Polarized, high-density, gaseousHe3targets

The technique of spin exchange between laser optically pumped alkali-metal vapor and ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ can provide several atm ${\mathrm{cm}}^{\mathrm{-}3}$ (≊${10}^{21}$ atoms in a volume of 6 ${\mathrm{cm}}^3$) of nearly 100% polarized ${}_{}{}^3{}_{}{}^{}\mathrm{He}$. We have recently produced 40% polarization of ${10}^{20}$ atoms of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ (3 atm in 1.3 ${\mathrm{cm}}^3$). It should therefore be possible to produce useful polarized ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ targets by this technique. The realization of a practical target is limited by the contribution to depolarization by ionization during bombardment. This has been studied with a 360-nA, 18-MeV α-particle beam with encouraging results. A ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ target with 50–90 % polarization and a thickness of ${10}^{20}$ atoms ${\mathrm{cm}}^{\mathrm{-}2}$ is feasible. This paper presents the principles of the technique, the recent progress on spin exchange with optically pumped alkali-metal vapor, and studies of ionization-induced depolarization.