  The Time-of-Flight and Neutron-Spin-Echo techniques have been applied for the
research of ultrasonic effect at the cold neutron diffraction in mosaic single
crystals (KBr and mica). It was found that h.f. ultrasound intensifies
quasi-elastic neutron scattering and this effect cannot be explained as a
result of neutron scattering by thermal phonons in a sample heated by
ultrasound; neither can it be interpreted in the context of standard secondary
extinction theory. A new modified model is proposed based on the assumption
that the angular distribution function describing mosaic block disorientation
is not smooth but contains deep narrow troughs. This model is qualitatively
equivalent to the preposition about existence large block structure of sample.
The corresponding kinetic equations are formulated and exactly solved. The
results obtained correlate well with experimental data. Our results evidence
that such an approach is applicable for studying the ultrasonic effect at
neutron diffraction in different technologies dealing with mosaic single
crystals. PACS: 61.05F-,62.65, 63.20.dd Keywords: neutron, ultrasound, mosaic,
time-of-flight, spin-echo
