MOSAIC LIH MONOCHROMATORS FOR LOW-ENERGY X-RAYS

Mosaic LiH is evaluated for use as an X-ray monochromator. The theoretical performance of mosaic LiH is compared to that of LiF, graphite and other mosaic crystals. Calculations are made for Cu K-alpha radiation (8.04 keV) and at the U M(IV) edge (3.728 keV). For large single crystals of LiH and LiF, experimental measurements at 8.04 keV are reported for the integrated reflectivity, mosaic spread and strain/particle-size-limited resolution. Although the LiH crystal had a nonuniform mosaic spread and was partially transparent to the 8.04 keV incident X-rays, the integrated reflectivity exceeded by 25% that of a mosaic LiF crystal measured under identical conditions. Longitudinal theta-2-theta scans through the LiH(200) reflection showed that the peak width is less than that of a perfect Si(220) crystal. The X-ray properties of mosaic LiH are extrapolated to low X-ray energies; in this regime the small photoelectric absorption coefficient makes LiH even more attractive as an X-ray monochromator crystal.