This work was supported by the National Science Foundation Grant NSF PHY 81-14339 and by Indiana Universit

Bent, R.D.

Green, M.C.

Huber, M.G.

Hugi, M.

Kehayias, J.J.

Kienle, P.

Pollock, R.E.

Rehm, K.E.

Scheerer, H.J.

Schott, W.

English

IUScholarWorks

PION PRODUCTION 
MEASUREMENT NEAR THRESHOLD OF gBe(3~e  ,n)  TO THE A = 12 ISOBARIC TRIPLET BY RECOIL DETECTION 
R.D. Bent, M.C. Green, M. Hugi, J.J. Kehayias, and R.E. Pollock 
Indiana University Cyclotron F a c i l i t y ,  Bloomington, I N  47405 
K. E . Rehm 
Argonne National Laboratory, Argonne, I l l i n o i s  60439 
P. Kienle, H. J. Scheerer, and W. Schott 
Physik-Department, Technische Universi ta t  Munchen, Munich, W. Germany 
M.G. Huber 
Universi ta t  Erlangen-Nurnberg , Erlangen, W. Germany 
The study of near-threshold, pion production monitored by insu la ted  i ron  blocks. A 2.1 m long 
react ions t o  d i s c r e t e  s t a t e s  by measuring the reco i l s  horizontally-widened vacuum box with the Faraday cup a t  
with the l a rge  s o l i d  angle IUCF QQSP spectrometer and a i t s  end has been connected t o  the port and shielded by 
heavy ion foca l  plane detector1 i s  a favorable a 1 m l ayer  of i ron  and concrete. 
method, because angular d i s t r i b u t i o n s  over a wide or  For c a l i b r a t i n g  the detector  the r e c o i l s  from the 
complete range can be obtained f o r  several  react ion react ions 6 ~ i  (p, n0)7Be and 7 ~ i  (p, n-) 8~ were measured. 
channels simultaneously with a s ing le  angle and This was done with a 171.15 MeV p-beam and a 0.3 mg/cm2 
magnetic f i e l d  se t t ing .  na tu ra l  C-target. Detection of the high f l u x  of 
The maximum s c a t t e r i n g  angle elmax of the reco i l s  a - p a r t i c l e s  (3  kHz a t  15 nA beam cur ren t )  was 
i n  the pion production react ions considered is about 6" suppressed by ra i s ing  the discr iminator  l e v e l  of the 
o r  half of the QQSP horizontal  angle acceptance of E-and AE-signals . 
11.5'. Therefore, the incident  beam must leave the A l l  "pionic fusion" measurements were made using a 
spectrograph through the "0"" port.  The beam is 
bent s l i g h t l y  i n  t ravers ing the f i e l d  of the f i r s t  
dipole  of the s p l i t  pole and i n  t rave l ing  about 28 cm 
i n  the reduced f i e l d  region between the poles. The 
beam def lec t ion  l i m i t s  the f i e l d  l eve l  which can be 
applied without losing too much beam a t  the e x i t  port. 
The maximum r i g i d i t y  of the r e c o i l  p a r t i c l e s ,  which 
can be analyzed a t  the foca l  plane within the given 
range of momenta (p/po = 0.83 .. . 1.35, where po means 
the  momentum with nominal radius  po = 0.36 m) is, thus, 
a l s o  determined. For the r e c o i l s  considered, maximum 
transmission through the port has been achieved by 
s e t t i n g  the spectrograph t o  8 -5.7'. Thus p a r t i c l e s  
with 81 = 0' and elmax appear a t  the low end and i n  the 
middle of the acceptance range respectively. The par t  
of the beam current  h i t t i n g  the end of the port was 
7 3 
198.5 MeV 3 ~ e  beam. The react ions leading t o  12B, 
12c, 1 2 ~  r e c o i l s  (corresponding t o  n+, T O ,  n', 
respect ively) ,  were invest igated with severa l  types of 
Be t a r g e t s ,  including two thicknesses of s e l f -  
supporting t a rge t s ,  and others  with 0.5 mg/cm2 Au 
backing. Furthermore, some beam time was spent with 
such other  t a r g e t s  as  llB, 12c, Li20 and melamine2 t o  
