Wavelength dependence of the reflectivity in neutron diffraction by perfect vibrating crystals

The neutron reflectivity of low-frequency vibrating nearly perfect crystals has been measured as a function of the neutron wavelength, the displacement field being parallel to the diffraction vector. In Bragg symmetrical geometry, the experimental results can be explained using a dynamical theory of diffraction by one-dimensionally distorted crystals [Guigay (1986). Acta Cryst. A42, 481-483]. In Laue symmetrical geometry, it is shown that it is necessary to distinguish the cases of very small and less-small amplitudes of vibration.