BENT PERFECT CRYSTALS IN ASYMMETRIC DIFFRACTION GEOMETRY IN NEUTRON-SCATTERING EXPERIMENTS

Asymmetric cuts of elastically deformed perfect crystals, although less frequently used in practice, may also be attractive for applications. They offer an additional degree of freedom for optimization of instruments setups in terms of real- and reciprocal-space focusing. Some aspects of an useful employment of cylindrically bent perfect Si crystals in a strongly asymmetric geometry in neutron scattering experiments are presented. Special attention is paid to the limiting case of the fully asymmetric diffraction (FAD) geometry of the bent crystals. Here the absence of real-space focusing (the focus is directly at the crystal) is compensated by the effective mosaicity controlable in a large range, permitting to design instrument configurations offering considerably higher resolution for a given luminosity than the mosaic crystals.