Multiple reflections (MRs)—a new challenge for high-resolution neutron diffractometry and spectrometry

Multiple reflections mutually in dispersive diffraction geometry which can be realized in one bent perfect crystal (BPC) slab or by means of two BPC slabs of different cut used as a sandwich provide a monochromatic beam of excellent resolution parameters. In the former case, by testing several Si-crystal slabs of different cut we have found many intensive multiple diffraction effects in the thermal region which could be practically exploited for high-resolution monochromatization in neutron diffractometry or even in radiography. In the latter case of the sandwich we have found that a proper combination of two slabs can provide the monochromatic beam of any wavelength and the scattering angle. Depending on the bending radius of the crystal slab (or the sandwich of two slabs) the resolution Δλ/λ and the Δα collimation can be continuously adjusted in the range of 1×10−4–1×10−3. Of course, that the dispersive BPC elements can be used also for the high-resolution analysis of the scattered beam as well as for a high precision λ-calibration of e.g. TOF neutron scattering devices.