Transcript Development of the Polarized 3 He Target at RCNP

Development of a Polarized
3He Target at RCNP
Youhei Shimizu
RCNP, Osaka University
Collaborators
RCNP, Osaka University :
Y. Shimizu, K. Hatanaka, Y. Sakemi, A. Tamii, H.P. Yoshida,
M. Uchida, Y. Shimbara, K. Fujita, Y. Tameshige, H. Matsubara
CNS, University of Tokyo :
T. Uesaka, T. Wakui, T. Kawabata, K. Suda, Y. Sasamoto
Saitama University :
K. Itoh
Kyushu University :
K. Sagara, T. Wakasa, T. Kudoh, M. Tomiyama, H. Ohira
Osaka University :
T. Adachi
Tohoku University :
H. Okamura
RIKEN :
H. Ueno
Bogoloyubov Institute for Theoretical Physics :
A.P. Kobushkin
Contents
1. Introduction
1.1. 3He Target
1.2. Elastic Backward Scattering
2. Polarized 3He Target at RCNP
2.1. Target apparatuses
2.2. Measurement of 3He density
3. Measurement of 3He Polarization
3.1. AFP-NMR Method
3.2. 3He(p,p+)4He Reaction
3.3. Absolute 3He Polarization
4. Summary
3He
Target
• The relative strength of target-related spin dependent
effects is larger than for any other dense nuclei.
Elastic pion scattering
p+ + 3He Tp=100MeV
p+ + 13C Tp=132MeV
p+ + 15N Tp=164MeV
B. Larson et al., PRL 67, 3356 (1991).
Yi-Fen Yen et al., PRL 66, 1959 (1991).
R. Tacik et al., PRL 63, 1784 (1989).
• The precise 3He ground state wave function is obtained by
Faddeev calculation.
• High density and the high degree of polarization.
p+3He Elastic Scattering



The cross section at back angles show a rising
pattern which is energy dependent.
In order to reproduce the ds/dW at backward angles,
deuteron exchange effects were taken into account.
There are discrepancies between the experimental
data and theoretical predictions including exchange
effects at back angles.
M.S. Abdelmonem and H.S. Sherif, PRC 36, 1900 (1987).
Elastic Backward Scattering (EBS)
Structure of the light nuclei (d, 3He, a) at short distances between the
constituent nucleons.
 High momentum components of the target wave function.
 Systematic study of the reaction mechanisms including exchange effects.
 The spin observables can give an additional information.

We developed a thick and highly polarized 3He target at RCNP.
Polarized 3He Target
• Meta-stability exchange method
1) 23S1 meta-stable 3He atoms are directly polarized by an
optical pumping method (l = 1.084 mm).
2) The polarization of the meta-stable state is transferred to
the ground state via the meta-stability exchange reaction.
• Spin-exchange method
1) Rb vapor is polarized by optical pumping with a circularly
polarized light (l = 794.7 nm).
2) The Rb electron polarization is transferred to the 3He
nucleus via the spin-exchange collision.
Easily application for high density target
Spin-Exchange Method

Rb vapor is polarized by optical pumping with a circularly
polarized light (l = 794.7 nm).
collisional mixing
52P1/2
Rb Polarization
Optical

Pumping s
radiationless
quenching from N2
opt
52S1/2

Spin Relaxation
mi =  12
SD
mi = 12
The Rb electron polarization is transferred to the 3He nucleus via
the spin-exchange collision.
Spin Exchange
e
e
3He
Rb
Hyperfine
Interaction
3He
Polarization
SE
3He
Rb
Spin Relaxation
3He

