Three-beam X-ray diffraction – profile analysis

An original functional description of the intensity perturbation of the two-beam diffracted power caused by an interfering three-beam interaction has been developed. By using this approach in the analysis of measured three-beam profiles of α-oxalic acid dihydrate, parameters related to the Darwin mosaic model are refined. The final results indicate an anisotropy in both the mean domain size, measured along the secondary beam, and the block orientation, measured as the angular spread in the location of the three-beam point. The presented method relies on a procedure for merging the contributions to the perturbation originating from dynamical (coherent) and kinematical (incoherent) scattering processes.