Problems in the numerical calculation of the contrast of defects in X-ray traverse topographs

The simulation of section topographs of distorted crystals may be performed with good accuracy; it is now possible to use it as a tool to determine the quantitative parameters of various defects. The simulation of traverse topographs is a more complicated problem: it needs a tremendous amount of computation time, but the main difficulty arises from the numerical method itself. Reasons and a demonstration, with simulations of the contrast of a dislocation, are given why the only way to compute the traverse topograph is by the addition of the intensities due to an incident spherical wave. Nevertheless, the accuracy of the result remains poor.