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

Green, M.C.

Hichwa, B.P.

Jacobs, W.W.

Throwe, T.G.

Vigdor, S.E.

Ward, T.E.

English

IUScholarWorks

INVESTIGATIONS OF CONCENTRATED (p,n-) REACTION STRENGTH ON Ca ISOTOPES 
T.G. Throwe, S.E Vigdor, W.W. Jacobs, M.C.  ree en*, and T.E. Ward 
Indiana Univers i ty  Cyclotron F a c i l i t y ,  Bloomington, Indiana 47405 
B.P. Hichwa 
Hope College, Holland, Michigan 49423 
I n  the  continuing inves t iga t ion  l *  * of high-spin 
MSU-83-512 
s t r e t c h e d  o r  near ly-s t re tched 2 p a r t i c l e  (protons) - 1 15 
hole (neutron) s t a t e s  i n  (pyx-) r eac t ions  we have 
completed measurements on 4 8 ~ a ( p , x - ) 4 9 ~ i  a t  Ep = 166 
and 205 MeV and on 4 2 ~ a ( p  , X - ) ~ ~ T ~  a t  Ep = 205 MeV. The 
most recent  data  taken a t  166 MeV, along with  a 
measurement a t  190 MeV taken with the  QQSP spectrometer 
a t  zero degreesS4 have allowed us t o  remove a 
longstanding concern about t h e  energy c a l i b r a t i o n  of 
the  49Ti  spec t ra .  In  both of these  measurements, t he  
ground s t a t e  (p,n') peak was observed with adequate 
s t a t i s t i c s  t o  f i x  the  e x c i t a t i o n  s c a l e ,  allowing us t o  10 
ass ign  energies  of 4.4 + 0.1 MeV and 4.0 + 0.1 MeV t o  
t h e  two s t a t e s  most s t rong ly  exci ted.  Tentat ive  s p i n  
and p a r i t y  assignments of 1912- and 1512- t o  the  4.4 
and 4.0 MeV s t a t e s ,  r e spec t ive ly ,  a r e  supported by a 
number of independent measurements and ca lcu la t ions .  
Recent measurements on ~ ( d  ,a)49 ~i c a r r i e d  out a t  
I U C F ~  have re su l t ed  i n  the  i d e n t i f i c a t i o n  of high-spin I 
s t a t e s  with Jtransfer = 7 a t  e x c i t a t i o n  energies  
cons i s t en t ,  w i th in  e r r o r ,  with the  s t a t e s  seen i n  
5 4 3 2 l . O  5 4 3 2 1 0  
(p ,IT-). 48 ca (a ,  3ny )49 Ti s t u d i e s  have assigned a sp in  Exeltation Energy (MeV) 
and p a r i t y  of 1912- t o  a s t a t e  a t  E, = 4.38 MeV i n  
Figure 1. Comparison between ca lcu la ted  r e l a t i v e  cross  
4 9 ~ i ,  i n  good agreement with our new energy sec t ions  (Ref. 7) and experimental (p ,n') c ross  
s e c t i o n s  f o r  £712- s h e l l  t a r g e t  nuc le i  a t  Ep = 206 MeV 
c a l i b r a t i o n .  I n  add i t ion ,  s h e l l  model ca lcu la t ions  of and @lab = 30'. In the  t h e o r e t i c a l  s p e c t r a ,  t he  
i n d i v i d u a l  s t a t e s  a r e  ind ica ted  by l i n e s  l abe led  by 
B.A. Brown e t  have q u a l i t a t i v e l y  reproduced our L-2Jv, while the  curve rep resen t s  a gauss ian average 
wi th  ~ F W H M  = 0.3 MeV. 
observed spec t ra  (see  Fig. 1) ; s p e c i f i c a l l y  , the  
l o c a t i o n  of the 19/2', 1512' and 1712' s t a t e s  i n  the  another ,  i n  a manner q u a l i t a t i v e l y  cons i s t en t  wi th  
