Neutron reflection properties of Si(111) single crystals for application in a backscattering spectrometer: a systematic approach

A systematic study has been conducted to evaluate the performance of spherically bent Si(111) single crystals to be harnessed as the analyser components in neutron backscattering spectrometers. Si(111) crystals with different characteristics, in terms of growth method, surface treatment and thickness, were selected and analysed. Crystal manufacturing features drive differences in the reflecting spectra of the elastic peak. Additionally, the reflecting properties of the optical component, in terms of energy resolution and intensity, display univocal trends with the crystal thickness. The increase in the bent Si(111) crystal thickness conveys a monotonic increase in the neutron reflection yield and a relaxation of the energy resolution values; however, the total neutron reflection shows a changing trend above 1 mm thickness in which there is no significant improvement in the neutron reflected intensity for a bending radius of 2 m. This behaviour is relevant for the selection of the analyser crystal, providing invaluable insight into the design of future high-resolution crystal spectrometers, such as MIRACLES, the near-backscattering spectrometer being built at the European Spallation Source.