Fine Structure of X-Ray Interferograms. I. A Two-Crystal System with a Non-Diffracting Zone (a Narrow Gap)

X-ray interferometrical patterns obtained by diffraction of an X-ray beam in a crystal system, consisting of a two-crystal system having a narrow gap and a thick absorbing crystal, is studied. The spacing of interbranch scattering fringes is theoretically calculated. It is shown that the presence of the thick crystal brings to a five- to tenfold enlargement of fringe spacing. For the first time fringes of interbranch scattering and moiré fringes are obtained on the same topograph.