FINAL-STATE EFFECTS AND MOMENTUM DISTRIBUTION IN NORMAL LIQUID-HE-4

We have performed time-of-flight neutron scattering experiments, measu ring the dynamic structure factor S(Q, omega) of liquid He-4 with high resolution and very good statistical precision. A continuous range of wavevectors Q from 3 to 17 angstrom-1 was covered at T = 2.5 K, while at T = 1.42 K the Q-range from 2 to 10 angstrom-1 was covered. As par t of a lengthy and careful data reduction procedure, the TOF data were rebinned onto constant-Q representations for use in the subsequent da ta analysis. Taking instrumental resolution into account, clear oscill ations in both the width and position of the recoil peak are observed at both the measured temperatures up to a wavevector in excess of 12 a ngstrom-1, which are caused by coherence effects. The measured S(Q, om ega) is analysed using a recent expression by Glyde, which expresses t he intermediate dynamic structure factor in powers of time. Very good agreement is obtained by fitting the normal fluid data to his expressi on with three free parameters related to the final-state effects and t he central moments of the momentum distribution. The momentum distribu tion in the normal fluid state is found to be significantly non-Gaussi an and agrees well with PIMC calculations of the momentum distribution . The extracted value for the mean kinetic energy per atom [K] is in g ood agreement with previous neutron and X-ray scattering measurements.