies

encountered, no attempt was made to maintain a sys temat ic density scale

among different photographs. The main cr i ter ion was a set of prints

acceptable for half-tone reproduct ion.

A photograph of a typical dark-shea th plasmoid is shown

in F ig . 9. The essent ia l features of this photograph, as shown by the

drawing in F ig . 10, a r e (A) the main body

of the plasmoid (whitish in air) , (B) the

nar row dark sheath which gives the plasmoid

its n a m e , and (C) the wider Debye sheath

that extends to the e lec t rodes and tube wal ls .

The e lect rodes a r e on the left and right

edges of F i g s . 9 and 10.

Semiquantitative information

on the luminances of the var ious components

of the plasmoid can be obtained from density

m e a s u r e m e n t s . A set of such measurements^

made from the original negative used for

F ig . 9 is shown in F ig . i i . The resolution

of the densi tometer was approximately a

tenth of the width of the dark sheath, but

there is an appreciable amount of "noise"

due par t ly to the c i rcumstance that the

ape r tu re of the densi tometer was a

F ig . 9. Photograph of dark-sheath plasmoid. Plane para l le l disk electrodes located on left and right sides of photograph. Frequency = 15 M c / s e c , electrode separation = 15 cin, p r e s s u r e = 0.3 [j. in dry a i r .

A. J . Hatch, Proceedings of the Fifth International Conference on Ionization Phenomena in Gases (North Holland Publishing Company, A m s t e r d a m , 1962), Vol. I , p . 748.

IV-10-4

F ig . 10. Cross - sec t iona l drawing of a da rk - shea th plasmoid: (A) the main (luminous) body of the plasmoid; (B) the dark sheath; (C) the Debye sheath extending to the e lec t rodes (left and right) and the plasma tube walls (top and bottom).

I5em ELECTRODES

Fig . 11 . Density of neg­ative for plasmoid photograph in F ig . 9. Scale applies direct ly only to t r ace A. The subsequent t r a c e s B - F have each been succes ­sively ra i sed by approx­imately 0,18 density unit to avoid overlapping.

I V - i O - 4 17

pinhole r a t h e r t han a s l i t . F o r fac i l i ty in i n t e r p r e t i n g the d e n s i t o m e t e r

m e a s u r e m e n t s b e l o w , the t r a c e a long the z ax i s (axis of s y m m e t r y of the

p l a s m a tube and p l a s m o i d ) h a s b e e n r e d r a w n in F i g . 12 wi th m o s t of the

s p u r i o u s i r r e g u l a r i t i e s s m o o t h e d

out . H e r e i t h a s been a s s u m e d t h a t

the d e n s i t y D of the n e g a t i v e can be

r e p r e s e n t e d by

1.4

r 1.0

D = log^^ (i + a L ) , (1) I 2 0 .8 -

w h e r e L. i s t h e l u m i n a n c e of the

p l a s m a glow and a i s a n o r m a l i z i n g

c o n s t a n t .

A . Ma in Body of P l a s m o i d

J3

< w" 0.6-o z <

Zj

="T\

_ L

—

-

Zo

•K N /

/ \ / L \

/ , \ .^f - L B 2

, 1 F

,

1 i I

k

\

_J

-

.

.—1

--, _

\

0.3

kJ O

0.2

2 4 6 8 A X I A L POSIT ION, Z

o°-

F i g . IZ . L u m i n a n c e of the p l a s m o i d shown in F i g . 9 t a k e n f rom d e n ­s i ty t r a c e of F i g . I L L T ^ J i s the l u m i n a n c e of the Debye s h e a t h ;

T h i s s p h e r o i d a l

r e g i o n t e r m i n a t e s s h a r p l y wi th in

a p p r o x i m a t e l y a m i l l i m e t e r , i . e . ,

with in l e s s t han 0. 001 of an e l e c t r o n

m e a n - f r e e - p a t h ( M . F . P . « 50 cm in

a i r a t 1 fj.). T h i s is shown by the

s h a r p r i s e in the dens i t y t r a c e on

the i nne r s ide of PLASMOID

BOUNDARY in F i g . 1 1 . B y w a y

of c o m p a r i s o n , t he b o u n d a r y dep th

of the m o r p h o l o g i c a l d i v i s i o n s ( such

a s t h e n e g a t i v e glow) in a dc glow d i s c h a r g e i s of t h e o r d e r of one e l e c t r o n

m e a n - f r e e - p a t h . The s a m e i s t r u e of the s t r i a t i o n s in the h i g h - f r e q u e n c y

d i f fus ion- type p l a s m a s , such a s Mode II and Mode III . I t h a s no t ye t been

p o s s i b l e t o e v a l u a t e t h e l u m i n a n c e of the p l a s m o i d body e i t h e r d i r e c t l y o r

