Alignment of double-crystal diffractometers

A rapid method is described for aligning a double-crystal diffractometer based on the design of Hart (Characterization of Crystal Growth Defects by X-ray Methods, edited by Tanner & Bowen, pp. 483-485. Plenum Press, London, 1980). The theoretical intensity profiles are derived for variations in crystal tilt and rotation, and a method is described that uses these profiles to align any double-crystal diffractometer in a systematic way, suitable for computer automation. The alignment requirements for simple mismatch measurements are also given.