ABSTRACT
With a conventional powder diffractometer, practical data collection rates can be obtained from laboratory X-ray sources with the utilization of a divergent beam illuminating a flat powder specimen. Sample preparation is relatively simple and can be applied to a variety of materials. However, the para-focusing optics of these diffractometers embody aberrations from the ideal focusing geometry, rendering the performance characteristics, reflected by profile displacement, profile breadth, profile asymmetry, diffracted intensity as a function of 28 angle, etc., to be a convolution of a number of contributing factors. To fully utilize the data from such equipment, the performance characteristics inherent to the diffractometer must be taken into account in the data analysis procedure. While the performance of such machines can be modeled, the more typical approach involves the use of standards for an analysis of instrument performance. The difficulties are compounded if the machines are set up incorrectly, as this results in additional aberrations, which are further convolved with those inherent to the para-focusing diffractometer. This results in a deterioration of the performance characteristics, which, while it may go undetected, affects the quality of the interpretation nonetheless. With the proper use of National Institute of Standards and Technology (NIST) standard reference materials (SRMs) the performance of equipment can be characterized accurately, allowing for the sources of error to be isolated and corrected.
