Geometrical equatorial aberrations in a Bragg–Brentano powder diffractometer with a linear position-sensitive detector

Abstract

The use of a position-sensitive detector with a Bragg–Brentano diffractometer implies the registration of the diffracted beam at a finite distance from the true focusing point. This gives rise to an aberration which is characterized by the peak intensity profileI(y) and its parameters, the shift of the centre of gravity 〈y〉 and the profile variationW. These are calculated in terms of exact expressions and approximate results. The obtained closed formulae for 〈y〉 andWaugment analogous calculations for other aberrations, tabulated by Parrish and Wilson in theInternational Tables for X-ray Crystallography(Vol. III, 1995). Calculation of the peak profiles is verified by experiment.