c a l c u l a t i o n  agree ,  wi thin  e r r o r ,  with the  peaks we have expec ta t ions  based on s impl i f i ed  model  calculation^.^ 
i d e n t i f i e d .  Furthermore, the  angular d i s t r i b u t i o n s  The most s t r i k i n g  f e a t u r e  observed i n  the  
measured f o r  the  4.4 and 4.0 MeV t r a n s i t i o n s  a t  Ep = prel iminary ana lys i s  of the  da ta  i s  a remarkable 
166 MeV (see Fig. 2) a r e  very d i f f e r e n t  from one s i m i l a r i t y  i n  the  analyzing. power angular  d i s t r i b u t i o n s  
4 8 ~ a ( a , u - )  4 9 ~ i  Ep = 166 MeV 
- 
$ Ex =4.4 MeV (I9/;) 
8 Ex ~ 4 . 0  MeV (I5/;) 
Figure  2. Cross s e c t i o n  angular  d i s t r i b u t i o n s  f o r  
19/2' (Ex = 4.4 MeV) and 1512- (Ex = 4.0 MeV) s t a t e s  i n  
4 8 ~ a ( p , n - ) 4 9 ~ i  a t  Ep = 166 MeV. 
I of the  s t r e t c h e d  high-spin s t a t e s  of t he  two t a r g e t s  I (Fig. 3). This f e a t u r e  is  even more s t r i k i n g  when one 
compares these  angular  d i s t r i b u t i o n s  with those of 
s t r e t c h e d  s t a t e s  populated i n  180(p,x-)19~e8 and 
8 8 ~ r ( p , n - ) 8 9 ~ r . 9  I n  a l l  fou r  cases  one sees  the  same 
I s t r u c t u r e  i n  the  angular  d i s t r i b u t i o n  -- A, i s  negat ive  I forward of 60°, with a r ap id  r i s e  t o  p o s i t i v e  values  a t  I back angles.  These s i m i l a r i t i e s  over a wide range of 
t a r g e t  mass and f i n a l  s t a t e  sp in ,  when con t ra s t ed  with 
I t he  d i s s i m i l a r i t y ,  i n  each case ,  of t he  d i s t r i b u t i o n s  I f o r  t he  h ighest  and next-highest sp in  s t a t e s ,  suggests  
t h a t  t he  observed analyzing power d i s t r i b u t i o n s  may 
I c o n s t i t u t e  an experimental  s igna tu re  f o r  t he  popula t ion I of s t r e t c h e d  s t a t e s  i n  the  (p,n-) r eac t ion .  As of y e t ,  
however, we cannot simply exp la in  the  observed 
analyzing power sys temat ics .  
$ * ' ~ r  Ex = 4.3 MeV ('y) 
$ 4 9 ~ i  EX ~ 4 . 4  MeV (IT) 
4 4 3 ~ i  EX ~ 3 . 1  MeV (I%) 
$ I 9 ~ e  Ex ~ 4 . 6  MeV ( 'y) 
1.0 
Figure  3. Analyzing power angular  d i s t r i b u t i o n s  f o r  t he  
2p-lh s t r e t c h e d  s t a t e  conf igu ra t ions  exc i t ed  i n  the  
(pyx-) r e a c t i o n  on t a r g e t  nuc le i  8 8 ~ r  (Ref. 9, Ep = 175 
MeV), 4 8 ~ a  (Ep = 166 MeV), 4 2 ~ a  (Ep = 205 MeV), and 180 
(Ref. 8, E = 201 MeV). (She l l  model c a l c u l a t i o n s  
i n d i c a t e  t p a t  t he  4 3 ~ i  s t a t e  may be a double t  with 
s p i n s  1912- and 15/2-. ) 
.8 
A p e r s i s t e n t  f e a t u r e  of t he  continuum reg ion  of 
(&T-) Stretched State Analyzing Powers 
- 
a l l  (pyx-) s p e c t r a  from t a r g e t s  with A 2 30 is  a nea r ly  
l i n e a r  r i s e  i n  the  x- y i e l d  beginning a t  o r  near  the  
l o c a t i o n  (or  suspected l o c a t i o n )  of t he  s t r e t c h e d  
s t a t e s .  This l i n e a r  r i s e  l ed  us t o  specu la t e  t h a t  t he  
