International
Tables for Crystallography Volume C Mathematical, physical and chemical tables Edited by E. Prince © International Union of Crystallography 2006 |
International Tables for Crystallography (2006). Vol. C, ch. 7.4, p. 653
Section 7.4.1. Absorption^{a}Department of Physics, University of Ioannina, PO Box 1186, Gr-45110 Ioannina, Greece,^{b}Department of Physics, University of Warwick, Coventry CV4 7AL, England,^{c}Department of Physics, PO Box 9, University of Helsinki, FIN-00014 Helsinki, Finland, and ^{d}Chemical Crystallography Laboratory, University of Oxford, 9 Parks Road, Oxford OX1 3PD, England |
The positions and intensities of X-ray diffraction maxima are affected by absorption, the magnitude of the effect depending on the size and shape of the specimen. Positional effects are treated as they are encountered in the chapters on experimental techniques.
In structure determination, the effect of absorption on intensity may sometimes be negligible, if the crystal is small enough and the radiation penetrating enough. In general, however, this is not the case, and corrections must be applied. They are simplest if the crystal is of a regular geometric shape, produced either through natural growth or through grinding or cutting. Expressions for reflection from and transmission through a flat plate are given in Table 6.3.3.1 , for reflection from cylinders in Table 6.3.3.2 , and for reflection from spheres in Table 6.3.3.3 . The calculation for a crystal bounded by arbitrary plane faces is treated in Subsection 6.3.3.3 .
The values of mass absorption (attenuation) coefficients required for the calculation of corrections are given as a function of the element and of the radiation in Table 4.2.4.3 .