COMPARATIVE TESTS OF NEUTRON MONOCHROMATORS USING ELASTICALLY BENT SILICON AND MOSAIC CRYSTALS

The performance of elastically bent perfect (Si) and mosaic (Cu, Ge) monochromator crystals is compared in the range of neutron wavelengths between 0.8 and 1.4 Angstrom in terms of neutron beam flux delivered at sample position as well as in terms of resolution in powder diffraction spectra recorded with an Al2O3 standard. The reflectivities of the mosaic crystals are found to be a factor 2-3 less than those predicted by mosaic model calculations neglecting primary extinction. The elastically bent Si crystals provide fluxes comparable or better than those of the germanium crystals of the same thickness. At the same time their effective mosaicity remains about three times lower, a fact that leads to improved resolution in the high-angle part of the powder spectra.