Spin transport in dilute, spin-polarized solutions of helium-three in helium-four

We have investigated $\sp3$He spin diffusion in two dilute solutions of $\sp3$He in $\sp4$He, with atomic fraction $x\sp3=1.82\times 10\sp{-3}$ and 6.26 $\times$ 10$\sp{-4}$, spin-polarized by an 8 T field. We do not find evidence that the diffusion coefficient for spins transverse to the average magnetization ($D\sb\perp$) declines or saturates at temperatures down to 0.20$T\sb{\rm F}$, contrary to previous experiment (Gully and Mullin 1984) but in accord with current theory. We have compared our measurements with the latest theory of Jeon and Mullin (1991); our data is mostly in good agreement with their theory if a slightly modified version of a $\sp3$He-$\sp3$He interaction due to Ebner (1967) is used. The congruence between data and theory supports the conclusion that the s-wave approximation to the interaction is not useful for transport calculations even for these rather dilute solutions. There may be an one unresolved discrepancy: our diffusion constant for the lowest concentration at the lowest temperatures is 25% higher than theory predicts. This could be due to a polarization dependance for $D\sb\perp$ or to a modification of the boundary condition by a bound $\sp3$He state, or possibly due to errors in the theoretical calculation