A medium-resolution double-crystal diffractometer for the study of small-angle neutron scattering

The angular resolution of the parallel (1, −1) double-crystal setting has been relaxed from the original value of 10 μrad for perfect silicon crystals into the region 0.1–1 mrad by their elastic deformation. The totally reflecting region of the dynamical diffraction curve is broadened proportionally to the deformation while the wings as well as the diffuse scattering intensity are not affected substantially. This experimentally verified fact causes gain both in intensity and the signal/noise ratio. First experiments were performed with bent Si single-crystal bars in symmetric 220 reflection geometry at θ_B = 16.7°. With bending radii of the order of 100 m, angular resolution 0.6 mrad and an effective neutron flux at the sample position of 400 mm⁻² s⁻¹ were achieved. These values do not depend on beam cross section.