Supported by the National Science Foundation and Indiana Universit

Bacher, A.D.

Blatt, S.L.

Boyd, R.N.

Donoghue, T.R.

Foster, C.C.

Hausman, H.J.

Kovash, M.A.

English

IUScholarWorks

RADIATIVE PROTON CAPTURE 
RADIATIVE PROTON CAPTURE: RECENT RESULTS 
S.L. B l a t t ,  M.A. Kovash, R.N. Boyd, T.R. Donoghue, and H.J. Hausman 
The Ohio State  University, CoZwnbus, Ohio 4321 0 
A.D. Bacher and C.C. F o s t e r  
Indiana University CycZotron Faci Zity , BZoomington, Indiana 4 7405 
The f i r s t  s t u d i e s  of (p ,y )  r e a c t i o n s  i n  t h e  40-100 c i t e d  s t a t e s .  The measurements which f i r s t  demon- 
MeV range were undertaken by our  group l e s s  than  two s t r a t e d  t h i s  e f f e c t  have been publ i shed  i n  P h y s i c a l  
y e a r s  ago. Although t h e  i n i t i a l  mot iva t ions  f o r  t h e s e  Review ~ e t t e r s .  ' More r e c e n t l y ,  t h e  u n f o l d i n g  e v i -  
s t u d i e s  were cen te red  on ground-state  c a p t u r e  phe- dence h a s  been presen ted  a t  a  number of conferences  
nomena, t h e  r e s u l t s  of our  e a r l y  experiments  have and workshops. 2-4 At l e a s t  t h r e e  t h e o r e t i c a l  works 5-7 
d i r e c t e d  o u r  e f f o r t s  toward an  unexpected a s p e c t  of have been prompted by our  r e s u l t s .  
t h e s e  r e a c t i o n s :  s t r o n g  c a p t u r e s  t o  high-lying ex- I n  t h e s e  s t u d i e s ,  we have concent ra ted  on t h e  
r e a c t i o n s  1 1 ~ ( p , y ) 1 2 ~  and 1 2 ~ ( p , y ) 1 3 ~ .  However, 
r 
z 
3 
0 
U 4 0 0 9  
200 - 
28.7 MeV, 75' 
50 I00 
CHANNEL NUMBER 
o t h e r  r e a c t i o n s  have a l s o  been s t u d i e d ,  i n  a  l e s s  
d e t a i l e d  way, t o  g a i n  some unders tand ing  of t h e  
s y s t e m a t i c s  of t h e  f i n a l  s t a t e s 3  observed i n  t h e  
p ro ton  c a p t u r e  r e a c t i o n  a t  e n e r g i e s  above t h o s e  ob- 
t a i n a b l e  w i t h  tandem Van de  G r a a f f s .  The p i c t u r e  
which emerges is  a s imple  one: t h e  f i n a l  s t a t e s  
a r e  ones which have a  s t r u c t u r e  which looks  l i k e  t h e  
undis tu rbed  t a r g e t  nuc leus  coupled t o  a  s i n g l e  p ro ton  
one major s h e l l  above t h e  h i g h e s t  s h e l l  occupied by 
pro tons  i n  t h e  t a r g e t  nuc leus .  Thus, f o r  example, 
i n  I B ( ~ ,  y ) 12c, t h e  s t a t e s  most s t r o n g l y  popula ted  
a r e  t h o s e  w i t h  one p h o l e  and an  s-d s h e l l  p r o t o n  312 
( s e e  F ig .  1 ) .  I n  1 2 ~ ( p ,  y) 3 ~ ,  s i n g l e - p a r t i c l e  s-d 
s h e l l  s t a t e s  predominate; and i n  1 2 ~ ( p ,  y ) 3 ~ ,  s t u d i e d  
elsewhere,8 t h e  primary f i n a l  s t a t e s  a r e  of p  1 312  
(s-d) n a t u r e .  
The energy dependence of t h e  s t r o n g e s t  c a p t u r e  
t r a n s i t  ions  i n  IB ( p ,  y)  12C shows a resonance- l ike  
Figure I .  Gamma-ray spectrwn from B (p,  y) 2~ a t  behavior ,  peaking n e a r  Ep=30 MeV ( s e e  F ig .  2).  Since  
