A method for checking X-ray diffractometer stability and its application

A statistical model of step-scanning of Bragg reflections on an X-ray diffractometer has been suggested. A method and software for stability checking of X-ray automatic diffractometers at the user's laboratory have been developed on the basis of this model. The method is an extension of the technique proposed by Dietrich (1976) and reveals the operational instability of the instrument by processing the data of repeated measurements of a reflection intensity profile of a test crystal. The developed software package gives information about the error in initial positioning, the speed instability of the goniometer and the instability of the X-ray source and detector. The method was applied to a number of automatic four-circle X-ray CAD-4 (Enraf-Nonius, Holland) and Syntex (USA) diffractometers. The results obtained indicate that the method has high sensitivity and can be useful for practical crystallographers to reveal defects of their instruments. (orig.)