Resolution Effects in the Measurement of Phonons in Sodium Metal

Abstract

In the course of making a detailed study of the phonons in Na metal using a triple‐axis neutron spectrometer we have observed anomalous, asymmetric, and, in some cases, extraordinarily broad or split resonances. In this paper we account for these effects quantitatively by performing a complete resolution analysis. This analysis includes fully the combined effects of vertical resolution, a highly anisotropic dispersion surface, the variation of the polarization vectors and the temperature factor inside the resolution volume, and the sample mosaic spread. The application of this calculation to the measurement of phonons in other materials is straightforward.