This work was supported by National Science Foundation Grant PHY 75-00289 and Indiana Universit

Debevec, P.T.

Gutay, L.

Moake, G.L.

Quin, P.A.

Scharenberg, R.P.

English

IUScholarWorks

AN AD-HOC FACILITY FOR FORWARD ANGLE NEUTRON TIME-OF-FLIGHT EXPERIMENTS : THE 1% (p , n) 1 2 ~  REACTION 
R.P. Scharenberg*, G.L. Moake*, L. Gutay*, P.A. Quin**, and P.T. Debevec 
A temporary f a c i l i t y  f o r  neutron time-of-flight 
s tudies  i s  operational.  The beam from the  energy 
analys is  slits is transported without def lect ion 
through a shielding wall  by two quadrupole doublets 
t o  a t a rge t  placed near the  entrance of a l a rge  
dipole magnet (BNL 18 D 36). The beam spot a t  the  
t a rge t  is 1.7 mm horizontal  by 4.9 ram v e r t i c a l  
with hor izonta l  and v e r t i c a l  divergences of 3.2 m r  
and 3.8 m r ,  respectively.  The t o t a l  e f fec t ive  
path length difference due t o  the  beam l i n e  is 
achieved by a scheme of modular shielding, namely one 
foot cubes of lead on movable car ts .  The shel f  by 
which the  costs  a re  supported and the  f loor  of the  
time-of-flight path have been surveyed t o  allow 
reproducable placement of the  modular hor izonta l  
coll imation and the  detector.  With the t a rge t  a t  
the  entrance of the  dipole,  the  time-of-flight path 
is a maximum of 30 m with an angular range of -3O t o  
28O. Placement of the  t a rge t  i n  the dipole could 
double the  possible angular range. 
1.2 cm o r  about 80 ps f o r  8=0.5. After passing The detector  and its anc i l l a ry  e lect ronics  a r e  
through the  t a rge t ,  the  beam is def lected by the placed i n  a movable house. The detector consis ts  
dipole through an angle of 38O and is transported of three  parts:  a 1/4" x 10" x 20" sheet of NE102 
7.5 m t o  a Faraday cup buried in the  west wal l  of 
the  building.  Collection of multiply sca t t e red  
beam is excel lent  a s  the  acceptance of t h e  dump 
is % 5 Brms f o r  a 250 keV carbon target .  
S c i n t i l l a t o r s  monitor scat tered beam a t  5 lo0 
through 4 m i l  Kapton windows. These s c i n t i l l a t o r s  
monitor both beam spot s h i f t s ,  which a r e  
negl ig ible ,  and beam a r r i v a l  time s h i f t s ,  which 
a re  s ign i f i can t .  Neutrons pass between the pole 
faces of the  dipole and through another 4 m i l  
Kapton window. The 8" gap of the  dipole  reduces 
pole face  scat ter ing.  Ver t ica l  coll imation is 
achieved with a graduated horizontal  s l o t  i n  a 
four-foot th ick shielding wall  of s t e e l ,  lead,  and 
concrete; t h i s  s l o t  permits a remote detector t o  
view only the  t a rge t .  Horizontal coll imation is 
which serves a s  a charged-particle t r igger ,  two o r  
three  1.75" d ia  x 18" P i l o t  U rods i n  which the 
neutron i n t e r a c t s  and which a c t  i n  p a r a l l e l  t o  increase 
the  s o l i d  angle; and a 6" x 10" x 20" vat  of NE213 
which co l l ec t s  r eco i l ing  charged p a r t i c l e s  from the  
rods and permits discrimination of low energy neutrons 
from the  previous beam burs t .  The underlined dimension 
is p a r a l l e l  t o  the  en t ran t  pa r t i c l e s .  Efficiency 
ca l ib ra t ion  of t h i s  detector  with tagged neutrons 
is  planned. Calculations show the  eff ic iency t o  
be % 4%. 
The beam l i n e  appears t o  be su i t ab le  f o r  high- 
energy neutron time-of-flight s tudies .  Essent ia l ly  
no high energy neutrons a r e  detected with the  beam 
passing through a blank t a rge t  frame. In-scattering,  
determined by shadowing the  detector  from the  target ,  
is a t  about t h e  5% l e v e l .  Pulse s e l e c t i o n  a t  l / n ,  absorpt ion  model w i th  one pion exchange is under- 
where n is the  harmonic number, produces a s a t e l l i t e  way. It is hoped t h a t  t he  s t r e n g t h  of t h e  i sovec to r  
peak a t  t h e  0.01%-0.1% l e v e l .  Beam a r r i v a l  time sp in  dependent components of  t h e  e f f e c t i v e  i n t e r -  
s h i f t s  a r e  s i g n i f i c a n t ,  b u t  continuous monitoring a c t i o n  can be determined and t h e  p o s s i b i l i t y  of 
allows of f - l ine  correc t ion .  Schemes f o r  on-l ine determining the  pion-nucleus -nucleus coupling 
co r r ec t ion  a r e  under development. The f a s t e s t  cons tant  can b e  explored. 
s h i f t ,  however, is  only 10  ps / s ec  and i s  pro- 
*Purdue Univers i ty ,  Lafayet te ,  Indiana 4 7907 
bably due t o  poor magnetic f i e l d  regula t ion  of 
**University of  Wisconsin, Madison, Wisconsin 
t he  i n j e c t o r  and main s t a g e  cyclo t rons .  
Data f o r  t he  1 2 ~ ( p , n ) 1 2 ~  r eac t ion  a t  Ep=144 
MeV have been c o l l e c t e d  and a r e  under ana lys i s .  
A time-of-flight spectrum inc luding  beam a r r i v a l  
t i m e  co r r ec t ion  bu t  without  energy d iscr iminat ion  
is shown i n  Figure 1. The r e so lu t ion  he re in  is 
l imi t ed  by beam a r r i v a l  time s h i f t s .  An angular  
d i s t r i b u t i o n  (without low energy background 
subt rac ted)  is shown i n  Figure 2. The ground 
s t a t e  is forward peaked, continuing the  t rend  
evident  from i n e l a s t i c  proton s c a t t e r i n g .  
Theore t ica l  a n a l y s i s  of t h i s  angular  d i s t r i -  
but ion  i n  terms of t he  DWBA wi th  an e f f e c t i v e  
nucleon-nucleon p o t e n t i a l  and i n  terms of t h e  
Neutron Time of Flight Spectrum 
I 
' * ~ ( ~ , n )  ' 2 ~  
Ep = 144 MeV 
Cos 8 
Figure  2. 
Figure 1. 


An Ad-Hoc Facility for Forward Angle Neutron Time-of-Flight Experiments: The 12-C(p,n)12-N Reaction

https://scholarworks.iu.edu/dspace/bitstream/2022/3031/1/iucf_1976_61-62.pdf

An Ad-Hoc Facility for Forward Angle Neutron Time-of-Flight Experiments: The 12-C(p,n)12-N Reaction

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