Single-particle mean kinetic energy in low-density supercritical
Consiglio Nazionale delle Ricerche (CNR) - Roma, Italy
2 Istituto Nazionale per la Fisica della Materia (INFM), UdR “Tor Vergata” Via della Ricerca Scientifica 1, 00133 Roma, Italy
3 Dipartimento di Fisica, Università degli Studi di Roma “Tor Vergata” Via della Ricerca Scientifica 1, 00133 Roma, Italy
Accepted: 31 January 2000
We report novel results from inelastic neutron scattering measurements at very high momentum transfer, 122 Å performed in supercritical 4He, along two very low-density isochores ( nm-3 and nm-3) in the temperature range 5–30 K. The experimental data have been analysed within the framework of the plane-wave Impulse Approximation and the temperature dependence of the single-particle mean kinetic energy has been derived. It is found that this quantity deviates from the classical behaviour in the whole temperature range explored, showing the quantum nature of this system even for these very low-density isochores, the lowest ever experimentally explored. For the higher density, the temperature evolution of the single-particle mean kinetic energy has also been derived using a path-integral Monte Carlo code. These quantum simulation results, as well as those already available for the low-density isochore, are in good agreement with the experimental data. It is pointed out that, at these densities, the temperature dependence of the mean kinetic energy is consistent with an anharmonic behaviour of 4He induced by the hard-core component of the interatomic potential.
PACS: 67.20.+k – Quantum effects on the structure and dynamics of nondegenerate fluids (e.g., normal phase liquid ) / 61.12.Ex – Neutron scattering techniques (including small-angle scattering)
© EDP Sciences, 2000