Polarization measurement for polarized gas targets

Abstract

Recently proposed experiments with polarized gas targets in storage rings require methods to measure the target polarization to an accuracy of a few percent or better. The task is made more difficult because the target atoms are injected into a long, narrow target cell to increase the target thickness available from atomic beam sources or optically pumped sources. Here we propose to extract ions formed in the cell by the charged particle beam, and to measure their polarization by nuclear or atomic methods. The advantage of this method is that the average target polarization is determined independent of possible spatial variations of target polarization. The proposed method was applied to a deuterium gas target, whose tensor polarization was measured by means of the 3H(d, n) 4He reaction. We show that uniform ion extraction can be achieved for a cell with a length-to-diameter ratio of 30. We find that the deuterons in molecules formed by recombination of polarized deuterium atoms are almost completely depolarized. Thus target polarization measurements must include measurements on molecules as well as atoms. We discuss nuclear reactions suitable to measure the polarization of H and D targets, as well as atomic methods to measure the polarization of the extracted ions.