Elastic scattering and the associated anomalous dispersion in the vicinity of Cd, In, Sn and Sb, K-absorption edges

Using nearly monoenergetic unpolarized K alpha X-rays with energies E = 17.44-42.75 keV, differential elastic scattering cross sections for Cd, In, Sn and Sb were measured at an angle of 90 degrees to assess the contribution of anomalous dispersion in the vicinity of K-absorption edges. An X-ray tube with a secondary target arrangement was used to obtain the monoenergetic radiation. A new method is developed to estimate the degree of monochromaticity, geometrical effects of the measuring system, solid angle correction and some considerations which are necessary in experiments using an X-ray tube with secondary target arrangement. Experimental results are compared with theoretical elastic scattering cross sections calculated using relativistic form factors (RFFs), relativistic modified form factors (RMFs), a combination of RFFs, RMFs and angle-independent ''anomalous'' scattering factors (ASFs), and relativistic numerical calculations based on multipole expansion of the second order S-matrix approach. Fairly good correspondence is observed between the experimental results and a combination of RFFs with ASFs above and below the edges. The experimental results are in excellent agreement with S-matrix values and a combination of RMFs with ASFs above and below the edges of Cd, In, Sn and Sb. However, the differences are larger nearer to the edges indicating the importance of anomalous terms in reproducing ''anomalous'' behaviour of the K-threshold regions. (C) 1997 Elsevier Science Ltd.