Enhanced polarization and mechanisms in optically pumped hyperpolarized He3 in the presence of He4

This work reports an enhanced polarization and mechanisms in optically pumped (OP) hyperpolarized He3 in the presence of He4. The cells contain Rb metal, 60-torr N2, and different pressures of He3 and He4. In the absence of He4, the polarization of He3 increases monotonically from 4.5% to 8% when the pressure of He3 is increased from 300 to 1500 torr. In the presence of 1850-torr He4 gas, the polarization of He3 is enhanced from 7% to 30% for a cell containing 600-torr He3 and 60-torr N2. The wall relaxation factors X for OP cells with and without buffering He4 gas were derived. It was found that the He4 gas confines the He3 atoms to a diffusion-limited region which effectively reduces the wall relaxation factor X. Mechanisms contributed to relaxation are addressed and discussed.