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

Beck, D.

Cantrell, M.

Farkhondeh, M.

Holt, R.J

Low, D.

Schulze, M.

Stephenson, E.J.

Turchinetz, W.

English

IUScholarWorks

DEVELOPMENT OF POLARIMETEKS AND DETECTORS 
SEARCH FOR A T20 ANALYZER FOR DEUTERONS 
E. J. Stephenson, M. Cantrell, and D. Low 
Indiana University Cyclotron Facility, Bloomington, Indiana 47405 
R.J. Holt 
Argonne National Laboratory, Argonne, Illinois 60439 
D. Beck, M. Farkhondeh, M. Schulze, and W. Turchinetz 
Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 
In this experiment we surveyed the cross section scattering experiments are just beginning at MIT, and 
and T20 analyzing power for several deuteron-induced will provide the first separation of the charge and 
reactions, looking for a case where the cross section quadrupole form factors of the deuteron. In order to 
and analyzing power are large and could be used to continue the electron scattering studies to higher 
construct a polarimeter for intermediate-energy momentum transfer, a polarimeter of greater efficiency 
tensor-polarized deuterons. Such a polarimeter would is needed for deuterons in the range near 100 MeV. 
find immediate use in double scattering experiments, To complement other experiments at IUCF, this 
measuring the recoil deuteron polarization from pion or survey examined five targets with 80-MeV polarized 
electron elastic scattering. Such double scattering deuterons. The measured cross sections and T20 tensor 
experiments are the only method available for examining analyzing powers were used to estimate the figure of 
tensor observables in these systems, since a tensor merit of a polarimeter based on each observed reaction. 
polarized deuterium target is not presently feasible. The- figure of merit, Q = JZ 1 ~ ~ ~ 1 ,  is inversely 
A high-efficiency polarimeter for lower energy proportional to the statistical errors generated in an 
deuterons already exists. Its analyzer is the experiment using such a polarimeter. The present low 
3~e(d,p)4~e reaction, which has a negative maximum in energy design5 has Q = 8.6~10'~. 
T20 near 6 MeV. This polarimeter consists of front To make a useful polarimeter, it is also important 
scintillation counters to monitor the deuteron flux, a that the reaction products must be easily observable in 
high pressure 3 ~ e  cell, and rear scintillation counters 
to identify protons emitted near 0". Because of the 
energy loss in the front counters, its operating range 
is from 20 to 27 MeV. The operating efficiency, or 
ratio EO of detected protons to incident deuterons, is 
1.2~10'~ with a tensor analyzing power of about 
T20 = -0.75. 
This polarimeter, and another like it, have been 
used in elastic pion-deuteron scattering experiments at 
LAMPF~, and  SIN^, 5. These data have been used to 
a simple geometry, as well as possess a high figure of 
merit. 
At 80-MeV, angular distributions of T20 exist only 
for elastic scattering6 from 58~i. This angular 
distribution has T20 values near zero at forward 
angles, and values decreasing slowly to -0.2 at angles 
larger than 70". At large angles the scattering cross 
section is small, and a polarimeter based on such 
scattering can provide only Q = 2x10'~. The values of 
T20 for elastic scattering from medium to heavy weight 
study true pion absorption. Elastic electron targets originates from the spin-orbit interaction, and 
so  we expect the  same analyzing power t o  apply t o  a l l  
r eac t ion  channels. Thus s i g n i f i c a n t l y  d i f f e r e n t  
r e s u l t s  can only be expected from the  very l i g h t e s t  
