The arcing of X-ray diffraction spots in X-ray photographs from cadmium iodide crystals

The X-ray diffraction photographs from cadmium iodide crystals exhibit extension of diffraction spots in directions nearly perpendicular to the c* axis. The reason for this extension (termed arcing) is not well understood. It has been shown in this communication that the arcing in cadmium iodide crystals may arise as a result of paracrystalline distortions introduced during the growth of crystals. Evidence and arguments have been advanced to show that whereas the arcing phenomenon cannot be explained on the basis of the presence of lattice defects, it can be readily explained on the basis of the presence of paracrystalline distortions.