Determination of apertures in the focusing plane of X-ray powder diffractometers

Abstract

The basis for calculating divergence, receiving and anti-scatter slit widths is described. Expressions derived from ray diagrams and geometrical optics have been verified experimentally. Peak and integrated intensities are proportional to the divergence slit width WDS and are proportional to the angular aperture αp calculated assuming a point rather than a finite source. The intensity distribution at the specimen is determined by the fraction of the X-ray focal line source F that can be seen. In the practical case, where WDS is significantly greater than the projected source width WF, the intensity distribution on the specimen is uniform in the central region and has small shadowed regions on each side. The cases of a point source and WDS < WF are also described. Higher angles of view of the target provide higher and more uniform intensity distributions. Charts are included showing the length of specimen irradiated as a function 2θ for αp = 0.5° to 8°, and anti-scatter slit widths as a function of α for various receiving slit widths.