Ep=28. 7 MeV, OLAB=75O. Structure i n  the y19 complex 
corresponds t o  capture t o  known negat i7~-pari ty  t h e  f i n a l  s t a t e s  upon which t h i s  resonance is  b u i l t  a r e  
s tates ,  which may be iden t i f i ed  as (p;!2, s -d l )  
configurations. components of  t h e  ground-state  g i a n t  resonances ,  and 
4000r "B(D.~ lmc to even higher excitations in the final nuclei. A I 8L. ' 60. simple analysis suggests that transitions to the second 
tion, and of the nuclear structure effects it reveals. 
. 
3000- 
Fipzlre 2. Excitation functions for proton capture 
i n t o  12C,  a t  0 =60 . Calculations of Londergan 
and Tsai are sh% as solid l ines; the dashed l ines  
merely join the data points. 
t
,% harmonic resonance region, perhaps from a still-higher 
' \ $ \ , , / E x P X * P ~ ~ H E M  resonance, may explain the observations. A further 
r- extension of the experimental information is also being 
1) M.A. Kovash, S.L. Blatt, R.N. Boyd, T.R. Donoghue, 
H.J. Hausman, and A.D. Bacher, Phys. Rev. Lett. 42, 
700 (1979). 
pursued through the measurement of analyzing powers 
with the polarized proton beam. Preliminary results 
from our first run, at 28.5 MeV, show substantial ana- 
lyzing powers. Further, the l l ~ ( ~ , ~ )  12c transition to 
-1 1 the d5,2) states has an analyzing power strik- 
ingly similar to the transition to the single-particle 
dgI2 state in 12~(p,y)13~. 
Work is continuing in the effort to develop as 
complete an understanding as possible of the (p,y) reac- 
2) S.L. Blatt, M.A. Kovash, H.J. Hausman, T.R. Donoghue, 
R.N. Boyd, A.D. Bacher, and C.C. Foster, Proc. Giant 
Multipole Topical Conf., Oak Ridge, Tenn. (1979). 
since the integrated cross section exhausts over 15% 
3) S . L .  Blatt, M.A. Kovash, T.R. Donoghue, H.J. 
of the dipole sum-rule value, the phenomenon can be Hausman, and A.D. Bacher, Bull. Am. Phys. Soc. 
24, 843 (1979). 
-
described as a "second-harmonic giant resonance." The 
4) S.L. Blatt, Proc. Workshop on Nucl. Structure 
theory of Tsai and ~ o n d e r ~ a n , ~  which is essentially a with Intermed. Enerpy Probes, Los Alamos, N.M. 
(1980). 
direct-capture picture, does not reproduce the observed 
5) L.G. Arnold, Phys. Rev. Lett. 42, 1253 (1979). 
energy dependence. 
6) S.-F. Tsai and J.T. Londergan, Phys. Rev. Lett. 
Additional data are being collected to extend our - 43, 576 (1979). 
understanding of these effects. Detailed spectra at 7) D. Halderson and R.J. Philpott, to be published 
(1980). 
energies 2 50 MeV show much strength at gamma-ray ener- 
8) P. Paul, H.S. Kuan, and F.K. Warburton, Nucl. 
gies below the transitions to the ground-state giant Phys. A254, 1 (1975); S .  Manglos, H.R. Weller, 
N.R. Roberson, D.R. Tilley, S . A .  Wender, and 
resonance region; i.e., we may be seeing transitions S . L .  Blatt, APS Washington Meeting (1980). 


Radiative Proton Capture: Recent Results

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Radiative Proton Capture: Recent Results

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