Polarized, high-density, gaseous He3 targets

The technique of spin exchange between laser optically pumped alkali-metal vapor and He3 can provide several atm cm-3 (Š1021 atoms in a volume of 6 cm3) of nearly 100% polarized He3. We have recently produced 40% polarization of 1020 atoms of He3 (3 atm in 1.3 cm3). It should therefore be possible to produce useful polarized He3 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 ±-particle beam with encouraging results. A He3 target with 5090 % polarization and a thickness of 1020 atoms cm-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.