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 profile I ( y ) and its parameters, the shift of the centre of gravity 〈 y 〉 and the profile variation W . These are calculated in terms of exact expressions and approximate results. The obtained closed formulae for 〈 y 〉 and W augment analogous calculations for other aberrations, tabulated by Parrish and Wilson in the International Tables for X-ray Crystallography (Vol. III, 1995). Calculation of the peak profiles is verified by experiment.