COLLECTIVE DYNAMICS IN LIQUID CESIUM NEAR THE MELTING-POINT

The coherent dynamic structure factor S(Q,omega) of liquid Cs has been measured by inelastic neutron scattering near the melting point at 308 K. Using triple-axis spectrometers at the Institut Laue-Langevin in Grenoble and at the Forschungs-Reaktor Munchen the scattering law was determined for energy transfers h-omega-BAR from -2 to 10 meV and for momentum transfers hQBAR between 0.2 and 2.55 angstrom-1. The measurement has been corrected for all significant effects, including multiple and incoherent scattering as well as resolution broadening. In this paper we present mainly experimental results including a table of the measured scattering law. The analysis of the dispersion relation and the full width at half maximum of the longitudinal current correlation function J1(Q,omega) reveals an anomalous dispersion due to shear relaxation in the liquid. In the vicinity of the structure-factor maximum the measured half-width of the coherent central peak of S(Q,omega) confirms recent theoretical assumptions of a collective-diffusion-like structural relaxation process in dense liquids near the melting point.