Method for deducing anisotropic spin-exchange rates

Using measured spin-transfer rates from alkali-metal atoms to He-3, combined with spin-relaxation rates of the alkali-metal atoms due to He-3 and He-4, it should be possible to differentiate between isotropic and anisotropic spin exchange. This would give a fundamental limit on the He-3 polarization attainable in spin-exchange optical pumping. For K-He, we find the limit to be 0.90 +/- 0.11.