Effect of Thermal Vibrations on Diffraction from Perfect Crystals. II. The Bragg Case of Reflection

It has been experimentally verified in the case of symmetric Bragg reflection from perfect crystals of silicon that integrated intensities decrease as $\exp \mathrm{}(-M)\mathrm{}$ with increasing temperature. The usual Debye-Waller factor is $\exp \mathrm{}(-2M)\mathrm{}$ for mosaic crystals. It has been demonstrated to a significance level of 1.5%, that the intrinsic width of a perfect crystal diffraction maximum is smaller at elevated temperatures, i.e., there exists a thermal narrowing. It is concluded that thermal motion does not affect perfect crystal diffraction in the Bragg case as an imperfection.