Absolute calibration of a double-cell polarized 3He gas target

Abstract

We introduce a new method for determining the polarization of the atoms in a polarized 3He target. The new method makes use of special properties of the reaction 3He(d,p) 4He. We demonstrate that for protons produced by this reaction at θ=0°, the polarization observables T 20 and C z, z are related according to 2 T 20+3C z,z=−2 . Using this result, we have made an absolute measurement of the target polarization in the Wisconsin double-cell polarized 3He target. The calibration was carried out by observing the 3He(d,p) 4He reaction with vector- and tensor-polarized deuterons of known polarization. The analyzing power T 20(0°) at energy E d=2.1 MeV was first measured with the result T 20(0°)=−0.530±0.012. The corresponding spin correlation coefficient is C z, z (0°)=−0.417±0.006. The target polarization, P t, was then determined by measuring the 0° proton asymmetry with vector-polarized deuterons. During the measurement, the relative target polarization was monitored by measuring the circular polarization P ⊙ of the 668 nm emission light from the optical pumping cell. From the measured target polarization we obtain a calibration constant K= P t/ P ⊙=11.57±0.43. This result is in good agreement with the calibrations based on other techniques.