L p and L-g^ ^^^ ^'^'^ l u m i n a n c e s of the p l a s m o i d body and Debye s h e a t h a s d i s c u s s e d in the t e x t . The ha t ched c r e s c e n t r e p ­r e s e n t s the finite l u m i n a n c e of the d a r k s h e a t h . C o o r d i n a t e s z-and ZQ a r e the ax ia l pos i t i ons of the i n n e r and ou t e r edges of t h e d a r k shea th on the a x i s . T h e m i d p l a n e i s a t 0 and the e l e c t r o d e i s at 7 .5 c m .

IV-iO-4

indi rec t ly . T r i a l calculations with values of luminance from the Debye

sheath background (as indicated by LT,^ in F ig . iZ), and with cor rec t ions

for the shapes of the p l a smo ids , show that the luminance is constant to

within Z-3% throughout the main body of the p lasmoid .

The uniform luminance of the main body of the plasmoid

and its sha rp te rminat ion at the boundary can both be shown to be

plausibly consistent with the a s sumed plasmoid mechan i sm. The

presen t concept of this mechan i sm is that it is dominated by longitudinal

e l ec t ron-p lasma osci l lat ions of two types . One type is the c lass of

axially nonsymmetr ic osci l la t ions which can be driven by the applied

rf potential; the other type is the c l a s s of axially and rad ia l ly symmet r i c

oscil lat ions which can not be driven by the applied rf potent ia l , but which

possibly can. be excited by cross-coupl ing to the nonsymmet r ica l

oscillations»

One of the mos t in teres t ing and significant of Wood's

observat ions was that the spec t rum of this main body consis ts of both

a tomic and molecular l i nes , whereas the spec t rum of the sheath 8

regions contains only atomic l ines .

B . Dark Sheath

The dip in density at the dark sheath in F i g . 11 is

definite and consis tent , but not as g rea t as had been expected from

visual inspection of the plasmoid photograph and d i rec t observat ion

of the actual p lasmoid. S imi lar densograms of other plasmoid photos

show smal l dips such as these in some c a s e s , plateaus in o t h e r s , and

in a few cases only a smal l inflection at the dark sheath. Since in all

the photos the dark sheath appeared to be dark (in varying deg ree s ) ,

this outcome indicates that the re i s an "edge effect" optical i l lusion

R. W. Wood, Ph i l . Mag. 8, 207 (1929).

IV-iO-4 1

that enhances the dark appearance of the sheath when viewed by the

eye. A typical shape of the dip in luminance in the da rk - shea th region

is the s t ra ight segment with reduced or r eve r sed slope as shown

between z. and z in F ig . 12. If the luminance of the dark sheath I o °

were z e r o , the slope should change from negative on the right side

of z to infinity on the left s ide , then drop to finite positive values

as shown by the lower broken curve represen t ing the background

from the Debye sheath. Thus the hatched and c rescen t -

shaped a r e a on F ig . 12 r e p r e s e n t s the luminance due to the dark

sheath. The magnitude of this luminance is surpr is ingly large in

view of the apparent da rkness in the photograph of F ig . 9.

Three -d imens iona l viewing of an actual plasmoid

enhances the ^impression of da rkness of the dark sheath. H e r e , of

c o u r s e , the subjective nature of unaided vision is highly suspect

and one 's impres s ions mus t be evaluated carefully. However ,

d i rec t vision has the added advantage of being binocular and also

can incorpora te r ece ive r scanning, i . e . , moving the head around

to gain an impress ion of shape . This capability shows unequivocally

that the dark sheath i s a continuous three-d imens iona l shell that

completely sur rounds the p lasmoid.

