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 He-3 target. The new method makes use of special properties of the reaction He-3(d,p)He-4. We demonstrate that for protons produced by this reaction at theta = 0 degrees, the polarization observables T-20 and C-z,C-z are related according to root 2T(20) + 3C(z,z) = -2. Using this result, we have made an absolute measurement of the target polarization in the Wisconsin double-cell polarized He-3 target. The calibration was carried out by observing the He-3(d,p)He-4 reaction with vector- and tenser-polarized deuterons of known polarization. The analyzing power T-20(0 degrees) at energy E-d = 2.1 MeV was first measured with the result T-20(0 degrees) = -0.530 +/- 0.012. The corresponding spin correlation coefficient is C-z,C-z(0 degrees) = -0.417 +/- 0.006. The target polarization, P-1, was then determined by measuring the 0 degrees 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. (C) 1999 Elsevier Science B.V. All rights reserved.