Small angle intensities from double reflections in powder samples

Abstract

A small angle intensity is to be expected from double reflections in any powder sample comprising small grains with random orientation. The inter-grain contribution is due to an hlcl reflection in one grain, followed by the same hkl reflection in another grain. The intra-grain contribution arises from a hlcl reflection followed by a h-kl reflection in the same grain. The inter-grain intensity is independent of grain size and falls off inversely as the scattering angle. The intra-grain intensity depends upon grain size, and fails off rapidly with scattering angle. Equations are obtained for both types of contribution. Cold work in a sample breaks up the original grains into small sub-grains with a small variation in orientation. The enhanced inter-grain contribution from these groups of sub-grains can produce a strong small angle scattering.