Measurements of the collective excitations of liquid helium have led to a detailed understanding of the microscopic dynamics in both the normal and superfluid (sf) phases. Inelastic neutron scattering has proven to be one of the most useful tools in studying these excitations. It is proposed to extend these studies to negative pressures. At low negative pressure the liquid is metastable, allowing measurements to be carried out. At larger negative pressures (around 9 bars), the speed of sound approaches zero and the liquid is no longer stable. Macroscopic samples (one or more cc. in volume) of liquid He at negative pressure will be created using a novel expansion cell. The time structure of a typical short-pulse neutron source will be used to carry out inelastic n scattering measurements in the interval between pressure equilibration and the nucleation of gas bubbles.
