The intensity distribution of X-ray<i>Pendellösung</i>fringes

The intensity distribution of X-ray diffraction topographs in Laue cases was measured for Si perfect crystals by microdensitometry with an accuracy of 1% at the maximum intensity. Both section and traverse topographs taken with {220} and {440} reflexions were studied, but the section topographs were the main interest. A least-squares analysis shows that the observed intensities can be represented well by the sum of two terms: the dynamical term based on the spherical wave theory and the kinematical term which has a form of attenuation because of the normal absorption. The latter term, however, is very small and its ratio to the former, evaluated at zero depth, was about 10-3 in the perfect crystals available.