Neutron scattering studies of the dynamic structure of liquid 4He

Several aspects of the dynamic structure of liquid 4He have been studied by means of neutron inelastic scattering at selected temperatures, pressures, and values of the wave vector transfer Q. In particular, the Van Hove scattering function has been determined for certain conditions. It changes markedly with pressure. The results appear to be describable in terms of one-phonon and multiphonon scattering with no indication that it is necessary to invoke the existence of two-roton bound states. They do, however, indicate that there is a strong interference between one-phonon and multiphonon scattering processes which in turn indicates that liquid helium is very 'anharmonic'. (author)