The process of ${\mathrm{He}}^3$ nuclear polarization by metastability exchange with optically pumped metastable ${\mathrm{He}}^3$ atoms is described and experimental details given. Phenomenological theories are presented which explain the optical signals and the time variation of the polarization. The polarization is measured both optically and by nuclear magnetic resonance. Relaxation of the nuclear spins by diffusion through magnetic field gradients is discussed. When gradients are small, nuclear relaxation times as long as 4000 sec have been measured. The maximum polarization achieved was 40±5% in ${\mathrm{He}}^3$ gas at a pressure of one mm Hg.

• Received 5 August 1963

DOI:https://doi.org/10.1103/PhysRev.132.2561