Collective Excitations in Liquid Helium at Negative Pressures

对液氦集体激发的测量， 从而详细了解了 正常和超流体（SF）相。 非弹性中子 散射已被证明是最有用的工具之一， 研究这些激励。 建议延长这些 研究负压。 在低负压下， 液体是亚稳态的，允许进行测量。 在较大的负压下（约9巴），声速 接近零，液体不再稳定。 宏观 样品（一个或多个CC.以体积计）的液体He在负 将使用新型膨胀单元产生压力。 的时间 将使用典型短脉冲中子源的结构来 进行非弹性n散射测量， 压力平衡和气泡成核之间的关系。

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.