MEASUREMENT OF THE HE-4 CHEMICAL-POTENTIAL IN PHASE-SEPARATED HE-3-HE-4 LIQUID-MIXTURES

As a first step towards thermodynamic measurements in highly polarised dense He-3 fluids, an. accurate determination of the He-4 chemical po tential mu(4) was performed in, unpolarised phase-separated He-3-He-4 liquid mixtures at low pressures (0-1 bar) over a temperature range 0. 12-0.65 K. A method introduced by H. London and relying on heat flush effects was used. Two volumes containing : a) a cold, phase-separated helium mixture and b) a warmed, pure He-4 liquid are connected by a na rrow tube, and their temperatures are recorded under various condition s. The results agree with existing data obtained by the same technique for T > 0.2K, but cannot be analysed with the simple regular solution model fitting vapour pressure data. at T > 0.6K. The sensitivity of t he technique is shown, to be sufficient to observe expected effects of nuclear polarisation on mu(4).