Supported by the National Science Foundation and Indiana Universit

Bent, R.D.

Green, M.C.

Pile, P.H.

Sjoreen, T.P.

Soga, F.

English

IUScholarWorks

with  the  experimental  r e s u l t s .  
1 )  P.H. P i l e  and R.E. Pollock,  Nucl. Instrum. Methods 
165, 209 (1979). 
-
2) P.H. P i l e ,  R.D. Bent, R.E. Pol lock ,  P.T. Debevec, 
R.E. Marrs, M . C .  Green, T.P. Sjoreen and F. Soga, 
Phys. Rev. L e t t .  42, 1461 (1979). 
3) R.E. Pollock,  P.H. P i l e ,  H.O.  Meyer and G.T. Emery, 
Bul l .  Am. Phys. Soc. 24, 614 (1979). 
4) E.G. Auld, A. Haynes, R.R. Johnson, G .  Jones ,  T. 
Masterson, E.L. Mathie, D. O t t ewe l l ,  P. Walden, and 
B. T a t i s c h e f f ,  Phys. Rev. L e t t .  41, 462 (1978). 
5 )  M.C. Tsangarides,  t h e s i s ,  Indiana Un ive r s i t y ,  1979, 
IUCF I n t e r n a l  Report #79-4. 
6) W. Gibbs, I nv i t ed  Paper ,  LAMPF Workshop on Nuclear 
S t r u c t u r e  wi th  In te rmedia te  Energy Probes,  Los 
Alamos, 1980 (unpublished).  
HIGH RESOLUTION STUDIES OF THE (p,n+) REACTION ON l p  SHELL NUCLEI AT Ep=200 MeV 
F. Soga, R.D. Bent, P.H. P i l e ,  T.P. S joreen ,  and M.C. Green 
Indiana univers i ty  Cyclotron Faci l i ty ,  Bloomington, Indiana 47405 
It was shown by Dahlgren e t  a l .  i n  one of t h e  t i o n  and have t h e  l a r g e s t  s i n g l e - p a r t i c l e  spec t ro scop i c  
e a r l y  Uppsala papers  on nuc l ea r  p ion  product ion  near  f a c t o r s .  The 2.14(1/2-) s t a t e ,  which is  forb idden  by 
+ 
t h r e sho ld  t h a t  t h e  1 2 ~ ( p ,  IT ) 3~ r e a c t i o n  produces f i n a l  
s t a t e s  of complicated s t r u c t u r e  j u s t  a s  s t r on g ly  a s  
s t a t e s  t h a t  can be  reached by t h e  d i r e c t  t r a n s f e r  of a  
neutron.  This  is  i l l u s t r a t e d  by t h e  upper spectrum 
shown i n  Fig. 1, which was taken  r e c e n t l y  a t  IUCF wi th  
an  o v e r a l l  energy r e s o l u t i o n  of 170 keV. The f a c t  t h a t  
t h e  1plI2, 2slI2 and ldgI2  s i n g l e - p a r t i c l e  s t a t e s  a t  
0.0, 3.09 and 3.85 MeV, r e spec t i ve ly ,  and t h e  two 
pa r t i c l e -one  h o l e  s t a t e s  a t  3.68, 6.86 and 9.50 MeV a r e  
populated about  equa l ly  provided e a r l y  evidence i n  sup- 
p o r t  of a  two-nucleon2 o r  m u l t i s t e p  r e a c t i o n  mechanism. 
+ Recent h igh  r e s o u l t i o n  s t u d i e s  of t h e  ( p , ~  ) re -  
a c t i o n  on o the r  t a r g e t s  i n  t h e  p-she l l  i n d i c a t e  t h a t  
s t r ong  product ion  of core-exc i ted  s t a t e s  may be  t h e  
except ion  r a t h e r  than  t h e  r u l e .  F igure  2 ( top)  shows a 
+ 
OB (p,  IT ) l~ spectrum taken  a t  IUCF wi th  an  o v e r a l l  
energy r e s o l u t i o n  of 210 keV. The f i v e  low-lying s t a t e s  
of odd-pari ty i n  1 1 ~  a r e  be l i eved  t o  a r i s e  mainly from 
con f igu ra t i ons  comprised of pjI2 and pIl2 nucleons and 
a r e  w e l l  descr ibed  by t h e  s h e l l  model based on t h e  i n t e r -  
mediate  coupling ~ c h e m e . ~  The s t a t e s  a t  0.00(3/2-) and Excitation Energy (MeV) 
+ 4.44(5/2-) MeV which a r e  s t r o n g l y  exc i t ed  i n  t h e  ( p , ~  ) Fi ure 1 Pion energy spectra from the  reactions 
3C and 3 ~ ( p ,  a+) 14c a t  T =200 MeV and 
r e a c t i o n  a l s o  a r e  populated s t r ong ly  i n  t h e  (d,p) reac-  OIT(labl = 25'. P 
r e a c t i o n  b u t  t o  a  l e s s e r  degree.  
Because of t h e  l a r g e  momentum t r a n s f e r  i n  t h e  
