Supported by the National Science Foundation and Indiana Universit

Ahmad, M.

Anderson, B.D.

Baldwin, A.R.

Fazely, A.

Foster, C.C.

Knudson, J.

Madey, R.

Tandy, P.C.

Walker, G.

Watson, J.W.

English

IUScholarWorks

3~ (p, n) 3~ AT INTERMEDIATE ENERGY 
C.A. Goulding and M.B. Greenfield 
FZorida AM University, TaZZahassee, PZorida 32303 
C.C. Fos ter  and C.D. Goodman 
Indiana University CycZotron Facility,  BZoomington, Ind{ana 47405 
T. Masterson and E. Sugarbaker 
University of Co Zorado, Boulder, CoZorado 80309 
9. Horen 
Oak R.idge NationaZ Laboratory, Oak Ridge, Tennessee 37830 
J. Rapaport 
Ohio University, Athens, Ohio 43701 
D. E. Bainum 
Emporia State University, Ernporia, Kansas 66801 
Neutron energy s p e c t r a  from 3 ~ ( p , n )  3~ were t i o n s  with an  i n t e r a c t i o n  taken from t h e  work of W.G. 
measured a t  E =80, 120, and 160 MeV a t  s c a t t e r i n g  angles Love and derived from the  f r e e  N-N force .  P 
from 0' t o  26O. From these  spec t r a  d i f f e r e n t i a l  c ros s  Within t h e  context  of t h i s  ana lys i s  t h e  sharp  
sec t ions  have been obtained f o r  1 3 ~ ( p , n ) 1 3 ~ ( g . s . )  and minimum r e s u l t s  from in t e r f e r ence  between J=1 c e n t r a l  
3 ~ ( p , n )  3 ~ ( 3 . 5  MeV) f o r  E -120 and 160 MeV. The t r a n s i -  and tensor  components of t he  force .  This i n t e r f e r e n c e  P 
t i o n  t o  t he  3.5 MeV exci ted  s t a t e  is 1 / 2 5  312- and has is not  observed i n  t h e  t r a n s i t i o n  t o  t he  3.5 MeV s t a t e  
an  angular  d i s t r i b u t i o n  charac ter ized  by a rapid  mono- because the  c e n t r a l  component dominates. I n  t h e  ground 
ton ic  f a l l - o f f  with increas ing  angle,  s i m i l a r  t o  o the r  s t a t e  t r a n s i t i o n ,  which is p1,2+p1,2, t h e  c e n t r a l  compo- 
cases of sp in - f l i p ,  i so sp in - f l i p  t r a n s i t i o n s .  The l a r g e  nent is weaker. The J = O ,  sp in  independent i so sp in  term 
0' cross  s e c t i o n  a l s o  i nd i ca t e s  t h a t  t h i s  s t a t e  conta ins  i n  t h e  i n t e r ac t ion ,  which a l s o  con t r ibu t e s  incoherent ly  
most of t h e  GT s t r eng th  f o r  3 ~ + 1  3 ~ .  The ground s t a t e  t o  t he  ground s t a t e  t r a n s i t i o n ,  exh ib i t s  a  monotonic 
t r a n s i t i o n ,  which is 112-+1/2-, shows a s t ruc tu red  an- f a l l - o f f  wi th  angle  i n  t he  ca l cu l a t i ons .  
gular  d i s t r i b u t i o n  with a sharp  minimum a t  about 20'. 1 )  W. G. Love i n  "The (p,n) Reaction and t h e  Nucleon- 
Nucleon Force", ed i t ed  by C.D. Goodman, S.M. Austin, 
These r e s u l t s  have been analyzed using DWIA ca lcula-  S.D. Bloom, J. Rapaport and G.R. Sa t ch l e r ,  Plenum, 
New York,1980, p. 23. 
HIGH-SPIN STATES I N  NUCLEI EXCITED V I A  THE (p,n) REACTIONS 
B.D. Anderson, M. Ahmad, A.R. Baldwin, A. Fazely, J. Knudson, R. Madey, P.C. Tandy, and J . W .  Watson 
Kent State University, Kent, Ohio 44242 
C.C. Fos ter  and G.  Walker 
Indiana University Cyclotron Facility,  Bloonrington, Indiana 47405 
In  our October 1979 run,  we s tudied  the  e x c i t a t i o n  r a to ry  angles from 24' t o  48.5'. We used a 0.52 m2 x 
of high-spin s t a t e s  i n  t he  1 2 ~ ( p , n ) 1 2 ~  and 1 6 0 ( * , n ) 1 6 ~  10 cm th i ck  de t ec to r  a r r ay  a t  68.0 m i n  t he  f i r s t  
