Development of a Polarized 3He Target at RCNP

Youhei Shimizu

RCNP, Osaka University

CollaboratorsRCNP, Osaka University : Y. Shimizu, K. Hatanaka, Y. Sakemi, A. Tamii, H.P. Yoshida, M. Uchida, Y. Shimbara, K. Fujita, Y. Tameshige, H. MatsubaraCNS, University of Tokyo : T. Uesaka, T. Wakui, T. Kawabata, K. Suda, Y. SasamotoSaitama University : K. ItohKyushu University : K. Sagara, T. Wakasa, T. Kudoh, M. Tomiyama, H. OhiraOsaka University : T. AdachiTohoku University : H. OkamuraRIKEN : H. UenoBogoloyubov Institute for Theoretical Physics : A.P. Kobushkin

Contents1. 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,+)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.

• The precise 3He ground state wave function is obtained by Faddeev calculation.

• High density and the high degree of polarization.

+ + 3He T=100MeV + + 13C T=132MeV + + 15N T=164MeV

Elastic pion scattering

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).

p+3He Elastic Scattering

The cross section at back angles show a rising pattern which is energy dependent.

In order to reproduce the d/d 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.

Elastic Backward Scattering (EBS) Structure of the light nuclei (d, 3He, ) 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.

M.S. Abdelmonem and H.S. Sherif, PRC 36, 1900 (1987).

We developed a thick and highly polarized 3He target at RCNP.

Polarized 3He Target

• Meta-stability exchange method

• Spin-exchange method

Easily application for high density targetEasily application for high density target

1) 23S1 meta-stable 3He atoms are directly polarized by an optical pumping method ( = 1.084 m).

2) The polarization of the meta-stable state is transferred to the ground state via the meta-stability exchange reaction.

1) Rb vapor is polarized by optical pumping with a circularly polarized light ( = 794.7 nm).

2) The Rb electron polarization is transferred to the 3He nucleus via the spin-exchange collision.

Spin-Exchange Method

3He

Spin Exchange

HyperfineInteraction

SE

Spin Relaxation

Rb 3He

3He Polarization

3He Rb

e e

52S1/2

52P1/2

mi = 12 mi = 12

radiationlessquenching from N2

Spin Relaxation

OpticalPumping

SD

opt

collisional mixing Rb Polarization

The Rb electron polarization is transferred to the 3He nucleus via the spin-exchange collision.

Rb vapor is polarized by optical pumping with a circularly polarized light ( = 794.7 nm).

The Schematic view of the Polarized 3He Target

COHERENT FAP-79-30C-800LBDiode Laser

Power : 60 WWavelength : 795 nm

Temperature Dependence of the Wavelength The center of wavelength is dependent on temper

ature and current. It was necessary to lock onto the Rb D1 resonanc

e line. In order to adjust the wavelength to the Rb D1 res

onance line, the laser diode is cooled down to 22.3 C 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 C.

Target Cell The cell had a thin window of 100 m 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.

Pumping Cell

Target Cell

100 mm

50 m

m

Thin windowof 0.4 mm

30 m

m

70 mm

Pumping Cell

Target Cell

60 m

m

100 mm

70 mm

50 m

mThin windowof 0.1 mm

Type1 Type2

: 20 hoursVT : 227 cm3

VP : 120 cm3

: 15 hoursVT : 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

Absorption

width (GHz)Density (amg

at)

Type1 60.1±0.1 3.57±0.08

Type2 62.9±0.4 3.65±0.07

The absorption width and 3He densities at thermal equilibrium.

• 3He(p,+)4He

Measurement of the 3He Polarization

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

Time development of NMR signal

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.

• AFP (Adiabatic Fast Passage) - NMR

D1 Faraday CupD1 Faraday Cup

Experimental Setup

Grand RaidenGrand RaidenGrand RaidenGrand Raiden

• Measurement 3He(p,+)4He reaction at 0 degree

• Observables Differential Cross section d/d 3He Polarization

• Polarized proton beam Energy: 400, 300 MeV Polarization: 70 % Intensity: 10 – 40 nA

• Polarized 3He gas target Spin exchange type Polarization: 12 % in average Both cells (Type1, Type2)

Differential Cross Section of 3He(p,+)4He

3He(p,+)4He peak at 400 and 300 MeV. The backgrounds were subtracted by fiiting. Comparison with previous results. Our results are consistent with them.

K.M. Furutani et al.,PRC 50, 1561(1994).

Absolute 3He Polarization

Relation between Amp. and Pol.

Results

Ep = 400 MeV Cell : Type1 PHe = (6.33±0.19)×104×VNMR

PHe = (2.51±0.09)×103×VNMR[He]

Ep = 300 MeV Cell : Type2 PHe = (5.42±0.32)×104×VNMR

PHe = (2.46±0.15)×103×VNMR[He]

]He/[1008.050.2 NMR3

He VP ]He/[1008.050.2 NMR3

He VP

Relation to AFP-NMR Amp.

p+3He Elastic Backward Scattering (EBS) We measured the differential cross section and spin correlation parame

ter Cyy of p+3He EBS at 400, 300, 200 MeV.

d/d 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 C by using PID feedback system.

We measured the precise 3He density. 3He polarization was calibrated by 3He(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 a

t experimental hall (1/ : 15 hours 4 hours).