Precise Proton-Polarization Standards Determined with a Lamb-Shift Ion Source Incorporating a Nuclear Spin Filter

The polarization of an 8-12-MeV proton beam produced by a Lamb-shift ion source has been determined with 0.4% absolute accuracy by an atomic-beam technique. The procedure, which involves selection of a single hyperfine state of fast $\mathrm{H}\mathrm{}\left(2s\right)\mathrm{}$ atoms, is ideally suited to routine monitoring of beam polarization. Absolute $p-{}_{}{}^4{}_{}{}^{}\mathrm{He}$ elastic-scattering analyzing powers measured with the calibrated beam are reported, and existing double-scattering data are compared with these results.