Method for deducing anisotropic spin-exchange rates

Using measured spin-transfer rates from alkali-metal atoms to $^{3}\mathrm{He}$, combined with spin-relaxation rates of the alkali-metal atoms due to $^{3}\mathrm{He}$ and $^{4}\mathrm{He}$, it should be possible to differentiate between isotropic and anisotropic spin exchange. This would give a fundamental limit on the $^{3}\mathrm{He}$ polarization attainable in spin-exchange optical pumping. For K-He, we find the limit to be $0.90\ifmmode\pm\else\textpm\fi{}0.11$.