Physics: Clark and Duane Further Experiments upon the Reflection by a Crystal of Its Characteristic X-rad[ation

During the development of a new method of analyzing crystals by X-rays we discovered that the X-rays characteristic of and excited in the chemical elements in a crystal are reflected by the crystal itself. The reflection takes place both in accordance with the Bragg law: nX = 24 sin 0 and. also in an anomalous fashion. The ionization spectrometer utilized in these investigations and the various steps in the method of analyzing crystals have already been described in detail.' From the spectra of the normally reflected X-rays characteristic of the constituent elements in the crystal we have been able to determine accurately the spatial distribution of the atoms in the crystal lattices of potassium iodide, cesium iodide, potassium tri-iodide, cesium tri-iodide and cesium dibromo-iodide, and to distinguish clearlv between planes containing iodine and cesium atoms in spite of the nearly identical reflecting powers.