Supported by the National Science Foundation and Indiana Universit

Bainum, D.

Foster, C.C.

Goodman, C.D.

Lind, D.A.

Masterson, T.G.

Rapaport, J.

Raymond, R.S.

Schery, S.D.

Sugarbaker, E.

Zafiratos, C.D.

English

IUScholarWorks

FWHM. I I I I I 
Preliminary d a t a  a t  Ep= 160 MeV appears t o  indi -  
IAS 
c a t e  t h a t  t he  r a t i o  of sp in - f l i p  t o  non-spin-flip 
s t r eng th  is l a r g e r  than a t  120 MeV, but  t he  r e so lu t ion  
is s u f f i c i e n t l y  worse t h a t  t he  i n t e r p r e t a t i o n  is l e s s  1000 - 
c l e a r  c u t .  
1 )  R.R. Doering, A. Galonsky, D.M. Pa t te rson ,  and 
G.F. Bertsch,  Phys. Rev. L e t t .  35, 1691 (1975). 
2) C.D. Goodman, Te l lu r ide  Conference, March 29-31, 
1979. 
100 110 120 
F" ( M e V )  
F i v e  2. Neutron spectra incZuding f i t s  t o  peak 
shapes for the 03 23 (p,n) reactions a t  120 MeV 
proton bombarding energy. 
NEUTRON MATTER DISTRIBUTIONS FROM QUASI-ELASTIC (p,n) REACTIONS 
D. Bainum 
Emporia State  University, Emporia, Kansas 66801 
C.C.  Fos ter  and C.D. Goodman 
Indiana University CycZotron Faci l i ty ,  BZoomington, Indiana 47405 
D.A. Lind, C.D. Za f i r a to s ,  R.S. Raymond, T.G. Masterson, and E. Sugarbaker 
university of Co Zorado, Boulder, Co lorado 80309 
J. Rapaport 
Ohio University, Athens, Ohio 45701 
S.D. Schery 
New Mexico A&M University, Socorro, New Mexico 87801 
Runs made e a r l y  i n  t h e  year on Z r ,  Sn and Pb t o  r e n t l y  of i n t e r e s t  a r e  gound s t a t e  IAS t r a n s i t i o n  
look a t  (p,n) neutron spec t r a  a t  angles much l a r g e r  s t r eng ths  and t h e  g i a n t  resonance s t r eng ths ,  For both 
than 15' indica ted  t h a t  t h e  genera l  background, mainly problems improved signal-to-background was needed. 
cosmic ray  neutron and muon events,  was so  l a r g e  t h a t  it I n  t he  pas t  year very s u b s t a n t i a l  improvements i n  
was not  pos s ib l e  t o  t ake  angular  d i s t r i b u t i o n s  on l a r g e  t h e  chopped beam cu r ren t  a t  t h e  TOF t a r g e t s  has occurred. 
A t a r g e t s  a t  angles beyond 20'. The two f e a t u r e s  cur- The o the r  improvement made was t h e  i n s t a l l a t i o n  of l a r g e  
ve to  s c i n t i l l a t i o n  paddles t o  e l iminate  t h e  charged 
component of cosmic rays .  Two paddles were used; a  
v e r t i c a l  u n i t  was placed i n  f r o n t  and a ho r i zon ta l  u n i t  
on top-of two neutron de t ec to r s .  Thus charged p a r t i c l e s  
generated by neutron i n t e r a c t i o n s  i n  t h e  a i r  ahead of t h e  
de t ec to r s  were a l s o  el iminated.  With t hese  u n i t s ,  back- 
ground when no neutron beam was present  was reduced by 
a f a c t o r  of about 7 f o r  d e t e c t o r s  opera t ing  a t  a  thres-  
hold of 15 MeV f o r  neutrons.  F i g . l  shows t h e  neutron 
time-of-flight spectrum f o r  12%n a t  20.2 deg and 79.3 
MeV proton energy. The threshold  was no t  q u i t e  high 
enough t o  e l imina t e  neutrons from t h e  preceding beam 
bur s t .  There is t o  t h e  l e f t  of t h e  prominent IAS peak 
evidence f o r  t he  g i an t  resonance which is very prominent 
i n  Sn a t  120 MeV, a s  we l l  a s  i n  a l l  Z r  t a r g e t s  a t  t h i s  
energy. 
A s  a  r e s u l t  of e a r l i e r  experience wi th  Sn t a r g e t s  
a t  120 MeV, i t  was decided t o  s e t  t h e  proton energy a t  
80 MeV and use a f l i g h t  d i s t ance  of 46.3 meters wi th  
optimum veto  sh i e ld ing  t o  i n su re  t h a t  angular  d i s t r i -  
but ions  could be generated out  t o  angles  where s igni -  
f i c a n t  ana lys i s  becomes poss ib le .  Two experiments were 
c a r r i e d  out  together .  A Michigan S t a t e  Universi ty group 
took da t a  on B 9 2 9  9 4 ~ r  f o r  t h e  g i a n t  resonance 
phenomena and is r epo r t i ng  t h e i r  r e s u l t s  separa te ly .  
This group confined a n a l y s i s  t o  t h e  IAS s t a t e s  i n  
9 0 , 9 2 9 9 4 ~ r  and 112,116,124~n.  In t h e  time ava i l ab l e ,  
runs from oOto 24' l a b  angle  range were recorded. The 
