The experimental determination of the phases of X-ray reflections

The application of dynamical diffraction theory to the 'phase problem' for centric crystals shows that the intensities diffracted in simultaneous three-beam interactions display characteristic maxima and minima. The sequence in Which these appear on chart recordings is a sensitive function of the phase of the triplet involved in the interaction. The sequence is the same for all triplet phases of the same sign; it is reversed for those of the opposite sign. In earlier work a number of triplet phases in perfect crystals were determined. In the present work, several hundred triplet phases in mosaic crystals have been determined. Details of one of these investigations are reported in the following paper [Gong & Post (1983). Acta Cryst. A39, 719-724].