Unlike the usual diffraction by a stationary object, neutron diffraction on a running wave is an essentially non-stationary process resulting in transfer of energy ΔE=nℏΩ to the neutron. Here Ω is the wave frequency, ℏ is the Planck constant, and n is an integer.

The report will briefly give the theory of neutron diffraction on traveling and standing SAWs and present the results of experiments on the study of neutron diffraction on ultrasonic waves moving both along and against the direction of the neutron wave, as well as on a standing SAW. In one of them, measurements were conducted with a fixed neutron wavelength and a variable incident angle. The second experiment was done at a fixed incident angle in TOF mode for a wide range of wavelengths.

SAW arise due to periodical oscillation of the near-surface layer of matter that moves with alternative velocity and acceleration. For a SAW with a frequency of tens MHz this acceleration reaches a value of 10⁷g. Since the theory of neutron diffraction by a surface wave is based on the concept of the effective potential of matter, comparison of the experimental data with the calculation is a sensitive test of the validity of this concept in the case of large accelerations.