This research was sponsored by the National Science Foundation Grant NSF PHY-931478

Berg, G.

Blomgren, J.

Cameron, J.

Jourdan, F.

Miller, D.

Ni, B.

Rinckel, T.

Saber, M.

Spraker, M.

Wang, Y.

English

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BREAKUP REACTIONS 
MEASUREMENTS OF THE PROTON-NEUTRON CORRELATION 
IN DEUTERON BREAKUP AT 260 MEV 
G. Berg, J .  Blomgren, J .  Cameron, F. Jourdan, D. Miller, 
B. Ni, T. Rinckel, M. Saber, M. Spraker and Y. Wang 
I n d i a n a  Univers i ty  Cyc lo t ron  Facili ty,  B loomington ,  I n d i a n a  4 74 08 
Experiment CElO was designed to study the proton-neutron correlation from deuteron 
breakup in order to provide important information, such as the possible intensity and 
energy resolution of a tagged, polarized neutron beam with good resolution created by 
the breakup of polarized deuterons in the cooler ring. Studies of the interference between 
Fermi and Gamow-Teller transition amplitudes by the (I?, p) reaction on a light polarized 
target, and of the isovector term in the nucleon-nucleus interaction by measurement of 
cross sections and analyzing powers in neutron scattering on nuclei with a neutron excess, 
would be important sample experiments utilizing such a beam.' 
The experiment was divided into two parts. The first part, done in the T-region of 
the Cooler ring in February 1992, was to study the angular correlation of the two breakup 
nucleons in a small angular range. The second part, done in the G-region in March 1992, 
measured energies of the two nucleons with a detection system intended to provide about 
400 keV resolution. 
Angu lar  Corre la t ion  Measuremen t s  
In this part of the experiment, the angular correlation of neutrons and protons from 
the C(d,np), Cu(d,np) and Pb(d,np) reactions were measured in the horizontal angular 
ranges of 0" < Op 5 6" and 0" 2 8, 2 -6" (on the opposite side of the beam). A stored 
beam of 260-MeV deuterons with an intensity of about 90 ,uA and a cycle period of 45 
s was used with the data-taking time in each cycle being 25 s. Three "skimmer" targets 
were made from natural C, Cu and Pb, with thicknesses of 650 mg/cm2, 680 mg/cm2, and 
2400 mg/cm2 respectively. 
A proton telescope, consisting of a delay-line wire chamber with both x and y wire 
planes sandwiched between a pair of 0.3 cm-thick scintillators and followed by two 8.3 cm- 
thick NaI(T1) detectors, was located downstream from the T-region 6" magnet. The dis- 
tance between the target and the wire chamber was 124 cm, and the spacing between 
two adjacent anode wires in each wire plane was 4 mm. The telescope covered breakup 
protons from nearly Bp = 0" to Bp = 6" with vertical acceptance of about A$, = 3". Elas- 
tic deuteron scattering events, used as the luminosity monitor for the experiment, were 
also detected with the same telescope. The horizontal acceptance for these deuterons was 
4.5" < Bd < 10.5". While breakup protons were stopped in the first NaI(T1) detector, the 
elastically-scattered deuterons passed through it and were stopped in the second NaI(T1). 
Gain matching of the two NaI(T1) detectors was obtained by degrading the energy of the 
elastically-scattered deuterons with absorbers of different thicknesses placed in front of one 
NaI(T1) with the other taken away. 
Neutrons were detected with an array of 102 cm x 15 cm x 10 cm plastic scintillator 
bars placed on the opposite side of the beam pipe from the proton telescope, and about 
9.5 m away from the target with the long side parallel to the breakup neutrons. They 
were arranged so that each one measured neutrons of a particular scattering angle 8, 
with a horizontal acceptance of Ad, = 0.67" and a vertical acceptance of A$, = 1". By 
measuring timing at both ends of each scintillator, the position at which (n,p) conversion 
occurred could be determined with an accuracy of about 3.5 cm (out of 102 ~ m ) . ~  In 
order to measure the efficiency of each scintillator, one identical scintillator was placed 
in front of these scintillators with its 102 cm x 15 cm side facing the target and 8.1 m 
away. Placed in this way, the efficiency of this "front" scintillator was known based on 
previous measurements; by comparing its yield with that of the "rear" scintillators, one 
can estimate the efficiency of each scintillator. Charged-particle veto was provided by a 
thin scintillator pad in front of all the above detectors. 
A neutron signal was defined by a hit in any one of the scintillator bars with charged- 
particle veto. The coincidence of this signal with both scintillators in the proton telescope 
triggered (d,np) events, and the time of flight (TOF) of neutrons were measured with a 
"start" from the proton telescope. Triple coincidence of both scintillators and the second 
