Improving the Diffracting Properties of LiF: Comparison with Graphite

Abstract

The integral reflection coefficient R was measured for the (200) planes in LiF using a double crystal spectrometer over the wavelength range 0.7–2.1 Å. For cleaved LiF, R was about 0.7 × 10⁻⁴ rads compared to 0.3 × 10⁻⁴ calculated for the theoretically perfect crystal case. After abrading with 1.5–20 μ carborundum, R increased to 2.90 × 10⁻⁴ at the 0.7-Å end of the range and to 3.68 × 10⁻⁴ at the 2.1-Å end. For a flexed and reflattened crystal, R increased further to 9.45X10⁻⁴ at the 0.7-Å end of the range but was not improved over the abraded crystal at the 2.1-Å end. Theoretical R values for mosaic graphite were compared with LiF. The value for graphite at 1.66 Å was 4.5 times higher than that calculated for mosaic LiF and 1.3 times higher than the measured graphite values of Gould, Bates, and Sparks. It appears that one can approximate theoretical mosaic crystals by either distorting a nearly perfect crystal such as LiF or by orienting powder crystallites as in the case of graphite.