Diffusion Coefficients and Nuclear Magnetic Susceptibility of DiluteHe3-He II Solutions

Measurements of the spin-diffusion coefficient and the nuclear magnetic susceptibility of ${\mathrm{He}}^3$-He II solutions of molar concentrations between 0.030 and 3.0% have been made at temperatures above 0.4°K. The diffusion measurements show that the reciprocal of the spin-diffusion coefficient varies linearly with ${\mathrm{He}}^3$ concentration. The constant term is identified as the reciprocal of the binary diffusion coefficient. Results for the binary diffusion coefficient are in agreement with the results of other measurements where comparison can be made. Between 0.8 and 1.6°K, the binary diffusion coefficient varies exponentially with the reciprocal of the temperature, in a manner consistent with the roton excitation energy of 8.65°K. The susceptibility exhibits only small deviations from perfect-Fermi-gas behavior. A calculation of the effect on the susceptibility of the direct interaction between ${\mathrm{He}}^3$ quasiparticles made by utilizing an effective potential indicates that deviations from perfect-Fermi-gas behavior are small. There is reasonably good agreement between the measured and the calculated temperature dependence of the susceptibility.