Neutron and PIMC Determination of the Longitudinal Momentum Distribution of HCP, BCC and Normal Liquid 4 Het

Abstract

Abstract Deep inelastic neutron scattering has been used to measure the neutron Compton profile (NCP) of a series of condensed 4He samples at densities from 28.8 atoms/nm3 (essentially the minimum possible density in the solid phase) up to 39.8 atoms/nm3 using a chopper spectrometer at the Argonne National Laboratory Intense Pulsed Neutron Source. At the lowest density, the NCP was measured along an isochore through the hep, bcc, and normal liquid phases. Average atomic kinetic energies are extracted from each of the data sets and are compared to both published and new path integral Monte-Carlo (PIMC) calculations as well as other theoretical predictions. In this preliminary analysis of the data, account is taken of the effects of instrumental resolution, multiple scattering, and final-state interactions. Both our measurements and the PIMC theory show that there are only small differences in the kinetic energy and longitudinal momentum distribution of isochoric helium samples, regardless of their phase or crystal structure.