NaI in the proton telescope, vetoed by the neutron signal, triggered (d,d) events which 
(prescaled by a factor of 10) were simultaneously taken with the (d,np) events. 
Several short runs were taken to measure (d,d) and inclusive (d,px) events simultane- 
ously. Coincidence of the two scintillators in the proton telescope triggered both events, 
and separation of deuterons and protons was done in software. In addition to measur- 
ing the cross section angular distribution for (d,px), these runs also helped to determine 
accidental backgrounds in (d,np) events. 
Data analysis is in progress which includes: calibrate NaI(T1) detectors to get Ep 
and Ed; extract position Zp (Zd) relative to the target when p(d) hits the wire chamber; 
calculate Bp (Bd) using ray-trace from Ep (Ed), jip (Zd), and the field map of the 6" 
magnet; calculate solid angles of p(d) at each scattering angle using ray-trace; calibrate 
neutron TOF to get En; subtract accidental background; estimate efficiency of the neutron 
detectors; calculate luminosity using (d,d) yield and optical potential calculations; and 
estimate systematic errors. 
Some preliminary results are shown in Fig. 1-3. The angular distribution of the 
deuteron yield for C(d,d) is shown in Fig. 1. Figure 2 plots the proton energy versus 
neutron energy for C(d,np). The angular correlation for C(d,np), plotted as the proton 
angular distributions for specific coincident neutron angles, is shown in Fig. 3. The error 
bars shown in all figures are purely statistical. 
1000 
4 6 8 10 
8," (lab) 
Figure 1. Measured angular distribution of C(d,d) elastic scattering at 260 MeV. 
180 . . a .  :....:.:.:.I: . . .  .; I :  . :. : ... . I  . . . . . .  . . . . . .  . . .  . . .  I . .  . I 
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Figure 2. Energy correlations for C(d,np) deuteron breakup at 260 MeV. 
Figure 9. Angular correlations for C(d,np) deuteron breakup at 260 MeV. 
Energy-Resolu t ion  Measuremen t s  
A detection system, designed to be able to measure energies of the protons (neutrons) 
with energy resolution about 200 keV (400 keV), is shown in Fig. 4. It consisted of two 
identical arms which were placed at the opposite sides of the beam pipe downstream from 
the target box in the G-region of the Cooler ring. Each arm consisted of a 0.5 mm-thick 
Si strip detector, a 3 mm-thick "front" scintillator, a multiwire four-plane drift chamber, a 
stack of intrinsic Ge detectors of total thickness of 3 cm, a 3 mm-thick "back" scintillator, 
and a 7.62 cm-thick NaI(T1) detector. A 200-MeV, 100-pA stored deuteron beam and a 
0.3 mm-thick Pb skimmer target were used during the experiment. The protons emitted 
at lab angles of 3.5" to 5.5" (or -3.5" to -5.5") and neutrons at lab angles of -3.5" to 
-5.5" (or 3.5" to 5.5") were detected in coincidence. 
The breakup protons were stopped in Ge, and their energies Ep were obtained from 
measuring the pulse height from the Ge with an expected resolution of about 200 keV. 
The breakup neutrons were converted to protons in the front scintillators through (n,p) 
reactions with a conversion efficiency of about The angles between the converted 
beam 
- 
Figure 4. Schematic drawing of the detection system in the (d,np) energy resolution 
measurement. 
G-Region 
Target Box 
protons and the neutrons, Bnp, were measured with a resolution of about lo using the drift 
chambers. BnP and Ep were then used to calculate the energies of the breakup neutrons. 
The coincidence of the two front scintillators gave hardware triggers of the (d,np) 
events. Since the (n,p) conversion efficiency was very small, (d,pp) events may have a 
comparable rate with the (d,np) trigger. Thus the Si detectors were used, in software, to 
distinguish between (d,np) events and (d,pp) events. The coincidence of the front and back 
scintillators in the same arm triggered the deuteron elastic scattering events which were 
used as the luminosity monitor for the experiment. The elastically-scat t ered deuterons 
were stopped in one of the NaI detectors. 
Problems were encountered during the experiment due to the limited lifetime of the 
Ge detectors in the high radiation field. Several detector changes were necessary. Data 
analysis for this experiment will start after the angular correlation analysis is finished. 
Front Drift 
Scin. Chamber Back 
sc;fL, 
1. IUCF Proposal to NSF: "Chicane/Spectrometer System for the IUCF Cooler Ring," 
submitted April 24, 1992. 
2. W. Huang et  al., IUCF Sci. and Tech. Rep., May 1988 - April 1989, p. 100. 


Measurements of the Proton-Neutron Correlation in Deuteron Breakup at 260 MeV

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Measurements of the Proton-Neutron Correlation in Deuteron Breakup at 260 MeV

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