Diffraction of x rays at a Bragg angle of pi/2 (back reflection) with consideration of multiwave effects

The energy dependence of the back reflectivity in the dynamical diffraction of x rays at a Bragg angle of pi/2 (back diffraction) in perfect crystals of cubic symmetry (silicon) is investigated theoretically. In this case str ict backscattering is realized only under the conditions of multiple diffra ction. The features of the influence of multiple diffraction on back reflec tion in the energy range near the nuclear resonance radiation energy of 14. 41 keV for Fe-57 nuclei, specifically in the six-wave case, including the s ilicon (1,9,9) reflection (with an energy of 14.57 keV), which can be inves tigated experimentally with high energy resolution (1 meV) using synchrotro n radiation and a monochromator developed for nuclear resonant absorption, are thoroughly studied. It is shown that the back reflectivity observed und er the conditions of multiple diffraction has several maxima on the plot of its energy dependence with a value at each maximum smaller than half, in c ontrast to two-wave diffraction, where there is one maximum with a value cl ose to unity. (C) 1999 American Institute of Physics. [S1063-7761(99)01309- 8].