r eac t ions  a t  99 MeV bombarding energy. This was t he  de t ec to r  s t a t i o n  (0' t o  24.5') and a 0.77 m2 x 10 cm 
f i r s t  run t o  use a second de t ec to r  s t a t i o n  wi th  t he  t h i ck  de t ec to r  a r r ay  a t  76.3 m i n  the  second de t ec to r  
beam swinger f a c i l i t y  which permitted access t o  labo- s t a t i o n  (24' t o  48.5'). Overal l  energy r e so lu t ions  
of 260 keV and 230 keV were achieved a t  t he  f i r s t  and 
second de t ec to r  s t a t i o n s ,  r e spec t ive ly ,  f o r  neutrons 
of about 80 MeV from the  1 2 ~ ( p , n )  1 2 ~  r eac t ion .  The 
23 mg/cm2 C t a r g e t  cont r ibuted  % 150 keV t o  these  
observed resolu t ions .  
Figure 1 shows the  48.5' spectrum of neutrons 
from the  160(p,n) l E F  r eac t ion .  A t  t h i s  angle a s i n g l e  
peak a t  6.4 MeV e x c i t a t i o n  dominates t he  1 6 ~  spectrum. 
We i n t e r p r e t  t h i s  peak t o  be t h e  4' s t a t e  with a 
-1 
(d5/29p3/2 ) proton-par t ic le  neutron-hole "stretched" 
con£ igu ra t ion  predic ted  by Mof f a  and walker. ' A s  
seen i n  Fig. 2, t he  angular  d i s t r i b u t i o n  f o r  t h i s  
s t a t e  has a c h a r a c t e r i s t i c  L=3 shape cons i s t en t  with 
t he  5'=4- i n t e r p r e t a t i o n ;  i. e .  , t h e  angular  d i s  tri- 
but ion  peaks near  t he  momentum t r a n s f e r  q = L/R = 
3/(1.15 fm) = 1.035 fm-1(8CM%350). The e r r o r  
F i g m e  2. The angular  d i s -  
t r i b u t i o n  of t h e  high-spin 
s t a t e  i n  1 6 ~  from the  
160(p,n) 1 6 ~  (6.2 MeV) reac- 
t i o n  a t  99.1 MeV. The 
c i r c l e s  r ep re sen t  c r o s s  
s ec t ions  t h a t  were e x t r a c t e d  
from the  first d e t e c t o r  sta- 
t ion;  t he  t r i ang le s ,  from 
the  second. 
w n  
.> t 9 9 . 1  Ye" 
10 s 0 
LXCITATION LNLRCY, L ( M e V )  
X 
Figure 1. The neutron energy spectrum a t  a Zaboratory 
angle  of 48.5' from the  160(p ,n )16~  r e a c t i o n  a t  99.1 
MeV. 
ba r s  shown i n  Fig. 2 r e f l e c t  s t a t i s t i c a l  e r r o r s  only.  
Systematic e r r o r s  of about 20 percent  i n  t h i s  experi-  
ment a r e  dominated by an uncer ta in ty  i n  t he  neutron 
L - 
99.1 MeV 
- - 
- 160(p,a)16~ (6.4 MeV, 4') - 
- - 
- i A - 
m I - 
- - 
- - 
N E U T R 0 N A N G L E , Om (DEGREES) 
+A' 
10 3 0 
CXCXTATXON CNCREY, f X C Y o V )  
Figwe 3. The neutron energy spectrum a t  a Zaborator2 
angle of  48.5' from the 12~(p,n)12~ reaction a t  99.1 
MeV. 
detection efficiency because the detected neutron 
energies are too close to the detection threshold. 
Figure 3 shows the 48.50 spectrum of neutrons 
from the 12~(~,n):2~ reaction at 99 MeV. The prominent 
peak at about 4.2 MeV excitation is believed to be the 
4- "stretched" state predicted by Moffa and Walker for 
1 2 ~ .  Recently, Morris et a1.2 suggested that the ana- 
log of this state at 19.65 MeV excitation in 12c is 
one member of a highly isospin-mixed doublet of 4' 
states, with the other member at 19.25 MeV. This sug- 
testion is based on differences in the yields for IT' 
and IT' inelastic scattering from 12c near the (3,3) 
resonance energy. The observed width of the peak at 
4.2 MeV excitation in Fig. 3 is substantially larger 
than our 230 keV resolution. Until we complete the 
analysis of our data at each of the measured angles 
from 0' to 48.5' in steps of about 6', we are unable 
to comment on whether the observed peak is likely to 
