PHASE-SEPARATION CURVE OF HE-3-HE-4 MIXTURES UNDER PRESSURE

The solubility of He-3 in He-4 has been measured under pressure up to 20 bars in the temperature range between 1 and 250 mK. At temperatures below 60 mK, the solubility varies as T2 at all pressures. The coefficient of the T2 term at 0 bar, beta, is 8.29+/-0.03 K-2, lower than the values of 9-11 K-2 reported previously. The value of beta rapidly decreases down to 3.92+/-0.03 K-2 at 15 bars with increasing pressure. The interaction potential between He-3 quasiparticles is obtained by analyzing the solubility data on the basis of Ebner's formula. The effective mass derived from the potential has a weak and positive dependence on the He-3 concentration at all pressures.