Number Density and Phase Diagram of DiluteHe3-He4Mixtures at Low Temperatures

Abstract

The molar volume at the saturated vapor pressure has been determined by a dielectric method for solutions containing up to 15 atomic percent of ${\mathrm{He}}^3$ in ${\mathrm{He}}^4$ between 0.025 and 1.2°K. In the single-phase region there is a pronounced thermal expansion from which it is deduced that the derivative of the ${\mathrm{He}}^3$ effective mass with respect to pressure is for low concentrations [$(0.0151\mathrm{}\pm 0.0006)m^{*}$] ${\mathrm{atm}}^{-1\mathrm{}}$. The single-phase measurements also show that at 0°K and for low concentrations, ${\mathrm{He}}^3$ atoms occupy (1.284 ± 0.005) times the volume occupied by ${\mathrm{He}}^4$. In the two-phase region, the concentration of the lower phase at 0°K is found to be (6.40 ± 0.07)% ${\mathrm{He}}^3$. The ${\mathrm{He}}^3$ chemical potential along the solubility curve has been obtained and compared with the predictions of Bardeen, Baym, and Pines (BBP). Assuming the effective interaction originally proposed by BBP, the binding energy at 0°K of a single ${\mathrm{He}}^3$ atom in ${\mathrm{He}}^4$ is found to be ${L_3}^0+R(0.284\mathrm{}\pm 0.010)°$K, where ${L_3}^0$ is the latent heat of pure ${\mathrm{He}}^3$ at 0°K.