This work was supported by National Science Foundation Grant PHY 75-00289 and Indiana Universit

Devins, D.W.

Friesel, D.L.

Henderson, R.S.

Jones, W.P.

Officer, V.C.

Shute, G.G.

Spicer, B.M.

Svalbe, I.D.

English

IUScholarWorks

STUDIES OF KNOCK-OUT REACTIONS 
D.W. Devins, D.L. F r i e s e l ,  W.P. Jones, B.M. Spicer*, V.C. Officer*,  G.G. Shute*, I .D.  Svalbe*, and 
R.S. Henderson* 
A d e t a i l e d  understanding of nuclear  spectroscopy 
through nuclear  r eac t ions  a t  IUCF energies  is no t  
pos s ib l e  without a de t a i l ed  understanding of t h e  
mechanisms of t h e  reac t ions .  Many f a c t o r s  con t r i -  
1 ' 1 ' 1 8 1 1  
"c(P,~P)"B 4 Ground Stare 
angular carr*lation 4 2.124 MeV 
bute  t o  t he  d i f f i c u l t i e s  one has  i n  obta in ing  such 
an understanding. There has always been a ques- 
1 
t i o n  of t h e  importance of mult iple-step processes 
i n  nuclear  reac t ions ,  and more r ecen t ly  t h e  exis -  
1 )  tence of two-step mechanisms has been e s t ab l i shed .  
30 40 50 60 
The ex t en t  t o  which two-step processes a r e  irn- Lab Angle (dog) 
por t an t  a t  IUCF energies  is e s s e n t i a l  t o  e s t ab l i sh :  Figure 2. 
i f  they a r e  important, they w i l l  complicate re-  s tanding  of two-step processes a s  exemplified by the  
ac t ion  formulat ions and make r e l i a b l e  spectro-  ( ~ ~ 2 ~ )  reac t ion .  
scopic  information ex t r ac t ion  d i f f i c u l t ;  a t  t he  Our 100 MeV 12c (p, 2p)11~ runs a t  t h e  equal  angle  
very l e a s t ,  t h e i r  r o l e  must be q u a n t i t a t i v e l y  p a i r s  30°, 40°, 47O, 550 and 65O have e s t ab l i shed  
understood o r  spec t roscopic  s t u d i e s  a t  IUCF can an upper l i m i t  of 0.1 p b / s r 2 ~ e ~  f o r  t he  e x c i t a t i o n  
y i e l d  only q u a l i t a t i v e  information. We be l i eve  of t h e  4.445 MeV 512- s t a t e ;  s e e  Figure l e 2 )  I n  
we have made s i g n i f i c a n t  progress i n  t h e  under- a simple closed-shell  model f o r  12c, t h i s  s t a t e  and 
a companion 712- s t a t e  a t  6.743 MeV cannot be  
formed i n  a s ingle-s tep  proton knock-out. The 
nucleus 12c does not  have s o  simple a ground s t a t e  
SEPARATION ENERGY (MeV) 
wave funct ion ,  but  i t  seems unl ike ly  t h a t  a s ign i -  
f i c a n t  amount of i t  is i n  a form requi red  f o r  
d i r e c t  e x c i t a t i o n  of  these  two s t a t e s .  3, 
The peak a t  about 6.75 MeV i n  Figure 1 has an 
angular  co r r e l a t i on  (see Figure 2) sugges t ive  of an 
L=O knock-out; we conclude t h i s  peak is from 6.793 
MeV 112' s t a t e ,  r a t h e r  than the  6.743 712- s t a t e  a s  
i d e n t i f i e d  i n  an e a r l i e r  100 MeV study.4) 
Figure 1. -4 3- 
It is poss ib l e  t h a t  because of two-step processes 
t he  evidence leading  t o  t h i s  conclusion is i l l u s o r y .  
We s h a l l  examine t h i s  p o s s i b i l i t y  i n  d e t a i l  l a t e r .  
I f  i t  is co r r ec t ,  n e i t h e r  of t h e  two "one-step- 
forbidden" s t a t e s  is exc i t ed  a t  100 MeV i n  a sp -  
metr ic  geometry wi th  approximately equal  energy 
sharing.  It is reasonable t o  conclude t h a t  t h i s  
f a c t  is a consequence of t he  l ack  of appropr ia te  
proton conf igura t ions  i n  t he  12c ground s t a t e  
wave function.  Another p o s s i b i l i t y  is  t h a t  such 
conf igura t ions  do e x i s t ,  bu t  t h a t  t h e i r  e f f e c t s  
a r e  being masked by in t e r f e r ence  caused by two- 
s t e p  processes.  That such e f f e c t s  could p e r s i s t  
over t h e  wide momentum t r a n s f e r  region s tud ied  
seems doubtful .  The ramif ica t ions  of t he  absence 
of d i r e c t  knock-out t o  t he  512- and 112- s t a t e s  
and the  s t r e n g t h  of t h e  112' s t a t e  a r e  being w r i t t e n  
up cu r r en t ly  f o r  publ ica t ion .  
Of t he  16  s h i f t s  awarded t h e  (p,2p) experiment 
f o r  t he  current  period,  about h a l f  have been used 
t o  complete t h e  100 MeV symmetric experiment. 
The remainder, a s  mandated by the  PAC, w i l l  be 
used f o r  a 150 MeV survey and w i l l  be s u f f i c i e n t  
only f o r  a few t a r g e t s .  Prel iminary DWIA cal -  
cu la t ions5)  a r e  being used t o  s e l e c t  appropr ia te  
t a r g e t s  and running condit ions.  
*University of Melbourne, Melbourne, Aus t r a l i a  
1 )  See, f o r  example, Yagi e t  a l . ,  Phys. Rev. 
L e t t e r s  34, 96 (19 75) . 
2) Devins, et  a l . ,  submitted t o  Washington 
meeting, APS, Apr i l  1977. 
3) C.M. McKay and B.M. Spicer ,  Austr. J. Phys. 
28 241 (1975) . 
-9 
4 )  R.K. Bhowmik e t  a l . ,  Phys. Rev. Cx, 2105 
(1976) . 
5) P. Roos, p r i v a t e  communication. 
-44- 


Studies of Knock-Out Reactions

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Studies of Knock-Out Reactions

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