study the f e a s i b i l i t y  of detect ion of s t i l l  heavier 
recoi ls .  
Since the September data-taking run we have 
analyzed only the longest run with the 0.5 mg/cm2 
- 
Be target .  For Z i d e n t i f i c a t i o n  JE*AE a Z 4; was 
calculated from the E and a signals .  Both s igna l s  
were corrected f o r  the angle of incidence of the 
p a r t i c l e s ,  measured r e l a t i v e  t o  the normal t o  the foca l  
l ine .  The angular range is 29' t o  63". The angle is 
determined by measuring the p a r t i c l e  posi t ion x l  i n  the 
foca l  plane and x2 a t  a locat ion 4.4 cm behind it. 
The posi t ion and angle information was ca l ib ra ted  
p r io r  t o  the run by means of one of the two l i n e s  of a 
ThC a source which was put a t  the t a rge t  position. 
Gains and o f f s e t s  of x l  and x2 were obtained by 
measuring the event posi t ions with d i f f e r e n t  f i e l d s  and 
using the cor re la t ion  between p/po and ac tua l  foca l  
plane posi t ion which is known from beam o p t i c a l  
calculat ions.  
A one-dimensional window on Z=5 and 6 was s e t  i n  
the spectrum, which was accumulated using only 
angles i n  the above mentioned range. A two-dimensional 
window on mass 12 was s e t  i n  the E(xl)-histogram, which 
was sor ted with angle and Z conditions. In  Fig. 1 
i s  shown the resu l t ing  angle versus XI-histogram, which 
was obtained with Z, mass, and angle conditions. The 
curve a and the half e l l i p s e s  b and c correspond t o  
kinematic ca lcu la t ions  using the angle and 
X I  parameters which were obtained from the measurement 
with the a source. There would appear t o  be events i n  92 
excess of background on the locus a )  corresponding t o  
the 9 ~ e ( 3 ~ e , n + ) 1 2 ~  bound s ta tes .  The 12c-events 76 
4-l 
disappear, as  they should, when the Z-window is s e t  on E 
2 
L 
215. Some of the 216, A=l2 events may come from the - 
e, 
"pionic fusion" react ion because they appear t o  follow 
E 60 
b i 
the  curves b and c ,  espec ia l ly  a t  small p/po. The o 
s p a l l a t i o n  background from beam-induced breakup of 4+ 
heavy impuri t ies  i n  the t a rge t  gives events d i s t r ibu ted  
spectrometer entrance. The preliminary da/dQ-values a re  
0.7, 0.6 and 0.4 nb/sr.  d a / d ~  f o r  the n+, 12B5+ 
- react ion could be s l i g h t l y  too high due t o  events from 
the no,  12c5+-and no, (15.11 MeV) - react ions 
which l i e  c lose t o  curve a. The integrated charge f o r  
t h i s  spectrum was 1.4 m Coul. The e f f i c iency  of the 
pos i t ion  wires was measured t o  be 59 percent and dead 
time losses  were calculated t o  be 50 percent. There is 
a h in t  of s t r u c t u r e  i n  Figure 1 corresponding t o  another 
half e l l i p s e  with a center  a t  p/po=l.28 a t t r i b u t e d  t o  
llB r e c o i l s  which appear i n  the spectrum because of 
imperfect mass separation. Such l l B  r e c o i l s  could 
r e s u l t  from the 9 ~ e ( 3 ~ e , n x + )  l l B  react ion,  where the 
neutron, which is evaporated during or  a f t e r  the 
emission, c a r r i e s  l i t t l e  momentum. Resonant exc i ta t ions  
of 1 1 ~  with neutrons around 1 MeV a r e  known. 
over the plane and s e t s  a lower l i m i t  t o  the observable 44 60 76 
cross  sec t ion  by t h i s  method. For a rough analysis  the channel number 
curve a was subdivided i n t o  three equal angle par t s  
corresponding t o  center  of mass s c a t t e r i n g  and s o l i d  Figure 1. Sca t te r ing  angle versus pos i t ion  histogram. 
