On the geometrical conditions for recording X-ray topographs of large crystal slices

Geometrical aspects of large-scale transmission X-ray topography with Kα₁ radiation have been considered. It is shown that the height of a crystal slice which can be effectively recorded is given as H_eff = 2L(Δλ/λ)^1/2, where L is the source-to-sample distance and Δλ is the wavelength difference for the Kα doublet. A geometrical scheme termed the moving-slit simulation has been developed to examine the influence of various experimental parameters such as the widths of source and slits, the involved distances and the adjustment of the sample. The usefulness of this scheme is demonstrated experimentally.