A proposed explanation of the dark sheath is that it

r e p r e s e n t s a nar row zone in which the net rf E field (due to super ­

position of the applied E field and that developed by electron T 9

osci l la t ions in the plasmoid) pa s se s through a ze ro value . '

C. Debye Sheath

The identification of the region C in F ig . 10 as a

Debye sheath is based on the following considerat ions and m e a s u r e m e n t s .

9

Phys ics Division Summary Repor t , ANL-6376, June 1961, pp,36-46.

IV-10-

The axial length of the Debye sheath in the plasmoids is observed to be a

function of both applied rf potential and of p r e s s u r e through l imited ranges

of these p a r a m e t e r s . In F ig . 13 the length of the Debye sheath (axial)

depends strongly on V at 0.2 jj, but not at 0. 35 \i. This dependence at

0.2 jjL is shown by the log-log plot in F ig . 14. The dependence of the

Debye sheath on p r e s s u r e is shown in the photos of F ig . 15 and the plots

nzv

76V

52V

10 8 -

6

S L O P E " I

f = l6Mc/cmt d~ 15cm P = 0.20/4 Hg

_j I I 1 I < 10 20 40 60 too 200 5 APPLIED POTENTIAL, R F

PEAK VOLTS

F i g . 14. Axial length of Debye sheath in dark-shea th plasmoids as a function of applied rf potential. The data were de t e r ­mined from photographs, th ree of which a r e shown at 0 .2 jj, p r e s s u r e in F ig , 13.

0.2/4 0 .35 / i

Fig . 13. Photographs of da rk -sheath p lasmoids . Elec t rodes a r e identifiable on left and r ight sides of each photo by reflected light from plasmoid. Elec t rode separat ion =15 cm, applied frequency = 15 M c / s e c , p r e s s u r e s and applied rf potentials as in ­dicated.

IV-10-4 21

0.7/i 2.0/i

Fig . 15. Photographs of da rk - shea th p lasmoids . Elec t rodes a re ident i­fiable as in F ig , 13. Elect rode separat ion = 15 cm, applied frequency = 15 M c / s e c , applied rf potential = 81 V, p r e s s u r e s as indicated.

of F ig . 16, Thus in the range of rf

potentials and p r e s s u r e s considered ^

h e r e , the + -g and - ^ slopes in

F i g s . 14 and 16, respec t ive ly ,

indicate that the length of the

10

f s

0.5

Debye sheath is proport ional to 1 / 2

(V^,/P)

X

-1—I I I I 111 1 1—I I' r T"n I 1 1—I I I 1 I

'SLOPE — l / g ^ ^

According to theory , II

the length of the Debye-Huckel

shielding distance can be wr i t -1 0

ten as

0.21 ! o.oz

-J—i_La_uJ I I I I I M.I -J I ' ' ' • ' •

0.1 10

^D 6 .9 (T /n )

1 / 2 (2)

where T and n are the electron

t empera tu re (Maxwellian) and

PRESSURE. mmHg

Fig, 16. Axial length of Debye sheath in dark-shea th p lasmoids , plotted as a function of p r e s s u r e . Open c i rc les r ep resen t data from photographs, four of which a re in F ig . 15, applied rf potential = 81V. Grosses represen t data ob­tained by d i rec t visual observation of p lasmoids , applied rf potential = 76 V. Frequency - 15 Mc / sec and electrode separat ion =15 cm for all data.

e lectron densi ty , respec t ive ly .

Now it is certainly plausible that the electron tempera ture inc reases as

the applied rf potential i n c r e a s e s , but the functional relat ion between these

1 0 L. Spi tzer , Physics of Fully Ionized Gases (Interscience Pub l i she r s ,

Inc. , New York, 1956), p, 17.

IV-10-4

two p a r a m e t e r s is not known for the plasmoid case . However , a l inear

dependence can be assumed as a f i r s t -o rde r approximat ion. It is a lso

plausible that the e lect ron density i nc r ea se s as the p r e s s u r e i n c r e a s e s ,

but here a lso the functional re la t ion is not known. Again , however ,

a l inear dependence can be a s sumed as a f i r s t - o r d e r approximat ion.

