The integral reflection coefficient <i>R</i> was measured for the (200) planes in LiF using a double crystal spectrometer over the wavelength range 0.7–2.1 A. For cleaved LiF, <i>R</i> was about 0.7 &times 10<sup>−4</sup> rads cornpared to 0.3 &times 10<sup>−4</sup> calculated for the theoretically perfect crystal case. After abrading with 15–20 μ carborindum, <i>R</i> increased to 2.90 &times 10<sup>−4</sup> at the 0.7-Å. end of the range and to 3.68 &times 10<sup>−4</sup> at the 2.1-Å end. For a flexed and reflattened crystal, R increased further to 9.45 &times l0<sup>−4</sup> at the 0.7-Å end of the range but was not improved over the abraded crystal a t the 2.1-Å end. Theoretical <i>R</i> values for mosaic graphite were compared with LiF. The value for graphite act 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 srich as LiF or by orienting powder crystallites as in the case of graphite.

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