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 Pqq of the 668 nm emission light from the optical pumping cell. From the measured target polarization we obtain a calibration constant K = Pt/Pqq = 11.57 ± 0.43. This result is in good agreement with the calibrations based on other techniques.