t a rge t s .  Because the re  a r e  fewer open reac t ion  
channels on l i g h t  t a r g e t s ,  each d i s c r e t e  f i n a l  s t a t e  
has a l a r g e r  c ross  sec t ion ,  and the re  may be r eac t ions  
[such a s  6 ~ i ( d , a ) a ]  t h a t ,  f o r  s t r u c t u r e  reasons, have 
l a r g e  values of T20. Thus we chose t o  i n v e s t i g a t e  3 ~ e ,  
6 9 7 ~ i ,  9 ~ e ,  and 12c. 
At lower ene rg ies ,  a l a r g e  negat ive  excursion i n  
T20 has been repor ted f o r  deuteron-proton s c a t t e r i n g  
near 0 = 120°. This excursion g e t s  l a r g e r  a s  the  
bombarding energy increases .  A rough ca lcu la t ion  shows 
t h a t  a polar imeter  based on t h i s  case would have Q = 
9x10'~. Time did  not permit us t o  extend these  
measurements t o  higher  energy. 
Measurements of T20 with  the  IUCF polar ized 
deuteron beam requ i re  the  measurement of the tensor  
analyzing power i n  both the  hor i zon ta l  ( t o  ge t  Ayy) and 
v e r t i c a l  ( t o  ge t  &) planes. This was c a r r i e d  out 
wi th  the  new r o t a t i n g  s c a t t e r i n g  t a b l e  mounted i n  the  
y-cave. The s o l i d  carbon and beryllium t a r g e t s  were 
mounted i n  a i r ,  t he  l i th ium t a r g e t s  were mounted i n  an 
evacuated gas c e l l ,  and the  helium gas was contained i n  
t h e  same gas c e l l .  The d e t e c t o r  te lescopes  consis ted 
of 1 mn S i  d e t e c t o r s  backed by 15 m Ge de tec to r s .  
There was no a c t i v e  col l imat ion,  so we expected t h a t  
t h e  higher e x c i t a t i o n  regions  of the  spec t ra  would 
con ta in  ghost f ea tu res .  This scheme was considered 
s a t i s f a c t o r y  s ince  any use fu l  r eac t ion  must come from a 
s t rong ,  e n e r g e t i c  group. A polar imeter  based on 
reac t ions  i n t o  the  continuum was considered an un l ike ly  
prospect.  The measurements were made with 78.9 MeV 
polar ized deuterons, and concentrated a t  forward 
s c a t t e r i n g  angles.  The measurements of kjy and & 
were combined t o  form T20 according t o  
The c ross  sec t ion  was measured i n  both o r i en ta t ions .  
I n  general ,  t he  r eac t ion  c ross  sec t ion  was 
dominated by deuteron e l a s t i c  s c a t t e r i n g  and protons 
from deuteron breakup. Sample s p e c t r a  a r e  shown i n  
Fig. 1. The T20 analyzing power f o r  deuteron breakup 
was c lose  t o  zero f o r  a l l  angles  and t a rge t s .  For 
deuteron e l a s t i c  s c a t t e r i n g  and i n e l a s t i c  s c a t t e r i n g  t o  
t h e  f i r s t  few d i s c r e t e  s t a t e s ,  T20 was near zero a t  
forward angles  and f e l l  t o  -0.4 a t  60'. Because of t h e  
appearance of negat ive  analyzing powers a t  angles  
more forward than previously  observed f o r  5 8 ~ i ,  a
DEUTERON 
J 500 - 
W 
z 
z 
a 
I 
t! 
V) 
t- 
3 o I 1 I 
8 
3001 PROTON 
0 160 2 b  360 
CHANNEL 
Figure 1. Sample spec t ra  from deuteron-induced 
reac t ions  on 9 ~ e ,  observed a s  inc lus ive  s p e c t r a  f o r  
deuterons and protons a t  30'. A contaminant from air 
and a ghost of the  e l a s t i c  peak a r e  v i s i b l e  i n  t h e  
deuteron spectrum. 
polar imeter  based on t h i s  e f f e c t  would achieve 
Q = 6 ~ 1 0 - ~  us ing a 1 2 C  t a rge t .  
There were few reac t ions  wi th  l a r g e  enough c ross  
s e c t i o n  and T20 analyzing power t o  be considered f o r  a 
polar imeter .  The T20 angular  d i s t r i b u t i o n  f o r  t he  
3 ~ e ( d , p ) 4 ~ e  r a c t i o n  o s c i l l a t e s  about zero  a t  80 MeV, 
