Silicon-crystal rocking curves are measured with a high angular resolution (~0.1") under conditions of the Borrmann effect resonant suppression by transverse ultrasonic vibrations. It is shown that on the curves deep minima appear whose positions depend on the vibrational frequency, in agreement with the theory.

No abstract

An experimental investigation of Borrmann effect resonance suppression by transverse ultrasonic vibrations with wavelengths, approximating the extinction length is carried out. A theory of this phenomenon is developed. It is shown that X-ray acoustic resonance allows to measure the X-ray atomic scattering factor with a relative accuracy of iz IY-,, as well as to investigate the shape of the dispersion surface of X-ray dynamical diffraction.IIposeneHo a~c n e p n~e~~a n b~o e nccnenoBame p e 3 o~a~c~o r o nonaBneHm a @ @ e~~a BOpMaHa IIOIIepe ¶HbIMU YJIbTpa3BYKOBbIMU KOne6aHHHMH C DJIEIHaMH BOJIH, 6JIU3HUMU H AJIUHe 3KCTUHKqHU. Pa3BHTa TeOpHR BTOrO IIBJIeHHII. n O K a 3 a H 0 , ¶TO peHTreEOaKyCTUW3CHIlfi pe3OHsuIC IIO3BOJIHeT E3MepHTb aT0-m @aKTOp PaCCeHIWU peIiTlY!HOBCK€iXnticnepcuomiofi nosepxHocTH nmaMurIecKofi na@paKqmi pemreHoBcmx nysefi.

The spatial intensity profile of an X-ray beam reflected by a crystal with microdefects in the Bragg case is considered. A practically pure diffuse component was measured at the tail of the intensity distribution. From these data, static Debye-Waller factors of nearly perfect silicon crystals were obtained.

Bragg and diffuse scattering contributions to a reflection can be separated using the intensity dependence on the amplitude of transverse ultrasound excited in the crystal. The method is based on the fact that a weak ultrasound with wavelength equal to the extinction length suppresses almost completely the anomalous transmission of the coherent (Bragg) beam in a sufficiently thick absorbing crystal and does not affect diffuse scattering. Both parameters characterizing diffraction in a slightly imperfect crystal, the static Debye-Waller factor and the coefficient of additional absorption due to diffuse scattering, have been determined for a silicon crystal containing oxide precipitates after heat treatment.