PHASE-SEPARATION KINETICS OF SOLID HE-3-HE-4 MIXTURES

The kinetics of isotopic phase separation in solid mixture of He-3 in He-4 with the initial concentration 2.05 % at various molar volumes ha s been investigated by precise pressure measurements. It has been show n that during both stepped and fast cooldown into the metastable regio n the equilibrium of coexisting phases is described by the exponential law with a characteristic time constant tau. The value of tau is foun d to decrease as the molar volume increases and the temperature lowers . It confirms that the growth of the He-3-rich phase is connected with nonthermally activated (quantum) diffusion in the gas of delocalized He-3 quasiparticles. The obtained experimental results can be describe d only qualitatively by current kinetic theory of binary quantum solid mixtures. The conditions permitting the realization of the isotopic p hase separation during the time observed in the experiment are analyze d. The effective quantum diffusion coefficient providing required He-3 atoms transport is about an order of magnitude higher than the corres ponding value measured in NMR experiments. These conditions are probab ly fulfilled at the big concentration gradient which takes place at is otopic phase separation. The corresponding kinetic theory should be de veloped.