Measurements of ³He spin-exchange rates

Spin-exchange rate coefficients for Rb-³He are measured using three different methods. Two methods, using Rb repolarization and rate balance, require no assumption about the nature of the ³He wall relaxation and agree well; we find spin-exchange rate coefficients of 6.7×10^-20cm³/s and 6.8×10^-20cm³/s. These results agree with a recent repolarization measurement of Baranga and co-workers [Phys. Rev. Lett. 80, 2801 (1998)]. The third method uses the temperature dependence of the ³He relaxation and is 30% larger than the other two, implying a temperature-dependent wall or an unreasonably large value of the anisotropic spin-exchange interaction for Rb-³He. In the course of these measurements we developed and tested a new method for Rb density measurements under high power pumping conditions, and a new variant of Rb EPR polarimetry, both of which are described here.