Collective excitations in liquid lead

Abstract

Neutron inelastic scattering experiments have been performed to measure the scattering function S(Q, nu ) for liquid lead at 623K in the range of wavevectors Q from 0.4 to 1.6 AA-1. For Q<or approximately=1.2 AA-1 peaks in S(Q, nu ) are observed for non-zero frequencies nu , and their positions are found to lie on a fairly well defined 'dispersion curve'. The maximum frequency ( approximately 1.8 THz) occurs at QO/2, where QO(=2.2 AA-1) is the value of Q at the first peak in the static structure factor S(Q). At small Q the 'dispersion curve' appears to have a slope consistent with the velocity of sound in liquid lead. No experimental evidence for transverse excitations in the liquid is found.