The shapes of single-crystal neutron reflections in relation to their experimental components

Abstract

The shapes of Bragg reflections in Δω, Δ2θ space, resulting from the diffraction of monochromated neutrons from a small single crystal, c, are related, by means of a graphical or diagram approach rather than the more usual analytical treatment, to the various components of the experimental arrangement, namely an extended-face monochromator crystal, M, its mosaic spread and the interaction of the wavelength dispersions of M and of c. The last component contributes significant variation in shape with change in θc, or, more generally, in t = (tan θc)/(tan θM). The present approach gives a clearer appreciation of the rôles of the various components than occurred in an earlier treatment [Mathieson (1985). Acta Cryst. A41, 309-316] and so has heuristic value as an aid in obtaining a proper understanding of the interaction between source/monochromator crystal/specimen crystal and also in estimating experimental parameters for modelling reflections and defining truncation limits. The graphical approach in Δω, Δ2θ space can assist in the investigation of special features of Bragg reflections.