If one now admi ts these two f i r s t - o rde r l inear approximations over

a suitably l imited range of p a r a m e t e r s , then it is possible to identify 1 / 2

the observed dependence on (E /p) with the theore t ica l Debye-

Huckel dependence on (T/n) ' as in Eq. (2). This tenuous a rgument

is the bas i s for the tentative identification of this sheath as a Debye

sheath. This argument actually holds up quite well on a quantitative

b a s i s . T h u s , if the plasmoid has an e lec t ron t empe ra tu r e of o , l i

150 000 (corresponding to an e lect ron energy of 15 eV ) and a 1 2 Q

cutoff e lect ron density of 2. 78 X 10 cm~3 (corresponding to the

applied frequency of 15 M c / s e c ) , the length of the Debye sheath is

X. = 1 . 6 cm. This cor responds to the axial length of the sheath

at a p r e s s u r e of about 1 [x in F i g . 16,

In the photographs in F i g s . 13 and 15, it i s evident

that at the higher p r e s s u r e s and potentials the luminance of the

Debye sheath is high and tends to obscure the dark sheath. F r o m

the photographs in F ig , 15 it appears that the width of the dark

sheath i n c r e a s e s slightly as the p r e s s u r e is reduced. In the

range of very low rf potential near the maintaining boundary for

the da rk - shea th plasmoids;, the dark sheath evidently d i sappears

as shown in the two bottom f rames of F i g . 13. Although the reason

for this is as yet unknown, it is suspected that what actually happens

is that e i ther the Debye sheath d i sappears or that the Debye sheath 1 1

E. R, H a r r i s o n , J , E lec t ron ics and Control 5_, 319 (1958), 1 2

R, G e l l e r , Compt, rend , 249, 2749 (1959).

IV-10-4 23

and the plasmoid dark sheath become ident ical . This question is unlikely

to be resolved until m o r e is learned about the features distinguishing

these two types of sheaths .

No enlightening information on the Debye sheaths has yet

been obtained from the density t r a c e s in F i g s . 11 and 12.

LOW-PRESSURE PLASMOIDS

Photographs of the lenticular type of plasmoid, s imilar to

those originally repor ted by Wood, a r e shown in F ig . 17. The t ransi t ion

123V 139V 159V Fig . 17. Photographs of l ow-pres su re p lasmoids . Elect rodes a re

located as in F i g s . 13 and 15. Elect rode separation = 15 cm, applied frequency = 15 M c / s e c , p r e s s u r e = 0. 15 |JL, applied rf potentials a re as indicated.

between these l o w - p r e s s u r e plasmoids and the dark-shea th plasmoids is

always abrupt , but the domains overlap because of p r e s s u r e h y s t e r e s i s .

That i s , at an rf input power at which the t ransi t ion with increasing

p r e s s u r e occurs at about 0,2 p,, the t ransi t ion with decreasing p r e s s u r e

occurs at about 0. i jj.. This t rans i t ion is indicated in Fig. 8 by the heavy

broken l ine. Studies of the e lec t r ica l cha rac te r i s t i c s show that those of

the l ow-p re s su re plasmoids a re ve ry s imi la r to those for multipacting.

IV-10-4

This is consistent with the photographs which show the l ow-p re s su re

plasmoid superposed on the fair ly uniform bluish but sheathless glow

typical of mult ipacting. It is a lso consis tent with the fact that this 1 1 1 2

type of plasmoid is not observed by Har r i son and G e l l e r , both

of whom use rf exciting fields incapable of producing mult ipact ing.

Densi tometer m e a s u r e m e n t s made on these plasmoids indicate that

the plasmoid dark sheath is not p resen t h e r e . The whitish glow of

the l ow-p re s su re plasmoids in a ir is ex t remely faint in comparison

with that of the da rk - shea th p lasmoids , and they usual ly can only be

seen when viewed edge-on in the rad ia l d i rec t ion . This is also in

contras t to the da rk - shea th plasmoids which a r e equally visible from

all d i rec t ions .

The l o w - p r e s s u r e plasmoid can be made to beconae

as thin as des i red (up to the abili ty of the eye to detect i t ) , and

under favorable c i r cums tances it has been observed in the form of

a wafer about 1 m m thick and 2 - 5 cm in d i ame te r . Thus it is more

in the nature of a ve ry tenuous s t r ia t ion ra the r than a p lasma entity.

