Transcript A Polarized 3He Target System for Low

3He
Polarized
Target for Low-Energy
Charged Particle Scattering Experiments
1 B
10 3

B x
cm
a,b,
a,b,
a,b
a,b,
T. Katabuchi
M. S. Boswell
T. B. Clegg , T. V. Daniels
a,b
a,b
c
a,b
M. Fassler , B. M. Fisher , S. Kadlecek , H. J. Karwowski ,
a,b
a,b
c
a,b
D. S. Leonard , E. J. Ludwig , J. Nouls , and W. Weinzierl
a,
Triangle Universities Nuclear Laboratory University of North Carolina
c
Amersham Health
TUNL Polarized
Motivation and Goal
3He(p,p)
3He
b,
Target System
• Target cell inside sine-theta coil
at low energies
• 3He polarization monitored with NMR
• Mass-3 System
– A 3-nucleon force is needed to predict 3H and 3He
binding energies
• Separate optical pumping station
• 3He to be polarized by Rb spin exchange
– Ay disagrees with theoretical predictions (Ay puzzle)
p + 3He
Ecm = 1.69 MeV
• Mass-4 System
– Effort is turning to 4-nucleon-system where
p-wave resonant states exist at very low energies.
Target Cell
• Pyrex: easy to fabricate
• Capillary feed for 3He
• Kapton Beam entrance and exit
• Side apertures for emerging particles
• Ay Puzzle
– Recent theoretical effort shows that the “Ay Puzzle”
persists
Target Cell (1 atm)
Sine-Theta Coil
67 cm
NMR Coil
– Effects are larger in mass-4 than in the mass-3
system.
Glass Cell
Beam
23 cm
7G
• New data needed
– New spin-dependent data are sought below Ep = 6
MeV to resolve theoretical ambiguities.
3
H
e
NMR Pickup Coil
Scattering Chamber
– Aoy and Ayy are the first objective.
Optical Pumping Station
Kapton Window
Sine-Theta Coil
0
• Highly uniform B-field required
over target volume
Outward
Inward

• Required field uniformity
B
– Current I  sin 
• For 3He(a,3He)4He, Ay = 1 at lab=47°,
Elab=15.33 MeV (G.R.Plattner and A.D.Bacher,
(1971))
m-metal cylinder
Results
• Variable surface current
– Enhances B-field inside
cylinder
0
Mu-metal Shield
• Spin relaxation time acceptable for later
experiment ~ 3 hours
1/8" Copper Rods
– Shields internal region from
external fields.
12" (30 cm)
•NMR secondary polarimetry standard known
to ±2 %
3 1/8 " (8 cm)
Windows
Measurement of B-Field
Summary
• Currents adjusted to provide Bx = 10 Gauss
Results
• Scanned interior with a 3-axis Hall probe
Mu Metal Shield
3
1 B
10
 < 2 x 10-3/cm
• Found
B x
cm
1 B
10 3
• Sine-Theta Coil –
< 2 x 10B x
cm
3
Transverse-component midplane contour maps (in Gauss)
x
• Pyrex Cell – T1> 3 hrs
By
Bz
/cm
• NMR polarimetry calibrated with
3He(a,3He)4He scattering
Future Plan
• Storage cell and optical pumping
system under construction
y
z
• Mapping of Ay of 3He(a,3He)4He to
find the exact point where Ay=1
• Scattering experiments for A0y and
Ayy
He Polarization
Max
0.5
500
0.4
400
0.3
300
0.2
200
3
Max
• Alpha particle elastic scattering used to
calibrate NMR polarimetry
NMR signal
3
He(a,3He)4He
0.1
0
20
40
60
Time (min)
80
100
100
NMR signal (mV)
Polarization Calibration Experiment
1 B
1
-1

cm
B x 1000
•
Results of First Experiment with beam