e l0  means the angle i n  the l a b  system measured from the 
angles of 8 = 7.5', 23.2', 41.8' and dP = 0.11 s r ,  spectrometer symmetry a x i s  ( sca t t e r ing  angle 
01 = 5. 7°-810). The var iab le  p/po i s  the path radius  
0.38 sr, 0.59 sr. The s o l i d  angle a t  41.8' is s l i g h t l y  r e l a t i v e  t o  the nominal value 0.36 m. The curves a r e  
kinematics ca lcu la t ion  r e s u l t s  f o r  the react ions:  
reduced by the f 50 m r  a x i a l  angle aper ture  a t  the a. 9~e(3~e,x+)11~5+g.s .  ; b. 9~e(3JJe,z0)12~6+Cr.s. 
c. 9~e(3He,x0)12~6+(15.11 MeV). 
The Munich group would l i k e  t o  thank W. Benenson, who 2) The s e l f  suppor t ing Be t a r g e t s  were manufactured by 
suggested measuring heavy ion  pion production us ing the  H. Adair,  ORNL, Be on Au was made by H. Maier, 
r e c o i l  method. Sekt ion Physik de r  LMU, Munich, Li20 and Melamine 
by P. Maier - Komor, Physik - Department der  TUM. 
1 )  J.R. Erskine e t  a l . ,  Nucl. I n s t r .  and Methods 135, 
57 (1976). 3) F. Ajzenberg-Selove, Nucl. Phys. A248, 1 (1975). 
THE DOMINANCE OF HIGH-SPIN TWO-PARTICLE ONE-HOLE TRANSITIONS I N  (p,x-) REACTIONS 
S.E. Vigdor, T.G. Throwe, M.C. Green, W.W. Jacobs, R.D. Bent, J.J. Kehayias, W.K. P i t t s ,  and T.E. Ward 
Indiana Univers i ty  Cyclotron F a c i l i t y ,  Bloomington, Indiana 47405 
I n  the  process  of a t tempt ing t o  extend e a r l i e r  
measurements f o r  (p,n') ground-state t r a n s i t i o n s 1  t o  
d i f f e r e n t  mass regions ,  we have r e c e n t l y  discovered a 
s t r i k i n g  and unexpected sys temat ic  f e a t u r e  of (p ,~ ' )  
s p e c t r a  on many t a r g e t  nucle i :  a dominant f r a c t i o n  of 
t h e  t o t a l  y i e l d  t o  d i s c r e t e  s t a t e s  is o f t e n  
concentra ted  i n  one o r  a few s t a t e s  i n  a narrow region 
of e x c i t a t i o n  energy (E,). I n i t i a l  sys t ema t i c s  f o r  
t h e s e  dominant t r a n s i t i o n s  were e s t ab l i shed  by 
measuring broad-range (p,n') s p e c t r a  wi th  the  QQSP 
magnetic spect rograph f o r  bombarding ene rg ie s  i n  the  
range Ep=183-206 MeV,  us ing Di rec to r ' s  d i s c r e t i o n a r y  
beam time dur ing the  per iod when the  po la r i zed  ion  
source  was being repai red.  Representa t ive  
forward-angle s p e c t r a  f o r  s i x  t a r g e t s  a r e  shown i n  Fig. 
1. Q u a l i t a t i v e l y  s i m i l a r  concentra t ions  of s t r e n g t h  
have been observed f o r  s e v e r a l  o the r  t a r g e t s  i n  each of 
these  mass regions.  Ex f o r  the  dominant s t a t e s  v a r i e s  
slowly with mass, from - 6-7 MeV f o r  lp-shel l  t a r g e t s  t o  
-3 MeV i n  the  Z r  region. The forward-angle c ross  
s e c t i o n s  vary r ap id ly ,  but not always monotonically,  
wi th  neutron excess ,  and appear t o  be maximized when 
90 
60 
30 
90 
60 
30 
Excitation Energy (MeV) 
Figure  1. Spec t r a  f o r  
t h e  (P,R-) r e a c t i o n  on 
several targets at 
!tab=3O0 (28" f o r  t he  
C t a r g e t ) ,  showing 
s t r o n g  s e l e c t i v e  
e x c i t a t i o n  of one o r  a 
few low-lying s t a t e s .  


Measurement Near Threshold of 9-Be(3-He, Pi) to the A = 12 Isobaric Triplet by Recoil Detection

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Measurement Near Threshold of 9-Be(3-He, Pi) to the A = 12 Isobaric Triplet by Recoil Detection

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