It is possible that it may be a sor t of p r e c u r s o r of the da rk - shea th

plasmoid and that it competes weakly against mult ipacting a t these

low p r e s s u r e s .

HIGH-POWER PLASMAS

Above the da rk - shea th plasmoids there is an uncharted

t ransi t ion zone in F ig , 8 charac te r i zed by plasma instabi l i t ies that

a r e a t t r ibuted to an unknown combination of effects such a s mode

jumping, rf c ircui t detuning, and e lec t rode outgassing. This zone

can be c rossed m e r e l y by increas ing the input rf power sufficiently

and keeping the exciting c i rcui t as well tuned as poss ib le . The high-

power p lasmas produced by the high rf potentials (above 1 kV) and

IV-10-4 25

power of the order of severa l hundred watts have some of the visual

cha rac te r i s t i c s of both the da rk - shea th plasmoids and the Mode 1 p la smas ,

Photographs of these high-power p lasmas a r e shown in F ig , 18, At the

0.8 / i , 1530V r" ^

Fig . 18. Photographs of high-power p l a smas . Elec t rodes are located as in F i g s . 13, 15, and 17. Elec t rode separation = 15 cm, applied f re ­quency = 15 M c / s e c . p r e s s u r e s and applied rf potentials a re as indicated.

lowest p r e s s u r e (0.8 |j.) the plasma boundary is very poorly defined. At

the in termediate p r e s s u r e s (2.2 [i and 4.0 |j.) the left side appears to be

quite well defined but the right side is diffuse. This is because the

camera was purposely located off-center in order to show the extreme

sharpness of one of the boundar ies . The boundaries a r e actually the same

on both s ides , a r e ext remely sha rp , a re very near ly flat, and give the

plasmia the appearance of a brightly glowing slab. There is no comparable

radia l boundary and the plasma extends a lmost continuously to the radial

edge of the d ischarge tube where the nonuniform thickness of the pyrex

walls obscures the details for tangential viewing angles . It is mainly for

this reason that these p lasmas a r e not considered to be p lasmoids . Com­

par ison of the s t ruc ture of these plasmas with that of the dark-shea th

plasmoids indicates that the symmet r i c type of e lec t ron-plasma oscillation

does not occur in the high-power plasma and that the nonsymmetr ic

26 IV-10-4

oscil lat ions a r e the only type that do occur . This high-power plasma

has been tentat ively called "normal" because the in te rna l rf field is

me re ly at tenuated ra the r than r e v e r s e d as in the case of the da rk-9

space p lasmoid.

V - 1 2 - 1 Z7

V. T H E O R E T I C A L P H Y S I C S , G E N E R A L

V - i 2 - l S e n i o r i t y Mixing in I f ^ . 2 Nuc le i (51210-01)

R, D . Law son and B , Z e l d m a n

1 2 F o r t a r g e t n u c l e i in wh ich the If^yg n e u t r o n s h e l l i s

f i l l ing , *' i t h a s b e e n found tha t m o r e t han one p r o m i n e n t i = 3

t r a n s i t i o n i s o b s e r v e d in n e u t r o n p i ckup r e a c t i o n s . On the b a s i s of

a l l the d a t a , one can show tha t a s c r i b i n g e a c h of the peaks t o a

d i f fe ren t o r b i t a l does not p r o v i d e a sa t isfa-ctory exp lana t ion of t h e

r e s u l t s . If the wave func t ions d e s c r i b i n g n u c l e i in which t h e If., ,3

s h e l l i s f i l l ing w i th n e u t r o n s and p r o t o n s have w e l l - d e f i n e d i s o t o p i c

sp in and s e n i o r i t y , then t h e (d , t ) p i ckup r e a c t i o n on an e v e n - e v e n

t a r g e t should p o p u l a t e only two l e v e l s wi th i = 3 in the odd-A

d a u g h t e r , n a m e l y , t h e I = •g' s t a t e s wi th s e n i o r i t y one and i s o t o p i c

sp in T ± g-. If the u s u a l m o d e l of p i ckup r e a c t i o n s i s t o be r e t a i n e d ,

t hen a r e a s o n a b l y s a t i s f a c t o r y a n a l y s i s of t h e r e s u l t s i s p o s s i b l e

p r o v i d e d s e n i o r i t y i s not a good q u a n t u m n u m b e r in the i£ .^ s h e l l

( i . e . , the n u c l e a r s t a t e s have m i x e d s e n i o r i t y ) . Al l t he s t r o n g

i = 3 t r a n s i t i o n s o b s e r v e d m a y then be c o n s i d e r e d a s a r i s i n g p u r e l y

f r o m p ickup of I f - , ,2 n e u t r o n s .

