Scattering of X-Rays from Powdered Crystals at Low Temperatures

Jauncey has suggested that the true atom form factor of a crystal may decrease at low temperatures. With the method of Jauncey and Pennell, x-rays have been scattered from powdered crystals of KCl and NaF at various mean angles $\phi$ over a fairly wide range of $\frac{\left(sin\frac{1}{2}\phi \right)}{\lambda }$ at each mean angle $\phi$ with the powdered crystal first at 295°K and then at 103°K. Changes of the order of 1 or 2 percent in the intensity of the scattered rays were observed. Various possible explanations for this change are discussed. It is concluded that from 295 to 103°K the true atom form factors of NaF do not change, while those of KCl either do not change or decrease by very small amounts which are less than, but of the same magnitude as, those indicated in a recent paper by Harvey.