+ (p,n ) r e a c t i o n ,  t r a n s i t i o n s  t o  s t a t e s  of h igh  angula r  
momentum a r e  expected t o  be  p r e f e r r e d .  This  may account  
f o r  some of t h e  enhancements seen  i n  t h e  O B ( ~ ,  n+) 'B 
r e a c t i o n  b u t  cannot  e x p l a i n  t h e  r e l a t i v e  i n t e n s i t i e s  of 
t r a n s i t i o n s  t o  t h e  two 312- s t a t e s  a t  0 .0 and 5.02 MeV 
n o r  t h e  s t r o n g  suppress ion  of t r a n s i t i o n s  t o  t h e  s t a t e s  
a t  2.14, 7.3, 8 .0 and 8.57 MeV. 
+ A s i m i l a r  s e l e c t i v i t y  is  e x h i b i t e d  by t h e  I ~ B ( ~ , R  ) 
1 2 ~  r e a c t i o n  (F ig .  2, bottom). I n  t h i s  c a s e ,  s t a t e s  
a t  0.0 ( l f ) ,  0.95 (2+), 1.67 (2-) and 2.62 (I-) MeV, 
which can be  formed by coupling a  p  o r  2s  neu t ron  112 112 
t o  t h e  1~ ground s t a t e ,  a r e  populated s t r o n g l y ,  whereas 
+ 
t h e  2.72 MeV ( 0  ) s t a t e ,  which r e q u i r e s  recoupl ing  of 
c o r e  nucleons t o g e t h e r  w i t h  t h e  t r a n s f e r  of a  neu t ron ,  
i s  populated weakly. A p r e f e r e n c e  f o r  s i n g l e - p a r t i c l e  
+ f i n a l  s t a t e s  is a l s o  seen  i n  t h e  1 3 ~ ( p , ~  ) 14c r e a c t i o n  
Excitation Energy (MeV) (F ig .  1, bottom); f o r  example, t h e  0  + s i n g l e - p a r t i c l e  
+ 
Fi ure 2 P<on energy spectra from the reactions ground s t a t e  i s  e x c i t e d  s t r o n g l y  compared t o  t h e  0  
*1 lB and l ~ l p ,  n+) l2I3 a t  T =200 MeV and 
e , ( ~ a b ) = 2 5 ~ .  P  core-exci ted s t a t e  a t  6.59 MeV. 
+ I n  s h o r t ,  f o r  t h e  ( p , ~  ) r e a c t i o n  on 1°B, l lB and 
a  one-step mechanism, and t h e  5.02(3/2-) s t a t e ,  which is 
3~ t a r g e t s  a t  200 MeV bombarding energy,  f i n a l  s t a t e s  p r e d i c t e d  by t h e  intermediate-coupling model t o  have 
little overlap with t h e  1  oB ground state, are both popu- that can be reached the transfer of a neutron 
+ l a t e d  weakly i n  t h e  ( p , ~  ) and (d,p)  r e a c t i o n s .  The tend t o  be  favored compared t o  s t a t e s  of more complicated 
three even parity states at 7.30, 8 - 0 0  and 8-57  MeV a r e  structure* This is suggestive of a one-step reaction 
c h a r a c t e r i z e d  by weak (d,p)  i n t e n s i t i e s  s u g g e s t i v e  of mechanism. A q u i t e  d i f f e r e n t  behavior  i s  observed f o r  
+ 
h i g h l y  mixed c o n f i g u r a t i o n s .  These s t a t e s  a r e  a l s o  pop- t h e  12c(p,  T ) '% r e a c t i o n ,  which popula tes  s i n g l e - p a r t i c l e  
+ 
u l a t e d  weakly i n  t h e  ( p , ~  ) r e a c t i o n .  The two s t a t e s  and 2p-lh f i n a l  s t a t e s  about  e q u a l l y ,  demonstrat ing 
of even p a r i t y  n e a r  9  MeV have very  l a r g e  (d,p)  s t r i p p i n g  t h e  multi-nucleon a s p e c t  of t h e  p roduc t ion  process  
ampli tudes c h a r a c t e r i s t i c  of d i r e c t  neu t ron  c a p t u r e  i n t o  f o r  t h i s  p a r t i c u l a r  c a s e  (which seems t o  be  an  ex- 
t h e  2s  o r  I d  s h e l l  wi thout  a p p r e c i a b l e  e x c i t a t i o n  of t h e  c e p t i o n  i n  t h e  l p - s h e l l ) . .  
+ 
~ O B  c o r e .  T r a n s i t i o n s  t o  t h e s e  s t a t e s ,  a s  w e l l  a s  t h e  The i n t e r p r e t a t i o n  of ( p , ~  ) d a t a  i s  d i f f i c u l t  
6.7 MeV double t  s t a t e  (presumably mainly t h e  6.74(7/2-) because of  t h e  unknown way i n  which t h e  r e a c t i o n  
+ 
