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

The performance of elastically bent perfect (Si) and mosaic (Cu, Ge) m onochromator crystals is compared in the range of neutron wavelengths between 0.8 and 1.4 Angstrom in terms of neutron beam flux delivered a t sample position as well as in terms of resolution in powder diffract ion spectra recorded with an Al2O3 standard. The reflectivities of the mosaic crystals are found to be a factor 2-3 less than those predicte d by mosaic model calculations neglecting primary extinction. The elas tically bent Si crystals provide fluxes comparable or better than thos e of the germanium crystals of the same thickness. At the same time th eir effective mosaicity remains about three times lower, a fact that l eads to improved resolution in the high-angle part of the powder spect ra.