The analysis of crystals by the X-ray spectrometer

Abstract

In a former communication to the Royal Society, an attempt was made to determine for certain crystals the exact nature of the diffracting system which produces the Laue X-ray diffraction photographs. The crystals chosen for particular investigation were the isomorphous alkaline halides NaCl, KCl, KBr, and KI. As in the original experiments of Laue and his collaborators, a thin section of crystal was placed in the path of a narrow beam of X-rays, and the radiation diffracted by the crystal made its impression on a photographic plate. By noticing what differences were caused in the photograph by the substitution of heavier for lighter atoms in the crystal, a definite arrangement was decided on as that of the diffracting points of the crystalline grating. Though it was found possible in the case of these simple salts to determine the position of the atoms of alkaline metal and halogen, which constitute the elements of the dimensional diffraction grating, yet this method, which may be called the photographic method, is very limited in its range of applications. It was only the extremely simple nature of the NaCI structure which made its analysis possible. On the other hand, the X-ray spectrometer, which has been devised by W. H. Bragg for the purpose of studying the reflection of X-rays by crystals, affords a very much more powerful method of research into the structure of the crystal.