Presentation on theme: "Development of a Polarized 3 He Target at RCNP Youhei Shimizu RCNP, Osaka University."— Presentation transcript:
Development of a Polarized 3 He 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. 3 He Target 1.2. Elastic Backward Scattering 2.Polarized 3 He Target at RCNP 2.1. Target apparatuses 2.2. Measurement of 3 He density 3.Measurement of 3 He Polarization 3.1. AFP-NMR Method 3.2. 3 He(p, + ) 4 He Reaction 3.3. Absolute 3 He Polarization 4.Summary
3 He Target The relative strength of target-related spin dependent effects is larger than for any other dense nuclei. The precise 3 He ground state wave function is obtained by Faddeev calculation. High density and the high degree of polarization. + + 3 He T =100MeV + + 13 C T =132MeV + + 15 N 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+ 3 He 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, 3 He, ) 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 3 He target at RCNP.
Polarized 3 He Target Meta-stability exchange method Spin-exchange method Easily application for high density target 1)2 3 S 1 meta-stable 3 He 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 3 He nucleus via the spin-exchange collision.
Spin-Exchange Method The Rb electron polarization is transferred to the 3 He 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 3 He 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 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. Type1Type2 : 20 hours V T : 227 cm 3 V P : 120 cm 3 : 15 hours V T : 224 cm 3 V P : 286 cm 3
The Measurement of 3 He Density In order to obtain the cross section and the absolute 3 He polarization, it is necessary to know the density of the 3 He in the cells and its error. The 3 He density of our cells was measured by using the broadening of the Rb resonance absorption lines by 3 He density in same manner as Romalis et al., PRA 56, 4569 (1997). Setup of an optical measurement Results Absorption width (GHz) Density (amgat) Type1 60.1±0.13.57±0.08 Type2 62.9±0.43.65±0.07 The absorption width and 3 He densities at thermal equilibrium.
3 He(p, + ) 4 He Measurement of the 3 He Polarization 3 He polarization was monitored by AFP-NMP method. NMR signal is proportional to the degree of polarization. The 3 He 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 C yy takes the constant value of 1. AFP (Adiabatic Fast Passage) - NMR
D1 Faraday Cup Experimental Setup Grand Raiden Measurement 3 He(p, + ) 4 He reaction at 0 degree Observables Differential Cross section d /d 3 He Polarization Polarized proton beam Energy: 400, 300 MeV Polarization: 70 % Intensity: 10 – 40 nA Polarized 3 He gas target Spin exchange type Polarization: 12 % in average Both cells (Type1, Type2)
Differential Cross Section of 3 He(p, + ) 4 He 3 He(p, + ) 4 He 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 3 He Polarization Relation between Amp. and Pol. Results E p = 400 MeV Cell : Type1 P He = (6.33±0.19)×10 4 ×V NMR P He = (2.51±0.09)×10 3 ×V NMR [He] E p = 300 MeV Cell : Type2 P He = (5.42±0.32)×10 4 ×V NMR P He = (2.46±0.15)×10 3 ×V NMR [He] Relation to AFP-NMR Amp.
p+ 3 He Elastic Backward Scattering (EBS) We measured the differential cross section and spin correlation parameter C yy of p+ 3 He EBS at 400, 300, 200 MeV. d /d are consistent with previous results. C yy are measured for the first time. Calculated by A.P. Kobushkin
Summary Polarized 3 He Target at RCNP We have succeeded to stabilize the temperature within 0.1 C by using PID feedback system. We measured the precise 3 He density. 3 He polarization was calibrated by 3 He(p, + ) 4 He reaction. Maximum : 19 % Average : 12 % 3 He 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).