low-lying 2p-lh high-spin s t a t e s  were a c t i n g  a s  
"doorways" i n t o  more complicated s t a t e s  i n  the  
continuum region reached v i a  r e s c a t t e r i n g  of the  n'. 
This specu la t ion  was r e in fo rced  by the  observed 
s i m i l a r i t y  i n  c ross  s e c t i o n  angular  d i s t r i b u t i o n  shapes 
f o r  Ep = 205 MeV between two e x c i t a t i o n  energy regions  
i n  the  continuum of 4 9 ~ i  (<Ex> = 10.0 MeV and ax> = 
5.5 MeV) and the  concentra ted  high-spin s t r e n g t h  region 
near  Ex = 4 MeV ( see  upper r i g h t  frame of Fig. 4). 
48 48 Ca (KT-), ED= 166 MeV Ca (KT-), ED= 205 MeV 
Figure 4. Cross sec t ion  and analyzing power 
comparisons of two regions  of the  continuum 
(<Ex> = 10.0 MeV and <Ex> = 5.5 MeV) with  t h a t  of the  
concentra ted d i s c r e t e  s t r e n g t h  i n  the  4 8 ~ a ( p  , X - ) ~ ~ T ~  
spectrum a t  Ep = 166 and 205 MeV. 
When one looks a t  the  166 MeV da ta  one again  sees  the  
two e x c i t a t i o n  energy regions  t r ack  each o t h e r ,  but the  
comparison with the  s t r e n g t h  concentra t ion i s  l e s s  
convincing. S imi la r ly ,  the  analyzing powers p l o t t e d  i n  
t h e  lower half  of Fig. 4 show a f a i r  amount of 
consis tency between d i f f e r e n t  regions  i n  the  continuum, 
but the  analyzing powers of the continuum do not slmply 
t r a c k  t h a t  of the  s t r e n g t h  concentra t ion.  Hence i n  
l i g h t  of the  166 MeV da ta ,  t he  idea  t h a t  the  s t rong  
d i s c r e t e  s t a t e s  a c t  a s  doorway s t a t e s  f o r  the  continuum 
region appears l e s s  ce r t a in .  A f u l l e r  understanding of 
t h e  energy dependence of do/dQ and Ay f o r  both the  
d i s c r e t e  and continuous p a r t s  of the  s p e c t r a  over a 
broader energy range (up t o  the  A resonance regime f o r  
t h e  outgoing pions) f o r  4 8 ~ a  (as  we l l  a s  o ther  t a r g e t  
n u c l e i )  may help shed l i g h t  on t h i s  quest ion.  
"present address:  Physics Divis ion,  Argonne National 
Lab, 9700 S. Cass Avenue, Argonne, IL 60439 
1)  S.E. Vigdor e t  a l . ,  Phys. Rev. Let t .  2, 1314 
( 1982). 
2) S.E. Vigdor e t  a l . ,  IUCF S c i e n t i f i c  and Technical 
Report 1982, p. 75. 
3) T.G. .Throwe e t  a l . ,  ib id . ,  p. 93. 
4 )  T.E. Ward e t  a l . ,  t h i s  Report, p. 82. 
5) H. Nann e t  a l . ,  i b id . ,  p. 115. 
6) M. Behar e t  a l . ,  Nucl. Phys. A=, 61 (1981). 
7) A. Brown e t  a l . ,  Phys. Rev. Let t . ,  51, 1952 (1983). 
8)  J.J. Kehayias e t  a l . ,  Bull. Am. P ~ Y s -  Sot. 28, 705 
(1983). 
9) M.C. Green e t  dl., t h i s  Report, p. 76. 


Investigations of Concentrated (p, pi ̄ ) Reaction Strength on Ca Isotopes

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Investigations of Concentrated (p, pi ̄ ) Reaction Strength on Ca Isotopes

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