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

Bonner, B.E.

Buchanan, J.A.

Clement, J.M.

Foster, C.C.

Phillips, G.C.

Ratner, L.G.

Rice, J.A.

Roberts, J.B.

von Witsch, W.

English

IUScholarWorks

ABSOLUTE CALIBRATION OF A 200 MeV PROTON POLARIMETER FOR USE WITH THE BROOKHAVEN LINAC 
J.B. Roberts, J.A. Buchanan, J.M. Clement, G.C. P h i l l i p s ,  J.A. Rice, and W. von Witsch 
Bonner Nuclear Laboratory, Rice University, Houston, Texas 77001 
B.E. Bonner 
Los Alamos National Laboratory, Los Alamos, New Mexico 87545 
L.G. Ratner 
Brookhaven National Laboratory, Upton Long Is land,  New York 11973 
C.C. Foster 
Indiana University Cyclotron F a c i l i t y ,  Bloomington, Indiana 47405 
Construction of the polarimeter fo r  use with the bias ,  was used t o  normalize the s c a t t e r i n g  r a t e s  over 
Brookhaven National Laboratory 200 MeV LINAC polarized beam f l u x  var ia t ions.  The f i n a l  voltage of each of the 
beam has been completed. The instrument was t es ted  and RCA 8575 tubes was s e t  150 V above the onset voltage of 
ca l ib ra ted  during December 1982 a t  the Indiana the counting-rate plateau t o  ensure e f f i c i e n t  counting. 
University Cyclotron Fac i l i ty .  The instrumental asymmetry was then measured a s  a 
The polarimeter was ca l ib ra ted  with unpolarized funct ion of t a rge t  posi t ion,  where the asymmetry is  
and polarized beams of 200-MeV protons a t  the Indiana defined as: 
University Cyclotron Fac i l i ty .  A 0.010" x 0.020" (NL-NR) / ( NL+NR), 
carbon filament t a rge t  sca t t e red  the protons t o  (see Fig. 2). The instrumental asymmetries a r e  0.017 
s c i n t i l l a t o r  telescopes a t  12 and 16 degrees i n  the f o r  the 12 degree angle and 0.006 f o r  the 16 degree 
horizontal  plane and 16 degrees i n  the v e r t i c a l  plane. angle with the t a rge t  a t  the optically-surveyed 
The ta rge t  design (see Fig. lb )  allows three d i f f e r e n t  pos i t ion  of the polarimeter axis.  These small 
carbon t a r g e t s  t o  be placed on instrument center  t o  an instrumental asymmetries can be accounted f o r  due t o  
accuracy of 0.001 inch or  t o  be removed from the beam. small e r r o r s  i n  fabr ica t ions  of the small p l a s t i c  
The t a rge t s  a re  machined graphi te  ribbons of var iable  s c i n t i l l a t o r s  and small e r r o r s  i n  the 12 degree 
horizontal  width W, v e r t i c a l  height H, and var iable  s e t t i n g s  . 
thickness T along the beam direct ion.  The design is Using a 75% polarized beam, the analyzing power of 
such t h a t  H >> height of beam spot ,  W << width of beam carbon s c a t t e r i n g  f o r  the polarized beam was measured 
spot ,  and T can be chosen t o  obtain s u i t a b l e  count t o  be 0.620+.004 a t  12 degrees and 0.511+.004 a t  16 
ra tes .  By choosing W, the destruct ion of the beam degrees. In  addi t ion,  the analyzing power was s tudied 
(H' s t r ipped  t o  H+) can be kept t o  a few percent. The a s  a funct ion of copper absorber thickness placed j u s t  
analyzing power of the carbon ta rge t  was determined a t  before the second de tec to r  i n  each telescope. The 
12 and 16 degrees, and as  a function of ranging analyzing power was enhanced by ranging out the 
mater ia ls  i n  an attempt t o  maximize the eff ic iency.  ine las t i ca l ly - sca t t e red  p a r t i c l e s ,  (see Fig. 3). Of 
I n i t i a l l y ,  with unpolarized beam, all course, as the amount of copper absorber was increased 
photomultiplier tubes were individual ly  monitored f o r  t o  enhance the analyzing power A, the  counting r a t e s  
counting r a t e  as  a funct ion of the voltage across t h a t  decreased, (see Fig. 4). Counting r a t e s  were measured 
tube. A s c i n t i l l a t o r  telescope, maintained a t  f ixed f o r  symmetrically positioned telescopes. I n  Fig. 4, 
TARGET 
ACTUATOR 
Figure  1. Schematic diagram of the  200 MeV proton polar imeter  f o r  use  with the  Brookhaven LINAC. Figure  l a  is a 
p lan view. Figure  l b  view from the  upstream d i r e c t i o n  of beam t r a v e l .  
F igure  2. Ins t rumental  asymmetry a s  a func t ion  of 
target p o s i t i o n  f o r  d e t e c t o r s  a t  f12O and 16O. 
Figure  3. Analyzing power versus  th ickness  of copper 
absorber  placed between the  polar imeter  t a r g e t  and t h e  
+12O de tec to r s .  As more e n e r g e t i c  protons a r e  stopped 
i n  the  s i d e  counter  t he  average analyzing power 
increases .  
t he  12 degree h o r i z o n t a l  te lescopes  counts,  with added 
absorber ,  a r e  denoted a s  NL and NR ( f o r  l e f t  and r i g h t )  
and a r e  compared t o  the  12 degree up and down 
t e l e scopes  wi th  no absorber.  To optimize the  
po la r ime te r ' s  measurement e f f i c i e n c y ,  a q u a l i t y  f a c t o r  
was defined. Since the  e r r o r  i n  the  measured 
p o l a r i z a t i o n ,  P is: 
- P * A ~  1/2  
' P =  + ( ' N L + N R  1 
Coincidences at 12 Degrees 
t h e  q u a l i t y  f a c t o r  t o  be maximized is  then ~~daIdC-2 (see  
Fig. 5). A maximum q u a l i t y  f a c t o r  of 127 mb/sr is  
obtained f o r  0.650 cm of copper absorber  placed 
immediately upstream of the  12 degree t e l e scopes  ' 
downstream s c i n t i l l a t o r s ;  however, t he  v a r i a t i o n  versus  
absorber  is small .  At the  conclus ion of these  t e s t s  
t he  hardware was taken t o  Brookhaven National 
Laboratory and l e f t  t h e r e  f o r  l a t e r  i n s t a l l a t i o n  and 
i n t e g r a t i o n  i n t o  the  AGS computer system. 
Copper Absorber Thickness (cm 1 
Figure  5. P lo t  of polar imeter  q u a l i t y  f a c t o r  versus  
Firrure 4. Ra t io  of summed counts i n  the  212" counter  copper absorber  th ickness .  
V
t o  summed counts i n  t h e  216" up-down counters  a 
func t ion  of copper absorper  th ickness  f r o n t  of t he  
s i d e  counters  only. Count r a t e s  i n  the  s i d e  counter  
f a l l  wi th  inc reas ing  th ickness .  


Absolute Calibration of a 200 MeV Proton Polarimeter for Use with the Brookhaven Linac

https://scholarworks.iu.edu/dspace/bitstream/2022/2739/1/iucf_1982_166-168.pdf

Absolute Calibration of a 200 MeV Proton Polarimeter for Use with the Brookhaven Linac

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