A compact polarization monitor for thermal beams of polarized hydrogen

Abstract The nuclear polarization of spin-polarized hydrogen gas targets can be measured using the spin coupling of electron and nucleus in the hydrogen atom. The polarized target atoms are excited by electron impact at low energy. Due to fine and hyperfine interaction the spin polarization of electron and proton is partially transferred to circular polarization of the emitted H α -light. In a weak magnetic field the light polarization is proportional to the initial nuclear polarization with a measured analyzing power of 0.33 ± 0.03. The simple principle allows a compact polarimeter setup. It can be used as target polarization monitor, e.g., for targets at low energy storage rings where weak guide fields at the target are required.