Specific features of two diffraction schemes for a widely divergent X-ray beam

We investigated the specific features of two diffraction schemes for a widely divergent X-ray beam that use a circular diaphragm 30-50 mu m in diameter as a point source of characteristic radiation. In one of the schemes, the diaphragm was set in front of the crystal (the diaphragm-crystal (d-c) scheme); in the other, it was installed behind the crystal (the crystal-diaphragm (c-d) scheme). It was established that the diffraction image in the c-d scheme is a topographic map of the investigated crystal area. In the d-c scheme at L = 2l (l and L are the distances between the crystal and the diaphragm and between the photographic plate and the diaphragm, respectively), the branches of hyperbolas formed in this family of planes (hkl) by the characteristic K (alpha) and K (beta) radiations, including higher order reflections, converge into one straight line. It is experimentally demonstrated that this convergence is very sensitive to structural inhomogeneities in the crystal under study.