Estimation of Single Crystal Integrated X-ray Intensity within a Designated (D?, D2?) Domain

Abstract

It is shown that measurement of the integrated intensity of a Bragg X-ray reflection within a precisely defined area of the (Aw, A2() distribution (Mathieson 1982a) is possible using a standard scintillation detector. The method involves an aperture system in front of the detector, consisting of two halves which are independently controlled so that both the width and position of the aperture are variable and can follow the A2() boundaries of the sections of any specified convex domain in (Aw, A2() space, as the specimen crystal steps in Aw. By taking account of the dispersion of the wavelength, crystal mosaicity and source components, the method can (a) exclude those extraneous contributions which, particularly at low () angles, constitute a major error source with conventional fixed-aperture procedures and (b) obviate the so-called truncation error at high () angles. This boundary-following method therefore provides, by a simple instrumental operation, a much closer estimate of the true integrated intensity of a Bragg reflection from a small single crystal than is feasible with the use of a fixed aperture. Once the main parameters of the experiment are determined, the procedure requires no greater expenditure of time than the traditional fixed-aperture method.