The Schematic view of the Polarized 3He Target
COHERENT FAP-79-30C-800LB
Diode Laser
Power : 60 W
Wavelength : 795 nm
Temperature Dependence of the Wavelength
 The center of wavelength is dependent on
temperature and current.
 It was necessary to lock onto the Rb D1
resonance line.
 In order to adjust the wavelength to the Rb D1
resonance line, the laser diode is cooled down to
22.3 oC by using PID (Proportional, Integral, and
Differential) feedback control.
PID Feedback Control System
 Peltier elements
 Temperature sensors (LM335)
 CC power supplier for peltier elements
We have succeeded to stabilize
the temperature within 0.1 oC.
Target Cell
 The cell had a thin window of 100 mm to reduced background from glass.
 A cell is double cell structure and consists of two parts, a target cell and a pumping cell,
connected by a transfer tube.
 Each cell volume was measured by Archimedes principle.
 The borosilicate glass, Corning7056, was used.
Type1
Type2
100 mm
50 mm
50 mm
100 mm
Target Cell
Target Cell
Thin window
of 0.1 mm
Pumping Cell
70 mm
1 : 20 hours
VT : 227 cm3
VP : 120 cm3
60 mm
30 mm
Thin window
of 0.4 mm
Pumping Cell
70 mm
1 : 15 hours
VT : 224 cm3
VP : 286 cm3
The Measurement of 3He Density
 In order to obtain the cross section and
the absolute 3He polarization, it is
necessary to know the density of the 3He
in the cells and its error.
 The 3He density of our cells was
measured by using the broadening of the
Rb resonance absorption lines by 3He
density in same manner as
Romalis et al., PRA 56, 4569 (1997).
Setup of an optical measurement
Results
The absorption width and 3He densities at
thermal equilibrium.
Absorption
width (GHz)
Density
(amgat)
Type1
60.1±0.1
3.57±0.08
Type2
62.9±0.4
3.65±0.07
Measurement of the 3He Polarization
• AFP (Adiabatic Fast Passage) - NMR
 3He polarization was monitored by AFP-NMP method.
 NMR signal is proportional to the degree of
polarization.
 The 3He polarization saturates after 1 day pumping
 AFP-NMR method only gives relative values.
 Absolute polarization must be calibrated.
Typical NMR signal
• 3He(p,p+)4He
In the case 1/2+ + 1/2+  0+ + 0, one can
show from the parity conservation that the
spin correlation parameter Cyy takes the
constant value of 1.
Time development of NMR signal
Experimental Setup
• Measurement
 3He(p,p+)4He
reaction at 0 degree
• Observables
Differential Cross section ds/dW
 3He Polarization

• Polarized proton beam



Energy:
400, 300 MeV
Polarization: 70 %
Intensity:
10 – 40 nA
Grand Raiden
• Polarized 3He gas target

Spin exchange type
 Polarization: 12 % in average
 Both cells (Type1, Type2)
D1 Faraday Cup
Differential Cross Section of 3He(p,p+)4He
K.M. Furutani et al.,
PRC 50, 1561(1994).




3He(p,p+)4He
peak at 400 and 300 MeV.
The backgrounds were subtracted by fiiting.
Comparison with previous results.
Our results are consistent with them.
Absolute 3He Polarization
Results
 Ep = 400 MeV
Cell : Type1
PHe = (6.33±0.19)×104×VNMR
PHe = (2.51±0.09)×103×VNMR[He]
 Ep = 300 MeV
Cell : Type2
PHe = (5.42±0.32)×104×VNMR
PHe = (2.46±0.15)×103×VNMR[He]
Relation between Amp. and Pol.
Relation to AFP-NMR Amp.
PHe  2.50  0.0810  VNMR /[ He ]
3
p+3He Elastic Backward Scattering (EBS)



We measured the differential cross section and spin correlation
parameter Cyy of p+3He EBS at 400, 300, 200 MeV.
ds/dW are consistent with previous results.
Cyy are measured for the first time.
Calculated by A.P. Kobushkin
Summary
• Polarized 3He Target at RCNP



We have succeeded to stabilize the temperature within 0.1 oC by
using PID feedback system.
We measured the precise 3He density.
3He polarization was calibrated by 3He(p,p+)4He reaction.
Maximum : 19 %
Average : 12 %
3He polarization was smaller than other institutions.
• Problems


Rb polarization is small. (Laser power is not enough.)
Relaxation time is short because of magnetic field inhomogeneity at
experimental hall (1/ : 15 hours  4 hours).