and a simple polar imeter  de t ec t ion  geometry d id  not 
seem poss ible .  The 6 ~ i ( d ,  a ) a  r e a c t i o n  c a r r i e d  the  
l a r g e s t  analyzing power, namely T20 = -0.92 a t  lo0. 
But a small  c ross  s e c t i o n  (< 100 pb/sr )  l i m i t s  t h i s  
analyzer  t o  Q = 3x10'~. 
The t enso r  analyzing powers we measured a l l  obeyed 
t h e  empi r i ca l  r e l a t i o n  
Assuming t h a t  most polar imeters  would u s e f u l l y  span a 
s o l i d  angle  of 1 sr and would have t a r g e t s  t h i c k  enough 
t o  s t o p  100 MeV deuterons  (about 5 g/cm2), then the  
f i g u r e  of merit has a upper l i m i t  given by 
where A is the  t a r g e t  mass. This r e l a t i o n  is sketched 
i n  Fig. 2, along wi th  the  f i g u r e s  of mer i t  f o r  t he  
po la r ime te r s  we considered poss ible .  
PRESENT 
a 
Y 
LL 
'SYSTEMATIC' 
UPPER LlWT 
W 
0 10 
- .  
58 
TARGET MASS 
Unlike the  exper ience  wi th  vec to r  p o l a r i z a t i o n ,  the  
p o t e n t i a l s  l ead ing  t o  s i g n i f i c a n t  t enso r  analyzing 
powers a r e  not  A-dependent, and do not g ive  l a r g e r  
e f f e c t s  with inc reas ing  bombarding energy. I n  f a c t ,  
t he  o r i g i n  of a s i g n i f i c a n t  f r a c t i o n  of the  tensor  
analyzing powers near  100 MeV becomes the  second-order 
sp in -o rb i t  po ten t i a l .  Thus we can f i n d  no case  i n  the  
pe r iod ic  t a b l e  where t h e r e  is a r e a c t i o n  t h a t  would 
y i e l d  a polar imeter  wi th  a s i g n i f i c a n t l y  h igher  value 
of Q than the  one p resen t ly  i n  use. The bes t  prospect  
f o r  a t a r g e t ,  e s p e c i a l l y  a t  even higher bombarding 
ene rg ie s ,  appears t o  be hydrogen. 
1. R. J. Holt ,  J.R. Specht, E.J. Stephenson, B. 
Zeidman, R.L. Burman, J.S. Frank, M.J. Lei tch ,  J. 
D. Moses, M.A. Yates-Williams, R.M. Laszewski, and 
R.P. Redwine, Phys. Rev. Let t .  43, 1229 (1979). 
2. R.J. Holt ,  J.R. Specht, K. Stephenson, B. Zeidman, 
J.S. Frank, M. J. Lei tch ,  J.D. Moses, E. J. 
Stephenson, and R.M. Laszewski, Phys. Rev. Let t .  
47, 472 (1981). 
-
3. J. Ulbr icht ,  V. Konig, W. Gruebler,  P.A. 
Schmelzbach, B. Jenny, F. Sper isen,  K. Elsener ,  C. 
Schweizer, and A. Chisholm, Phys. Rev. Let t .  48, 
311 (1982). 
4. W. Gruebler,  J. Ulbr icht ,  V. Konig, P.A. 
Schmelzbach, K. Elsener  , C. Schweizer , M. Merdzan, 
and A. Chisholm, Phys. Rev. Let t .  3, 444 (1982). 
5. E. J. Stephenson, R. J. Holt ,  J.R. Specht, J.D. 
Moses, B.L. Burman, G.D. Crocker, J.S. Frank, M.J. 
Lei tch ,  and R.M. Laszewski, Nucl. Instrum. and 
Meth. 178, 345 (1980). 
6. E.J. Stephenson, p r i v a t e  communication. 
7. V. Konig, W. Gruebler,  R.E. White, P.A. 
Schmelzbach, B. Jenny, F. Sper isen,  C. Schweizer, 
and P. Doleschal l ,  F i f t h  In t .  Symp. on P o l a r i z a t i o n  
Phenomena i n  Nuclear Reactions,  eds. G.G. Ohlsen, 
Ronald E. Brown, Nelson J a m i e ,  W.W. McNaughton. 
and G.M. Hale (AIP Conf. Proc. - No. 69, ~ e w - ~ o r k ;  
1981) p. 1208. 
Figure  2. The sys t ema t i c  upper l i m i t  on the  f i g u r e  of 
mer i t  (defined i n  the  t e x t )  f o r  any T20 polar imeter .  
The f i g u r e  of mer i t  f o r  any polar imeters  based on 
r e a c t i o n s  observed i n  t h i s  experiment a r e  ind ica t ed  a s  
d o t s  o r  arrows. The des ign f o r  a hydrogen t a r g e t  is 
based on the  d a t a  of Ref. 7. 


Search for a T_20 Analyzer for Deuterons

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Search for a T_20 Analyzer for Deuterons

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