The analysis of liquid structure data from time-of-flight neutron diffractometry

Abstract

The authors discuss in detail the analysis of structural data on liquids obtained using time-of-flight neutron diffractometry, in particular the Liquids and Amorphous Materials Diffractometer (LAD) situated at the ISIS pulsed neutron source at the Rutherford Appleton Laboratory. A series expansion for the inelasticity corrections has been calculated to higher order than has been done before and it is shown that the new terms are significant. It is argued, however, that there are fundamental reasons why any such correction will be inadequate for the lowest-energy neutrons. The problem of combining the results from detectors at different angles is considered and the authors present a generally applicable method for doing this in such a way that the effect of instrumental resolution is readily included. These procedures are demonstrated and tested on data obtained in an experiment to measure the structure factor of molten CsCl at 670 degrees C, close to the melting point, and at 970 degrees C using LAD. The result at the lower temperature is in good agreement with a previous result obtained using the D4 steady state diffractometer at the High Flux Reactor of the Institut Laue-Langevin, Grenoble. The change in the structure factor between the two temperatures can be accounted for entirely in terms of density scaling indicating that there is little, if any, change in the pair correlation function g(r) as the temperature is raised.