Pressure dependence of the isotopic phase separation temperature in solid He 3 - He 4 mixtures

The isotopic phase separation temperature of solid mixtures of $^{4}\mathrm{He}$ in $^{3}\mathrm{He}$ has been measured as a function of pressure ($31 \mathrm{atm}\ensuremath{\lesssim}P\ensuremath{\lesssim}42 \mathrm{atm}$) for $^{3}\mathrm{He}$ mole fractions $x$ greater than 0.900. The phase separation temperature was found to increase with decreasing pressure, as predicted by Mullin. The results are compared with other experiments and with theoretical calculations.