This work was supported by the National Science Foundation Grant NSF PHY 81-14339 and by Indiana Universit

Becchetti, F.D.

Hicks, K.

Janecke, J.

Karwowski, H.J.

Kwiatkowski, K.

Lister, P.

Nadasen, A.

Zhou, S.

English

IUScholarWorks

were t o  s e t  B f z 0 . 8 3 ~ ~ ~ ~ ~  and af/a,=l.OO, a s  suggested 
f 
i n  Ref. 8, but us ing our  more s o p h i s t i c a t e d  l e v e l  
d e n s i t y  t rea tment ,  t he  ca l cu la t ed  af iss  would 
s u b s t a n t i a l l y  exceed the  measured values  a t  a l l  
bombarding ene rg ie s  f o r  a l l  t h ree  systems, and t h e  
fission-fragment a n i s o t r o p i e s  measured f o r  6 ~ i  + I g 7 ~ u  
would be overpredic ted  by -25%. 
We conclude t h a t  t he  d i f f e r i n g  claims i n  Refs. 6 
and 8 concerning high-spin f i s s i o n  b a r r i e r  he igh t s  f o r  
A-200 can be l a r g e l y  a t t r i b u t e d  t o  d i f f e r e n c e s  i n  the  
under lying assumptions and philosophy of the  
s t a t i s t i c a l  model analyses ,  although c e r t a i n l y  
d i f f e r e n c e s  i n  experimental  technique and i n  
con t r ibu t ions  from competing r e a c t i o n  mechanisms may 
f u r t h e r  cloud the  comparison. Our c a l c u l a t i o n s  
adequate ly  exp la in  the  measurements f o r  t h ree  widely 
d i f f e r i n g  ent rance  channels t o  A1200 CN, r e i n f o r c i n g  
our  e a r l i e r  conclusion6 t h a t  t h e r e  is no evidence, a t  
t he  present  l e v e l  of s o p h i s t i c a t i o n  of the  s t a t i s t i c a l  
t rea tment  f o r  an inadequacy of the  RLDM-NIFG s t r u c t u r e  
p red ic t ions  a t  high sp in  and e x c i t a t i o n  i n  t h i s  mass 
range. 
1) A. Gavron, Phys. Rev. C 21, 230 (1980). 
2) A. Zebelman e t  a l . ,  Phys. Rev. C 2, 200 (1974). 
3) F. P l a s i l  e t  a l . ,  Phys. Rev. Let t .  45, 333 (1980). 
4) M. Beckerman and M. Blann, Phys. Rev. C 17, 1615 
(1978). 
5) M. Blann and T. Komoto, Phys. Rev. C 24, 426 
( 1981). 
6) S.E. Vigdor e t  a l . ,  Phys. Rev. C 26, 1035 (1982). 
7) M.G. Mustafa e t  a l . ,  Phys. Rev. C 25, 2574 (1982). 
8) D.J. Hinde e t  a l . ,  Nucl. Phys. A385, 109 (1982). 
9) S.E. Vigdor and H.J. Karwowski, Phys. Rev. C 26, 
1068 (1982). 
190 MeV PROTON-INDUCED SYMMETRIC AND ASYMMETRIC FISSION* 
F. D. Becchet t i ,  J. Janecke and P. L i s t e r  
Un ive r s i ty  of Michigan, Ann Arbor, M I  48109 
K. Kwiatkowski, H.J. Karwowski, and S. Zhou 
Indiana Univers i ty  Cyclotron Univers i ty ,  Bloomington, Indiana 47405 
A. Nadasen 
Unive r s i ty  of Michigan-Dearborn, Dearborn, M I  48128 
K. Hicks 
Univers i ty  of Colorado, Boulder, CO 80309 
Proton-induced f i s s i o n  (Ep = 190 MeV) has been Energy s i g n a l s ,  and t iming s i g n a l s  r e l a t i v e  t o  the  
s tud ied  f o r  uranium and s e v e r a l  s e l e c t e d  nuc le i  wi th  A cyc lo t ron  r .f .  and between d e t e c t o r s  were used f o r  
between 140 and 210. F i s s i o n  fragments were de tec t ed  fragment i d e n t i f i c a t i o n ,  with energy and r e l a t i v e  mass 
i n  the  163 cm diameter s c a t t e r i n g  chamber us ing s p e c t r a  c a l i b r a t e d  us ing a t h i n  2 5 2 ~ f  i s s i o n  source.  
s o l i d - s t a t e  de tec to r s .  Typical ly  a s i n g l e  300 mm2 S i  The t ime-of-fl ight r e s o l u t i o n  of 0.7 t o  1.5 ns  (FWHM) 
d e t e c t o r  ( < l o o p )  was placed on one d e t e c t o r  arm was s u f f i c i e n t  t o  sepa ra t e  f i s s i o n  fragments from most 
(8=90°) about 15 cm from the  t a r g e t .  A th ree -de tec to r  of the  e n e r g e t i c  l i g h t  i ons  emit ted  and provide an 
a r r a y  (600 mm2 S i ;  < lo0  pm) was loca ted  about 30 cm approximate mass i d e n t i f i c a t i o n  (510 m u )  ( see  Fig. 1). 
away on an opposing d e t e c t o r  arm (8 < -90°), wi th  the  The t a r g e t s  cons i s t ed  of s e l f  -supporting r o l l e d  
