Mean kinetic energy of helium atoms in fluid3He and 3He–4He mixtures

Abstract

Momentum distributions and mean kinetic energies of helium atoms, in pure fluid3He and3He–4He mixtures,at T = 2 K and3He concentrationsof x = 0.20 and x = 1.00, are presented. The experimental technique employed is deep inelastic neutronscattering measurements in the eV energy range, with wavevector transfer of typically100 Å−1<q<250 Å−1. Single-particledynamical properties of 3He–4He mixtures are discussed in the context of previous results on mixtures at different concentrations and pure3He and4He. In the pure fluids,the kinetic energy of 3He and 4He are remarkably similar for molar volumes above25 cm3 mol−1, whilefor smaller molar volumes, upon approaching the liquid–solid transition, the kinetic energy is largerin 3He than 4He. On the other hand, the short-time dynamics of the heliummixture reveal quite a different picture with respect to the pure3He and 4He: the momentum distribution and mean kinetic energy of the light helium component areindependent of the molar volume and concentration.