An a l t e r n a t i v e to t h e s e n i o r i t y c l a s s i f i c a t i o n for 3

n u c l e a r s t a t e s i s p r o v i d e d by the E l l i o t t g e n e r a t i n g p r o c e d u r e .

In t h i s m e t h o d , the l o w e s t e n e r g y e i g e n v e c t o r of spin I i s a s s u m e d

to be g iven by

1 J , L . Y n t e m a , P h y s , R e v . (to be p u b l i s h e d ) .

2 B , Z e l d m a n and T . H, B r a i d , B u l l . A m . P h y s . Soc , 7_, 315 (1962),

J , P , E l l i o t t , P r o c , R o y , S o c . (London) A 2 4 5 , 128 (1958) .

v - 1 2 - 1

z

where C , i s a normal iza t ion constant , D (R) is the rotat ion K • MK

m a t r i x , and the coordinate sys tem Rx is or iented with r e s p e c t to

the labora tory sys tem x. The N-par t i c le de terminant XT^ ^^ con-

st ructed by filling the lowest Nilsson orbits of the I f^/g shell for

eihter positive or negative deformation. On the bas is of wave

functions constructed in this way, fractional parentage coefficients

can be evaluated. The s t rengths given in Table II a r e propor t ional

to the squares of t he se coefficients.

The theore t ica l and exper imenta l r e su l t s a r e given

in the tab le . The calculations have been performed by generat ing

from both signs of the deformation as well as for the pure seniori ty

wave functions. The calculated values a r e for t r ans i t ions to the

lowest s ta tes of spin I in the final nuc leus . The exper imenta l r esu l t s a r e obtained from (d, t ) reac t ions init iated by 21.5-MeV

1 ^ 2 deute rons . *' There is good ag reemen t between the p resen t

calculations and the exper imenta l r e su l t s for mos t t r a n s i t i o n s .

The positive deformation usual ly is p r e f e r r ed . The m o s t flagrant

d isagreement is the t rans i t ion to the ground state of Ti**® (d, t )Ti ' i5;

but even he re the seniori ty value is no be t t e r . Fo r the Ti^s (d , t )Ti4s

reac t ion , both the mixed-sen io r i ty wave functions and the exper imenta l

data indicate that the bulk of the t rans i t ion s trength proceeds to s ta tes + + + +

other than the lowest 0 , 2 , 4 , and 6 s t a t e s . The sum of these

s t r eng ths , however , exhausts the sum rule for wave functions of

pure senior i ty . The amount of senior i ty mixing is d i rec t ly m e a s u r e d

by the Ti^O (d,t)Ti49 reac t ion , which shows the mixing to be about 50%.

TABLE II, Strengths of t r ans i t ions . The s t rengths of t rans i t ions to the lowest state of spin J in the final nucleus a r e calculated by use of wave functions generated from positive defor­mat ion , negative deformation, and senior i ty . The las t column l i s t s the exper imenta l value for these t r ans i t i ons .

<:

tSJ

Level in the final nucleus

Strength

Targe t Energy Spin + Deformation - Deformation Seniority Exper iment

Ti46

Ti47

Ti48

Ti49

Tiso

Cr52

Fe54

0

0,88

2.07

3,30

0, 16

0

0,98

2.33

3.30

0

0

0

7/2

2+

4+

6'^(?)

7/2"

0^

2+

4+

6'^(?)

