On possible exploitation of fully asymmetric diffraction geometry of bent perfect crystals for neutron monochromators in diffraction instruments

This paper summarizes recent results of an exhaustive experimental study on possible uses of bent perfect crystal (BPC) slabs of Si employed in the fully asymmetric diffraction (FAD) geometry. In all cases the FAD-BPC slab is employed as the second crystal of the dispersive double-crystal setting in combination with another BPC slab. The FAD geometry was tested in the output beam expansion (OBE) as well as in the output beam compression (OBC) diffraction orientations. A comparison of dispersive parallel (+n,-m) and antiparallel (+n,+m) settings was carried out with the FAD-BPC slab in the OBE orientation. High-resolution properties of the dispersive double-crystal settings are demonstrated by several experimental results, e.g. edge refraction or powder diffraction. Due to the given experimental conditions, for FAD geometry studies, we used Si(311) crystal planes having 29.5 degrees with respect to the main surface of the crystal slab.