Interference effects in dynamic neutron diffraction under conditions of ultrasonic excitation

Results are presented of a theoretical and experimental study of a novel type of pendular beating effect manifest in the diffraction of hard radiation under conditions of ultrasonic excitation. The dependence of the scattering intensity I for thermal neutrons on the sound amplitude w in a Si single crystal is measured. Oscillations of the intensity I(w) which are related to the appearance of additional gaps on the dispersion surface and also oscillation of the mean slope of the I(w) dependence on rotation of the sample around the reciprocal lattice vector are observed. It is shown that near the frequency threshold the oscillation contrast and the mean slope of I(w) are determined by the parameter cos(δqT), where δq is the shift of the neutron dispersion surface on switching on of the ultrasound and T is the crystal thickness. The experimental data are in agreement with the theoretical calculations