beam was pulsed wi th  one pu l se  i n  f i v e  R.F. cyc l e s  
accepted and y ie lded  up t o  350 nA a t  t h e  t a r g e t .  A 
proton monitor de t ec to r  cons i s t i ng  of  a  f a s t  passing 
counter  ( P i l o t  U s c i n t i l l a t o r  mounted on a C31024 RCA 
phototube) generated t i m e  re ference  pulses  f o r  t h e  time 
compensation c i r c u i t r y  t o  accept .  Optimum time re-  
s o l u t i o n  was 1 n s  bu t  timing was q u i t e  s t a b l e .  This 
Figure 2. Angular distribution data taken for the IAS 
state  with targets of 92,94~r  and 112,116, 12'+sn by 
the fp,n) reaction a t  an energy of 79.2 MeV. Note that 
points for Zr isotopes have been displaced relat ive t o  
one another. 
r e so lu t ion  was not  de t r imenta l  f o r  t h e  da t a  t h a t  
t he se  experiments provided. It was moreover, consis-  
t e n t  wi th  t h e  beam cu r ren t  pulse  a s  seen by t h e  proton 
monitor, t h e  energy l o s s  i n  t h e  t a r g e t s  and t h e  depth 
of t h e  neutron de t ec to r .  
same o rd ina t e  s c a l e  and show t h e  a c t u a l  d i f f e r ences  bet-  
ween i so topes .  I n  t h e  case  of Z r  t he  curves f o r  9 2 ~ r  
and 9 4 ~ r  have been d isp laced  upwards by 1.1 and 1.2, 
respect ive ly .  The d i f f e r ences  a r e  i n  t h e  v i c i n i t y  of t h e  
f i r s t  maximum a t  18' and a r e  genera l ly  much smal ler  than 
f o r  t he  Sn. 
Absolute normalizat ion was done using t h e  7 ~ i ( p  ,n) 7 ~ e  
t o t a l  c ros s  s ec t ion  and angular  d i s t r i b u t i o n  measure- 
ments. The method used is described b r i e f l y  by Ward 
e t  a1  .' i n  t he  1978 IUCF Annual Report. The y i e l d  
i n  t h e  (p,n) r eac t ion  on a 7 ~ i  t a r g e t  of known a r e a l  
dens i ty  was measured a t  0'. The absolu te  normalizat ion 
is  5 5  percent .  For t h e  purposes of t h e  model a n a l y s i s  
F i  w e  . Neutron time-of-fl ight spectrum for the 
%fnl 1 2 4 ~ ~  lreaction at 79 2 ~~v 20.2 deg. llhe t h i s  va lue  is not  of importance s ince  only r e l a t i v e  
figure contains 3000 chmneZs wi th  200 counts/channeZ 
fuZZ scale. changes between t h e  i so topes  w i l l  be used. 
The a n a l y s i s  r equ i r e s  t h e  fo ld ing  model code 
The angular  d i s t r i b u t i o n  d a t a  a r e  presented f o r  each developed by ~ c h e r ~ . ~  A s  soon a s  i t  i s  adapted t o  
i so tope  i n  a sequence i n  Fig. 2. The s t a t i s t i c a l  e r r o r  Universi ty of Colorado computing f a c i l i t i e s ,  searches 
on each da t a  poin t  is shown. Areal d e n s i t i e s  of t h e  Z r  f o r  t h e  bes t  f i t  parameters w i l l  be made. Predic t ions  
t a r g e t s  were determined by weighing. The Sn t a r g e t s  were f o r  t h e  angular  d i s t r i b u t i o n s  t o  l a r g e r  angles  w i l l  be 
compared by measuring the  e l a s t i c  s c a t t e r i n g  of protons made t o  plan f o r  f u t u r e  runs on t h i s  experiment. Such 
a t  8' i n  t he  l a b  frame and ca l cu l a t i ng  t h e  apparent  re -  r e s u l t s  a r e  not  y e t  ava i l ab l e .  
l a t i v e  d e n s i t i e s  using a g lobal  o p t i c a l  model t o  p red i c t  1)  T.E. Ward, C.A. Goulding, M.B. Greenfield,  C.C. 
Foster ,  J. Rapaport, C.D. Za f i r a to s ,  S.D. Schery 
r e l a t i v e  angular  d i s t r i b u t i o n s .  There was a l s o  some and C.D. Goodman, IUCF Annual Report, 54 (1978). 
Also C.C. Fos ter  e t  a l . ,  Bul l .  Am. Phys. Soc. 24, 
uncer ta in ty  i n  t he  p rec i se  r ep roduc ib i l i t y  of measurements. 828 (1979). 
These unce r t a in t i e s  a r e  indica ted  by e r r o r  ba r s  on t h e  2) S.D. Schery i n  "The (p,n) Reaction and t h e  Nucleon- 
Nucleon Force" Proceedings, Te l lu r ide ,  CO (1979), 
0' po in t  f o r  each i so tope .  The curves f o r  Sn a r e  on t h e  t o  be published. 


Neutron Matter Distributions from Quasi-Elastic (p,n) Reactions

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Neutron Matter Distributions from Quasi-Elastic (p,n) Reactions

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