Supported by the National Science Foundation and Indiana Universit

Friesel, D.L.

Kailas, S.

Pickar, M.

Pile, P.H.

Pollock, R.E.

English

IUScholarWorks

TIPI-2 rms 
FILE . 3. 
CHANNEL NUUBER 
Fi-qure 2. ~e Zayed proton spectrwn observed fo ZZowing 
f 75 MsV proton bombardnent of  2 4 ~ g .  The energies 
Zisted are the Zaboratory proton energies associated 
with the various peaks. The 5.40 MeV peak appears t o  
decay a t  a ra te  consistent with tha t  of 2 5 ~ i .  
dominant 2 5 ~ i  peak a t  4.089 MeV should be seen.  I n  
t h e  next run,  use of a  1000 um t h i ck  de t ec to r  and 
modificat ion of t he  t a r g e t  assembly geometry t o  take 
advantage of t h e  unique kinematics of t h e  (p,n-xn) 
r eac t ions  near threshold  a r e  expected t o  improve the  
signal- to-noise r a t i o .  Rela t ive ly  c lean  2 5 ~ i  peaks 
have been observed with lower background by using 
longer delays p r i o r  t o  t he  i n i t i a t i o n  of counting. 
This al lows t h e  s h o r t e r  l i ved  2 1 ~ g ,  17Ne, and 9~ 
a c t i v i t i e s  (Q 110-130 ms) t o  decay t o  a g rea t e r  
ex t en t  than the  2 5 ~ i  a c t i v i t y  (220 m s )  . This,  how- 
ever ,  reduces t h e  o v e r a l l  counting e f f i c i e n c y  con- 
s ide rab ly .  We bel ieve  t h a t  t he  planned s t e p s  w i l l  
make a s i g n i f i c a n t  improvement of t he  da t a  q u a l i t y  i n  
our next  run. I n  add i t i on ,  we p lan  t o  i n s t a l l  160 
t a r g e t s ,  i n  which case t he  only background protons 
w i l l  a r i s e  from 9~ and the  17Ne a c t i v i t y  and should 
be correspondingly e a s i e r  t o  de t ec t .  I n  t h i s  case,  
only two s t a t e s  of 7 ~ e  a r e  p a r t i c l e  s t a b l e .  
RECOIL DETECTION OF THRESHOLD PION REACTIONS 
R.E. Pollock, M. P ickar ,  P.H. P i l e ,  S. Kai las ,  and D.L. F r i e s e l  
Indiana University Cyclotron Faci l i ty ,  BZoomington, Indiana 47405 
The technique of observing the  (p ,nO)  r eac t ion  the  r e c o i l  experiment can provide information on t h e  
threshold by de t ec t ion  of t he  product nucleus 0' r e c o i l  exc i ted  s t a t e  c r o s s  s ec t ion  independent of absolu te  
was described i n  t he  I U C F  1978 r epo r t .  During 1979 normalizat ion of t he  r e c o i l  de t ec t ion  e f f i c i ency .  
t h i s  technique was appl ied  t o  t he  r eac t ions  The e x c i t a t i o n  funct ion  f o r  t he  r e c o i l  y i e l d  is 
g ~ e ( p , n O ) l  O B ( ~ .  s . )  and 9 ~ e ( p , n 0 )  OB*(E~ =1.74 MeV). The shown i n  Fig. 1. The method used t o  change cyclo t ron  
exci ted  s t a t e  is of p a r t i c u l a r  i n t e r e s t  a s  t he  t h i r d  energies  by a f r a c t i o n  of an MeV requ i r e s  only a few 
+ 
member of an i sosp in  t r i p l e t  f o r  which t h e  ' ~ e ( ~ , n  ) l O ~ e  minutes so t h a t  many da t a  po in t s  could be taken i n  a run 
cross  s ec t ion  has been r ecen t ly  determined wi th in  2 MeV of 2 o r  3 s h i f t s .  The r i g h t  s i d e  of t he  f i g u r e  shows 
1 
of threshold  , and f o r  which t h e  9 ~ e ( p , ~ ' )  ~ O C ( ~ .  s  ,) c r o s s  a search f o r  t h e  threshold  ' B ~ ( ~ , I T - )  O C ( ~ . S )  r e a c t i o n  
sec t ion  is known a t  higher energy. The by the  same apparatus.  The de t ec to r  i n  t h i s  run was 
9 ~ e ( p , n 0 ) 1 0 ~ e ( g . s . )  c r o s s  s ec t ion  has  r e c e n t l y  been in-  s e t  f i r s t  f o r  mass-10, charge s t a t e  5+, f o r  which i t  was 
dependently determined by a d i f f e r e n t  technique2 so t h a t  s e n s i t i v e  t o  a l a r g e  background from the  t o t a l  (p,nof 
PREDICTED 
..jWT= 4nb.l 
10 
Figure I .  ( l e f t )  Excitation 
