Absorption Factor in Crystal Spectroscopy

Abstract

In the determination of the structure of a crystal with x-rays, it is essential that a reliable set of diffraction intensity data be obtained. During its passage through the crystal, the x-ray beam suffers a diminution in intensity due to absorption by the crystal itself, and the extent of this absorption will in general be different for different crystal planes. This variable factor has long been troublesome in crystal work, since its estimation presents a difficult problem even in simple special cases. The case of a cylindrical powder sample has been treated by various investigators, notably A. Claassen and A. J. Bradley. The latter also treats the case of equatorial reflections from a single crystal ground to a cylinder. O. P. Hendershot has recently published a method applicable to a crystal of any shape but restricted to crystals of high absorbing power. Absorption effects in Weissenberg photographs have been treated by A. F. Wells and M. J. Buerger. In all these methods the computational labor is great, and the general case has not, to the author's knowledge, been treated. In view of these difficulties the usual procedure is to use a crystal so small as to make absorption negligible (necessitating long exposure) or to hold this unknown factor responsible for poor intensity agreement. A graphical method for treating absorption in a crystal of any size, shape and absorbing power, which has proved useful in the author's work, is here presented.