s i n g l e - p a r t i c l e  s t a t e ) ,  a r e  enhanced i n  t h e  ( p , ~  ) dynamics and n u c l e a r  s t r u c t u r e  e f f e c t s  a r e  i n t e r -  
r e l a t e d ,  and a l s o  because t h e r e  appear t o  be s eve ra l  e f f e c t s  t o  i s o l a t e  d i f f e r e n t  a spec t s  of t h e  r eac t ion  
r eac t  ion  mechanisms with poss ib ly  d i f f e r e n t  energy- process. 
and A-dependences. The high r e so lu t ion  spec t r a  shown 1 )  S. Dahlgren, P. G r a f s t r h ,  B. HEistad, and 2. Asberg, 
Nucl. Phys. A211, 243 (1973). 
here  i nd i ca t e  t h a t  t h e  dominant r eac t ion  mechanism 
2) Z.  Grossman, F. Lenz, and M.P. Locher, Ann. of Phys. 
is deterrhined t o  a c e r t a i n  ex t en t  by t h e  nuclear  84, 348 (1974). 
-
s t r u c t u r e  changes t h a t  occur during t h e  r eac t ion ,  and 3) G.A. Mi l l e r ,  Nucl. Phys. A224, 269 (1974). 
t h a t  i t  may be poss ib l e  t o  use nuclear  s t r u c t u r e  4) S. Cohen and D. Kurath, Nucl. Phys. A101, 1 (1967). 
ENERGY DEPENDENCE OF THE 12c (p, n+) 3 ~ *  REACTION TO 2p-lh FINAL STATES 
F. Soga, R.D. Bent, M.C.  Green, W.W. Jacobs, P.H. P i l e ,  T.P. Sjoreen,  and T.E. Ward 
Indiana University CycZotron Facility,  BZoomington, Indiana 4 7405 
A.G. Drentje 
~ern fy s i s ch  Versne Z Zer Inst i tuut ,  Groningen, The   ether Zands 
+ * The r eac t ions  1 2 ~ ( p , ~  )13c  leading  t o  s p e c i f i c  
f i n a l  s t a t e s  have been s tudied  wi th  proton beams i n  t h e  
energy range 166 t o  200 MeV. The aim of t h i s  work is 
+ 
t o  shed l i g h t  on t h e  mechanism of t h e  (p,n ) r eac t ion  
by comparing t h e  energy dependence of t r a n s i t i o n s  t o  
2p-lh s t a t e s  a t  EX = 3.68(3/2-), 6.86(5/2+) and 9.50 
+ (912 ) MeV wi th  t h a t  of t r a n s i t i o n s  t o  s i n g l e - p a r t i c l e  
s t a t e s  a t  0.0(1/2-) , 3.09(1/2+) and 3.85(5/2+) MeV. 
Angular d i s t r i b u t i o n s  a t  s eve ra l  energies  have been 
measured using t h e  QDDM and DC pion spectrographs.  The 
close-lying s t a t e s  a t  3.68 and 3.85 MeV were c leanly  
resolved wi th  t h e  QDDM spectrograph ( see  Fig. l ) ,  and 
sepa ra t e  angular  d i s t r i b u t i o n s  f o r  t he se  s t a t e s  were 
obtained f o r  t h e  f i r s t  time. The measured angular  d i s -  
t r i b u t i o n s  of t h e  d i f f e r e n t i a l  c ros s  s ec t ions  a r e  shown 
i n  Fig. 2 together  wi th  185 MeV Uppsala da t a .  
A comparison of t h e  angular  d i s t r i b u t i o n s  f o r  t ran-  
s i t i o n s  t o  t h e  two 512' s t a t e s  ( t h e  s ing l e -pa r t i c l e  
( ldgI2) s t a t e  a t  3.85 MeV and t h e  core-excited 
( ldgI2  + 2slI2 B 1p3 /24  1plI2) s t a t e  a t  6.86 MeV) 
i n d i c a t e s  t h a t ,  though t h e  shapes of t h e  angular  d i s -  
t r i b u t i o n s  a r e  s imi l a r  except f o r  a  displacement i n  
pos i t i on  of t h e  minimum, t h e  magnitudes and energy 
dependences of t h e  t o t a l  c r o s s  s ec t ions  a r e  q u i t e  
d i f f e r e n t  (Fig.  3 ) .  The main component of t h e  3.68 MeV 
12 13 C(P , *+ )  c 
Ep ~174.4 MeV 
8, = 25O (lob.) 
FWHM 
= 63 keV 
CHANNEL No. 
+ 
Figure 1. The spectrum fo r  doublet state i n  12cfp, a 1 3~ 
reaction obtained with the QDDM magnetic spectrograph. 


High Resolution Studies of the (p,Pi+) Reaction on 1p Shell Nuclei at E_p=200 MeV

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High Resolution Studies of the (p,Pi+) Reaction on 1p Shell Nuclei at E_p=200 MeV

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