7/2"

7/2"

7/2"

3.27

0.78

0.88

0,08

3.74

0.25

0,88

0.50

0,05

4.90

3,31

3,75

3 ,00

0 . 4 3

1,27

0 . 0 6

3 .67

0 . 2 5

0 . 4 5

0 . 8 2

1.37

4 . 9 0

4 . 2 3

5 . 5 2

3, 33

5 . 6 0

0 . 2 5

1.19

2 . 1 4

3 .09

7 , 7 1

7 . 2 0

6 . 0 0

2 . 1 5

0 . 5 7

0 . 8 6

0 . 1 3

2 . 4 5

0 , 2 3

0 . 6 8

0 . 5 4

(2. 30)

4 , 0 5

3 ,58

4 . 4 3

o

31

PUBLICATIONS SINCE THE LAST REPORT

PAPERS

TIME REVERSAL AND SUPERSELECTION H, Ekstein . . . . . . , . . , . . , . . . . , . . . (Pro jec t V-42)

Nuovo cimento 23 , 606-615 (February 1, 1962)

POLARIZATION OF NEUTRONS IN SCATTERING FROM LIGHT NUCLEI AND IN THE Li'^(p,n)Be'? REACTION

A, J , E l w y n a n d R . O, Lane . . . . . . . . . . . (Project 1-18) Nuclear P h y s . 31_, 78-117 (January 1962)

POLARIZATION AND DIFFERENTIAL CROSS SECTION FOR NEUTRON SCATTERING FROM SILICON

R, O. Lane , A. J . Elwyn, and A, Langsdorf, J r . . . (Project 1-18) Phys , Rev. _126, 1105-1111 (May 1, 1962)

ABSTRACTS

Abs t rac t s for the meeting of the American Physical Society, Evanston, I l l inois , June 1 9 - 2 1 , 1962.

N i4 (d , a )C i2 REACTION . . . . . . . . . . . . . . . . . (Project 1-25) R, G, A l i a s , T, H. Bra id , L. L, L e e , J r , , and J . P , Schiffer

Bull . Am. P h y s . Soc. 7, 411 (June 19, 1962)

ON THE FRAGMENTATION OF HYDROCARBONS UNDER HIGH-ENERGY ELECTRON IMPACT

J, E . Monahan and H. E , Stanton . . . . . . . . , (Project 11-40) Bul l . Am, P h y s . Soc. 7, 399 (June 19, 1962)

TWO RECENT ADVANCES IN SLOW-NEUTRON DETECTORS G, E . Thomas and L, M, Bollinger . . . . . . . (Project 1-2)

Bul l . Am. Phys , Soc. 7 , 411 (June 19, 1962)

ADDITIONAL PAPERS ACCEPTED FOR PUBLICATION

NEUTRON BACKGROUND DUE TO Ta BACKINGS FOR LITHIUM TARGETS

C, T , Hibdon , . . . . . . , , , , . . . . . . . . , (Project 1-98} Nuclear I n s t r . and Methods

A THIN dE/dx COUNTER WITH LARGE APERTURE J, A, Weinman and R. K. Smither . . . . . . . . (P ro jec t 1-16)

Rev. Sci. Ins t r , (June 1962)

PERSONNEL CHANGES IN THE ANL PHYSICS DIVISION

NEW MEMBERS OF THE DIVISION

Resident Resea rch Associa tes (Summer)

Dr . Calvin M. C l a s s , Associa te P r o f e s s o r , Rice Universi ty .

Measurement of l ifetimes of nuclear s ta tes by

recoi l methods . Came to Argorme on June 14,

1962. (Host: S. S. Hanna.)

D r . Suraj N. Gupta, Distinguished Professor of P h y s i c s , Wayne

State Univers i ty , Det ro i t , Michigan. Theory of

e lementary pa r t i c l e s . Came to Argonne on

June 18, 1962. (Host: M. H a m e r m e s h . )

Dr , Kurt J u s t , Associa te P ro fe s so r of P h y s i c s , Universi ty of

Ar izona , Tucson, Arizona; on leave from the

F r e e Universi ty of Ber l in . Gauge invariance in

e lect rodynamics and gravi tat ion. Came to Argonne

on June 1, 1962. (Host: M, H a m e r m e s h . )

Dr, Lu Sun Liu, Lec tu re r in P h y s i c s , Northwestern Universi ty,

High-energy par t ic le physics and complex angular

momenta . Came to Argonne on June 14, 1962.