t a r g e t  set a t  45' wi th  r e spec t  t o  the  inc iden t  beam. metal f o i l s ,  about 500 pg/cm2, o r  i n  the  case  of U, Eu, 
155 
MASS 
0 100 150 
MASS 
0 50 100 150 
Fig. 1 for Ce and Eu. These have been obtained by 
gating on the fragments ' time-of-flight and summed 
kinetic energy. The latter, to within a few MeV, 
follows the z2/A1I3 dependence expected for binary 
fi~sion.~ The data for 140ce indicates 
highly asymmetric fission (Figs. 1 and 2) at Ep=190 MeV 
even in the presence of high fission barriers. Our 
results appear to confirm those recently obtained at 
Ep = 600 MeV for A = 140 (Fig. 3). Similarly our data 
for Pr, Eu and Tb (i.e. A < 160) exhibit a very broad 
relative mass division (e.g. Fig. 1) possibly 
suggesting a Businaro-Gallone effect . The cross 
section data have been compared with statistical-model 
10 fission calculations modif ied5 to include pre-compound 
20 nucleon emission (Fig. 4). The data can be reproduced 
5 using standard fission-barrier and level-density 
10 
parameters, viz .  Bp = B~~~~ and aF = 1.05 a ~ .  
3 0 
0.0 0.5 1.0 0.0 0.5 4 .O A short paper describing the results of the first 
Mi / (M,+M2)  MI / (Ml+M2)  
phase of this work has been submitted for publication 
(Phys. Rev. C). A more complete analysis of all the 
Figure 1. Relative fission mass distributions deduced data is in progress. 
for the ~ A B  = 8~ - 0~ (lab) values shown, (8 = 90") 
assuming M1/(M1+M2) = E2/(El+E2). The angular 
acceptance of the detectors was 4". 
Lu, Ce, h. and Ba, chloride or fluoride compounds (~400 I- 
pg/cm2) evaporated onto thin carbon foils. The PrF3, I (3 
L - 
LuF3 and CeF3 material was obtained1 in ultra pure form ;? 
with parts heavy element contamination. Most of s I !  
the targets were also checked with X-ray fluorescence 
N 
(=lo'5 parts sensitivity). E g 
- 
Fragment kinetic energy spectra (El, E2, ... ) and I- 
partial angular correlations (,3 angles) were obtained 
for most of the targets near 0 = 90". Angular 
p + Ce - FISSION 
Ep=190 MeV = 2 COUNTS 
. = I COUNT 
.:* 
'**s. . - 
8 
. ..I m o o .  l o  . 
distributions were obtained for lS9~b, lg7Au and U, and E2/(E, +E2) 
are nearly isotropic. 
Relative fission mass spectra Figure 2. A two-dimensional spectrum displaying p+Ce 
fission fragment time-of-flight (relative to cyclotron 
[assuming M1/(M1SM2)=E2/(E1+E2)1 are displayed in r.f.) vs. E2/(E1+E2) [=M1/(M1M2)I. The data are 
consistent with Ml = 50 and M2 - 80. 
MASS 
0 35 70 105 140 
- 
0 35 70 105 z 
J 
w eAB= i70° 
c E,= 190 MeV 
Figure 3. A comparison of f i s s i o n  mass d i s t r i b u t i o n s  
observed f o r  Ep = 600 MeV ( top;  Ref. 3) and Ep = 190 
MeV ( t h i s  experiment ). 
'work supported by NSF con t rac t s  PHY78-07754 (UM) and 
PHY78-22774 (IU), and DOE contract  DE-AC02-81ER-4007 
(IU). 
1) Ames Laboratory, Iowa S t a t e  University,  Ames, IA. 
2) V. Viola, Nuclear Data +, 391 (1966). 
Figure 4. Resul ts  of s t a t i s t i c a l - m o d e l  f i s s i o n  
ca lcu la t ions  which include precompound nucleon emission 
with  a geometry-dependent hybrid model (Ref. 5). The 
curves correspond t o  the  following parameters: Sol id  
curves : &/7, = 1.05 with Bf = 0.7 B~ LDM (curve a ) ,  and 
Bf = Bf curve d ) ;  broken curves: af /a  = 1.00 with 
Bf = 0.7 B~~~~ (curve b) ,  = 0.85 B~~~~ (curve c )  and = 
1.0 B~~~~ (curve e). 
3) H.-A. Gustafsson, G. Hylten, B. Schroder, and E. 
Hagebo, Phys. Rev. C 24, 769 (1981). 
4) U.L. Businaro and S. Gallone, Nuovo Cimento 1, 629 
(1955); 1, 1277 (1955); J.R. Nix, Nucl. ~ h y s T e ,  
241 (1969). 
5) M. Blann, Program ALICE, Report COO-3493-29. 
- - 
unpublished; M. Blann, Phys. Rev. ktt. 28, 757 
(1972). 


190 MeV Proton-Induced Symmetric and Asymmetric Fission

https://scholarworks.iu.edu/dspace/bitstream/2022/2736/1/iucf_1982_155-157.pdf

190 MeV Proton-Induced Symmetric and Asymmetric Fission

Abstract

Similar works

Full text

Available Versions

IUScholarWorks