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

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 T20 and Cz,z are related according to 2T20+3Cz,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 T20(0°) at energy Ed=2.1 MeV was first measured with the result T20(0°)=−0.530±0.012. The corresponding spin correlation coefficient is Cz,z(0°)=−0.417±0.006. The target polarization, Pt, 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=Pt/P⊙=11.57±0.43. This result is in good agreement with the calibrations based on other techniques.