This research was sponsored by the National Science Foundation Grant NSF PHy 87-1440

Becchetti, F.D.

Brown, J.

Hicks, K.

Janecke, J.

Karwowski, H.J.

Kwiatkowski, K.

Lister, P.M.

Nadasen, A.

English

IUScholarWorks

FURTHER STUDIES OF UNUSUAL FISSION MASS DISTRIBUTIONS USING 190 M e V  PROTONS 
F.D. Becchet t i ,  P. L i s t e r ,  and J. Janecke 
Unive r s i ty  of Michigan, Ann Arbor, Michigan 48109 
A. Nadasen 
l ln ive r s i ty  of Michigan, Dearborn, Michigan 48128 
K. Hicks 
Un ive r s i ty  of Colorado, Boulder, Colorado 80309 
J. ~rown+, K. Kwiatkowski, and H. Karwowskis 
Indiana l h i v e r s i t y  Cyclotron F a c i l i t y ,  Bloomington, Indiana 47405 
We have continued our s tudy of symmetric and Two new elements were s tud ied  (Nd and Dy), 
asymmetric f i s s i o n  of intermediate-mass nuc le i  us ing toge the r  with new t a r g e t s  of masses (Ce and Er) s tud ied  
190 MeV protons.  A three-detector  AE-E counter  previously  without the  AE-E d e t e c t 0 r . l  A LIE-E 
t e l e scope ,  c o n s i s t i n g  of a commorranode AE i o n  chamber spectrum f o r  Ce is  shown i n  Fig. 1. This  appears  t o  be 
("12.6 t o r r  i sobutane)  and th ree  l a r g e  a rea ,  300 m2, c o n s i s t e n t  wi th  the  unusual ly  symmetric f i s s i o n  mass 
Si(SB) d e t e c t o r s  ( i n  gas)  i n  coincidence with a three- d i s t r i b u t i o n  140 + 50(Z=20) + 80(Z-35) + ... deduced 
d e t e c t o r  Si(SB) a r r a y  was used t c )  provide approximate previously .  Likewise mass (and Z) d i s t r i b u t i o n s  f o r  
fragment Z i d e n t i f i c a t i o n  a s  well. a s  fragment ene rg ie s  o t h e r  t a r g e t s  near A = 140 (Nd and Dy) e x h i b i t  broad 
(TKE). This ,  t oge the r  with fragment TOF r e l a t i v e  t o  and/or double-peaked mass d i s t r i b u t i o n s  (Fig.  2). This 
t h e  beam r.f . (At-0.5 ns) provides Z and A 
i d e n t i f i c a t i o n .  The TKE i s  used t o  sepa ra t e  
contaminants.  
i s  i n d i c a t i v e  of a t rend towards broad, asymmetric 
f i s s i o n  a s  A + 100 which is  p red ic t ed  by the  l i q u i d  
drop model (BG po in t ) .  Recent s t u d i e s 4  a t  Ep=l GeV 
a l s o  i n d i c a t e  such behavior (Fig.  3). 
v- We have a l s o  obta ined angular  c o r r e l a t i o n s  (us ing 
t h e  coincidence da ta )  and angular  d i s t r i b u t i o n s  (us ing 
Z singles d a t a  and p l a s t i c  t r a c k  d e t e c t o r s ) .  Fu r the r  
Figure  1. Ion-chamber - Si(SB) d e t e c t o r  spectrum of 
AE-E f o r  co inc iden t  ptCe f i s s i o n  fragments (ED = 190 
30 - 
- 
- {O 
I I I 
MeV) gated on the  f i s s i o n  peak i n  TKE. The c d c u l a t e d  
contours  f o r  var ious  fragment Z va lues  a r e  indicated.  
s t u d i e s  using a 200 MeV 3 ~ e  beam have been approved, 
which w i l l  permit i n v e s t i g a t i o n  of the  r eg ion  A < 140, 
y e t  s t i l l  wi th  r e l a t i v e l y  low angular  momentum and mass 
t r a n s f e r .  
+present  address  : Physics  Department, P r ince ton  
Unive r s i ty ,  Pr inceton,  N J  08544 
1) F.D. Becchet t i  e t  a l . ,  Phys. Rev. C 28, 276 
( 1  983). 
20 60 100 b ~ r e s e n t  address  : Physics Deyar tuen t ,  Un ive r s i ty  of 
ENERGY (MeV) North Carol ina ,  Chapel H i l l ,  NC 27514 
2) P. L i s t e r  e t  a l . ,  Proc. 4 t h  I n t l .  Conf. on 
C lus t e r ing  Aspects of Nuclear Reactions and Nuclear 
S t ruc tu re .  Chester ,  GB, J u l y  1984. 
3) G. Anderson e t  a l . ,  Z. Phys. A293, 241 (1979). 
4 )  L.N. Andronenko e t  a l . ,  2. Phys. A318, 97 (1984). 
a , V  Ep = 1.0GeV 
o Ep = 600 MeV 
m ,  Ep = 1 9 0  MeV 
0 
0 
t 
BG POINT 
F i g u r e  3. F i s s i o n  mass widths  (deduced from 
M ~ / M ~ + M ~ )  = E2/(E1+E2) o r  d i r e c t l y  measured w i th  TOF) 
f o r  proton-induced f i s s i o n  (1  GeV: Ref. 4; 600 MeV: 
Ref. 3; 190 MeV: t h i s  work and Ref. 1). 
F igu re  2. I n f e r r e d  mass s p e c t r a  
[M1/(M1+M2) = E2/(E1+E2)] f o r  c o i n c i d e n t  f i s s i o n  
f ragments  [(01-02) = 168'1 ga t ed  on t h e  peak i n  t h e  TKE 
spec t rum corresponding  t o  b ina ry  f i s s i o n  f o r  t he  masses 
i n d i c a t e d  (TKE = 0.107 z2/~lI3 + 22.2 MeV). 


Further Studies of Unusual Fission Mass Distributions using 190 MeV Protons

https://scholarworks.iu.edu/dspace/bitstream/2022/1110/1/iucf_1984_98-99.pdf

Further Studies of Unusual Fission Mass Distributions using 190 MeV Protons

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