y i e l d  f o r  t he  s eve ra l ,  pa r t i c l e - s t ab l e  s t a t e s  of l ag ,  This apparatus has  been dismantled t o  make room f o r  
a s  well  a s  t h e  (p,a-)  process of i n t e r e s t ,  and a l t e r n a -  t he  QQSP spectrograph.  The f i n a l  r e s u l t s  of t h e  measure- 
t i v e l y  set f o r  6' r e c o i l s  t o  r e j e c t  t h e  ' O B  background. ment and a f u l l  de sc r ip t ion  of t h e  technique w i l l  be 
1 1  1 I 1 1  
t 
- YIELD - 
(EVENTS/p COUL) S~e(p,rrO)  'OB [xT= 1.8 mg/cm2] - 
Preliminary a n a l y s i s  of t h i s  da t a  gives an upper bound prepared f o r  publ ica t ion .  
' 8 ~ 1 I t I I I 1  
6-  Q-5 
t o  t h e  (p  ,IT-) y i e l d  which is somewhat smal ler  than ex- 
1 )  R.E. Marrs, R.E. Pollock,  and W.W. Jacobs,  Phys. Rev. 
pected by ex t r apo la t ion  downward i n  energy,from t h e  s i n g l e  C 20, 2308 (1979). 
ftatction f o r  the recoi l  yield 8 - for the Be (p, T O )  l OBe reaction. P Arrows show the threshold or - 
vaarious excited s ta tes  o f  {'Be. . 6 1 - 
( r igh t )  Ex& ta t ion  function 
search for the threshold for 
the Be I ~ ,  n-) OC m a c t i a .  The 4 
known cross  s ec t ion  va lue  from Uppsala, us.ing t h e  pen- 2) M. P ickar ,  IUCF Experiment 18, repor ted  elsewhere i n  
t h i s  volume. See a l s o  M. P ickar ,  e t  a l . ,  Bull .  Am. 
e t r a b i l i t y  and phase space funct ions  which desc r ibe  Phys. SOC. 24, 819 (1979) 
144.0 145.0 146.0 
Tp (MeV)-, 
4  YIELD - 
2-  
i n s e t  figure shows the predicted 
energy dependence o f  the cross 
section a t  threshold. 2-  
+ 
t he  O B  (p  ,a ) 'B (g. s . ) energy dependence. 3) P.H. P i l e  e t  a l . ,  Phys. Rev. Le t t .  42, 1461 (1979). 
0 
- 
- 
T= l - 
t 
6 t 
0.72 
t 
1.74 1 g.s 
O a " ~ L 1 l l ~ " ' l " '  
ACTIVATION MEASUREMENTS OF THE 8 ~ b  ( 3 ~ e ,  a'xn) l - X n ~ t  REACTION 
- 
Q = 6  ,a ----- LQ-g--P-- 
, , , , ,  
1 g.s.(7r-1 
1 
T.E. Ward, W.W. Jacobs, D.  F r i e s e l ,  R.D.  Bent, and P.P. Singh 
Indiana University CycZotron Faci Zity,  BZoomingtun, ~nd iana  4 7405 
152.0 153.0 
Tp (MeV) - 
P. P i l e  
Carnegie Me ZZon University, Pittsburgh, Pennsy Zvania 1521 3 
The 8 ~ b  ( 3 ~ e ,  a'xn) -XnAt r eac t ion  is being i n t e r n a l  momentum of t h e  nucleons i n  3 ~ e ,  i t  y i e l d s  % 
s tud ied  radiochemically by measuring the  r e s i d u a l  a- 1 nb. Wall e t  a1.' repor ted  a 1 2 ~ ( 3 ~ e , n 0 )  c r o s s  s e c t i o n  
a c t i v i t y  of  t h e  a s t a t i n e  i so topes .  A measurement of of 5 0.007 n b / s r - M ~ V  a t  200 MeV bombarding energy, 
t he  ( 3 ~ e , a - )  y i e l d  a t  energies  wel l  below t h e  f r e e  y i e ld ing  a t o t a l  c ros s  s e c t i o n  of t he  order  of 2 1 nb. 
+ - 
nucleon-nucleon pion threshold  can be used t o  t e s t  f o r  More r ecen t ly  Benenson e t  a1. have measured t h e  a /r 
c o l l e c t i v e  e f f e c t s  i n  pion production using complex y i e l d s  produced by 2 0 ~ e  heavy ions  from 85-400 MeV/ 
1 p r o j e c t i l e s .  Bertsch has  ca l cu l a t ed  pion-production nucleon on a number of t a r g e t s .  Those r e s u l t s  compare 
i n  heavy ion  c o l l i s i o n s  and has  shown t h a t  neglec t ing  favorably with t he  Bertsch type ca l cu l a t i on  and i n d i c a t e  
c o l l e c t i v e  e f f e c t s ,  t he  ( 3 ~ e ,  IT) r eac t ion  c ros s  s ec t ion  t h a t  t he  production of pions with complex p r o j e c t i l e s  
a t  70 MeV/nucleon g ives  zero  and by inc luding  t h e  i s  cons i s t en t  with h i s  s imple model. 


Recoil Detection of Threshold Pion Reactions

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Recoil Detection of Threshold Pion Reactions

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