Formation of X-ray shift fringes and a new method for determination of the difference sign of interplanar distances

A detailed investigation of the conditions for the formation of X-ray shift fringes is carried out, aiming to apply these patterns to investigations of crystal imperfections. Expressions for the amplitudes and X-ray intensity distribution are obtained for a two-crystal interferometer, in which the interplanar distance between two reflecting planes, d, has a relative change(delta)d/d~=10^(-8)-10^(-5). It is theoretically proven and experimentally confirmed that the value of the period of interference bands essentially depends on the sign of (delta)d.