be a single state with an intrinsic width of a few 
hundred keV or whether it could be two unresolved 
states. Since the 12c (p ,n) 12N reaction must populate 
states with T a ,  we should observe an analog of only 
one of the states proposed by Morris et al. It may 
be necessary to study this reaction again at longer 
flight paths and larger momentum transfers to clarify 
this point. 
The study of these high-spin states complements 
studies of analog states and Gamow-Teller states by 
focusing on tensor terms in the nucleon-nucleon effec- 
tive interaction with specific values of orbital- 
angular-momentum trans£ er . Lindgren et a1. showed 
from a systematic comparison of (e,el) and (p,pl) 
transition strengths to unnatural parity states of 
"stretched" (j = maximum) configurations that the 
available data emphasize the isovector part of the 
tensor force. Since the one-particle radial form 
factors can be determined from inelastic electron 
scattering where the projectile-target interaction is 
known, the excitation of such "stretched" high-spin 
states in (p,n) and (p,pl) reactions provides a mod- 
erately well-understood framework in which to study 
the tensor terms in various models of the effective 
nucleon-nucleon interaction. 
In addition to studying the 4' high-spin states 
in 12N and 1 6 ~ ,  we extracted differential cross sec- 
+ tions for the 1 2 ~  ground state (~"=l ) from the 
12~(p,n) data. These cross sections are presented 
in Figs. 4 and 5 along with DWIA calculations from 
Love which use an effective nucleon-nucleon inter- 
ac tion4 derived from the free nucleon-nucleon force. 
For the ground state, the calculation agrees with 
the data out to about 30' and falls significantly 
below at wider angles; for the 0.96 MeV state, the 
calculation must be reduced by 35% to obtain agree- 
ment with the data at forward angles. A similar 
comparison4 of DWIA calculations with the 12~(p,p')12~* 
data of comfort5 at 122 MeV appeared on page 93 of 
the IUCF Technical and Scientific Report of last year. 
An abstract on the 99 MeV 12c data was submitted to 
the American Physical Society for presentation at 
F<we 4. The angular distribution of the I+ ground 
state  i n  12N from the 12c(p,n)12N reaction a t  99.1 
MeV. The smooth curve i s  a DWIA f i t  with a combina- 
t ion of central, tensor and spin-orbit interactions 
including exchange terms. 
the April 1980 meeting in Washington, D.C. A paper 6 
comparing earlier data from the 12c(p,n)12~ reaction 
at 62 and 120 MeV with 12c(p,p') data was accepted 
for publication. 
1) P.J. Moffa and G.E. Walker, Nucl. Phys. A22, 140 
(1974) . 
2) C.L. Morris et al., Phys. Lett. 9, 38 (1978). 
8 (DEGREES) cm 
Figure 5. The angular distribution o the 2+ state  f a t  0.96 MeV i n  12N from the 12c(p,n) l N reaction a t  
99.1 MeV. The smooth curve i s  a DWIA f i t  with a 
combination of central, tensor and spin-orbit inter-  
actions including exchange terms. 
3) R.A. Lindgren et al., Phys. Rev. Lett. 42, 1524 
(1979). 
4) W.G. Love, Conference on the (p,n) Reaction and 
Nucleon-Nucleon Forces (Telluride, 1979); and 
private communication. 
5) J. Comfort et al., Bull. Am. Phys. Soc. 24, 829 
(1979). 
6) B.D. Anderson et al., Nucl. Instrum. Methods (in 
press). 


High-Spin States in Nuclei Excited Via the (p,n) Reactions

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High-Spin States in Nuclei Excited Via the (p,n) Reactions

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