Wavelength Calibration of Flat-Crystal and Convex Curved-Crystal X-Ray Spectrographs

Fixed-crystal spectrographs must be calibrated in terms of wavelength vs position on the film or detector array. This can be done either from the measured positions of lines with known wavelengths or from the geometrical design of the instrument. It is more accurate, however, to combine both kinds of information in a least-squares fitting method. This paper presents techniques for several spectrograph geometries, including flat and convex-curved crystals in reflection mode, with both flat and cylindrical film. Also treated is a less common case where the diffracting planes are inclined to the crystal surface. Uses of the calibration equations in wavelength determinations, resolution studies, and intensity measurements are discussed.