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 Kα 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 θ–2θ 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.