Observation of the Stages of Homogeneous Nucleation in Isotopic Solid Helium Mixtures

We report a study of nucleation and phase separation in solid helium isotopic mixtures using a combination of pressure and NMR measurements. The experiments were performed both at pressures where the phase-separated ³He inclusions formed as solid droplets and as liquid droplets. Our observations clearly indicate the three stages of the nucleation process: creation of nucleation sites; growth of the new-phase component at these nucleation sites; and finally dissolution of sub-critical droplets with consequent further growth of super-critical droplets or ‘Ostwald ripening’.