Multiple-Beam Borrmann Effect in Perfect Crystals of Germanium and Silicon

The way of solving the dispersion equation system is outlined for the general three-beam case of X-ray diffraction. The numerical results obtained for the absorption coefficients mu((3)) in the (1 (1) over bar1) (20 (2) over bar) case in Ge and Si are consistent with the experimental data though reveal the familiar trend, mu((3))(calculated) <mu((3))(measured). A comparison is made between the theoretical results and the experimental data for the three- and four-fold Borrman effect in Ge; the discrepancies are interpreted in terms of the extremely high sensitivity of multiple-beam stationary wave-field absorption to internal strain fields of inherent defects.