The breadth and shape of instrumental line profiles for the powder diffraction station 2.3 at the Daresbury Laboratory SRS

The instrument resoln. function (IRF) was measured for a std. KCl powder sample. Besides the high flux and beam monochromaticity the main feature concerns line profile width and shape. Narrow peaks (FHWM 0.04-0.08° 2θ) were obsd. over a wide angular range, whereas line widths increase significantly at higher angles for conventional diffractometers. This characteristic of the 2.3 instrument is due to the long slit assembly in the path of the diffracted beam, which limits the peak width and at the same time increases the recorded intensity. Any nonparallelism of the foils leads to measurable extraneous scattering and a corresponding modification of the line-profile tails. This effect is modeled by 2 satellite peaks, 0.1-0.2° on each side of the Bragg peak. The widths are 0.2° and the intensity is a few percent of the main peak. These parameters are const. over a range of 2θ considered. As with the main peak, the satellites can be quantified to correct data used for line profile anal. or in other applications. [on SciFinder(R)]