Separation of thermal diffuse scattering by NSE in diffraction studies

Abstract

Thermal diffuse scattering (TDS) is inelastic scattering arising mainly from acoustic phonons and which contaminates the purely elastic Bragg or purely elastic diffuse scattering when intensities are measured by standard diffraction methods. Corrections for the effect of TDS are classically done by more or less approximate calculations. These corrections are in general rather difficult because they suppose a knowledge of the dynamics of the system and of the resolution function of the diffractometer used. At higher temperatures and/or for soft materials these corrections may not be feasible at all. Experimental filtering of TDS is in principle possible by the neutron triple-axis technique and has actually been performed in certain special cases. But in general sufficient energy resolution to guarantee safe filtering can only be achieved by drastic beam collimations rendering the method im practicable intensity wise. Neutron spin echo (NSE) added to a triple-axis neutron diffractometer is shown here to be capable of providing improved resolution preserving good intensities such as to allow an efficient separation of purely elastic and low energy inelastic scattering.