(Host: M. H a m e r m e s h . )

Dr . Irving Michelson, P rofessor of Mechanical Engineer ing,

Illinois Institute of Technology, Studies of energy

t r a n s f e r s induced by radiofrequency discharge in

a i r . Came to Argonne on June 18, 1962. (Host:

A. J . Hatch,)

Dr. Bishan P . Nigam, Associa te P r o f e s s o r , Universi ty of Buffalo,

Spin-orbit in teract ion in nuclei . Came to Argonne on

May 3 1 , 1962. (Host: M. H a m e r m e s h . )

Dr . J . Reid P a t t e r s o n , P ro fe s so r and Head of Phys ics Depar tment ,

Rockford College. R e s e a r c h with the fast chopper.

Came to Argonne on June 6, 1962. (Host: L. M.

Bol l inger , )

D r . F r e d E . Stafford, Ass i s tan t P ro fe s so r of Chemis t ry , Nor th ­

wes te rn Univers i ty . Mass spec t romet r i c study of

the react ion of vapors with condensed phases at

high t e m p e r a t u r e s . Came to Argonne on June 13,

1962. (Host: J . Berkowi tz . )

Resident Resea rch Associa te (Post-Doctoral )

Dr . E . Brooks She ra , Ins t ruc tor in P h y s i c s , Western Rese rve

Univers i ty . Nuclear spectroscopy of shor t - l ived

radionucl ides . Came to Argonne on June 14, 1962.

(Host: S. B . Burson , )

Resident Student Assoc ia tes (Summer)

Mr . Allan D. Car l son , graduate student, U. of Wisconsin, Working

with T. H. Bra id on the development of so l id-s ta te

detectowand on g a m m a - r a y spect roscopy. Came to

Argonne on June 4 , 1962.

Mr. Rober t J . F r e i b e r g , graduate s tudent . Universi ty of I l l inois ,

Working with A. J . Hatch on exper imental inves t i ­

gations of high-frequency plasmias and p lasmoids .

Came to Argonne on June 6, 1962.

Mr . Harvey Leff, graduate student. State Universi ty of Iowa, Work­

ing with N. Rosenzweig on the s ta t is t ical theory of

energy leve l s . Came to Argonne on June 14, 1962.

Mr . J a m e s C. Pool , graduate student. State University of Iowa.

Working with J . M. Cook (AMD) on the mathematical

foundations of quantum field theory. Came to Argonne

on June 14, 1962.

Student Aides (Summer)

Mr . Timothy Ha r t , Knox College. Working with S. S. Hanna on

r e s e a r c h with the Moessbauer effect. Came to ANL

on June 12, 1962,

Mr . George Rieke , Oberlin College, Working with G. J . Perlow on

studies of the Moessbauer effect. Came to ANL on

June 7, 1962.

Mr . Gene Rugotzke, Wisconsin State College, Eau Cla i re . Working

with S. Wexler on the construction and use of a m a s s

spec t romete r for the study of the ionization and ex­

citation induced by very energe t ic , mass ive ions from

the Van de Graaff. Came to ANL on June 7, 1962,

M r . Br ian M. Sa lzberg , Yale Univers i ty . Working with R. K. Smither

and A. P . Magruder on the analysis of data on gamma

rays from neutron capture in Sm and T e . Came to

ANL on June 13, 1962.

Mr . Gene Sprouse , Massachuse t t s Institute of Technology, Working

with R. K. Smither on m e a s u r e m e n t s of capture gamma

rays from te l lu r ium with the b e n t - c r y s t a l spec t romete r

at C P - 5 , Came to ANL on June 13, 1962.

Mr . John B. Van Zytveld, Calvin College, Grand Rap ids , Michigan.

Working with J . L. Yntema on analys is of data on

(d,p) reac t ions on Ti and Bi and on the construction

of control devices for the 60-in. scat ter ing chamber .

Came to ANL on June 5 , 1962.

Mr . Ronald E . Z e l a c , Universi ty of I l l inois . Working with J . Berkowitz

on (1) setting up an exper iment to m e a s u r e the ionizing

efficiency of e lec t rons and /o r (2) studying the react ions

between excited or ionized meta l a toms and a gas as a

function of the pa r t i a l p r e s s u r e s , the ionizing vol tage ,

and the cu r r en t . Came to ANL on June 19, 1962.

Technician

M r . Louis J . Chir icot t i joined the Phys ics Division on June 19, 1962

as a R e s e a r c h Technician J r . with R. S. P r e s ton and

R. K. Smither .