Crystal act as three dimensional grating with X-rays

• Since the wavelength of X-rays is in the order of 1 A° , ordinary grating which has 6000 lines per cm cannot produce an appreciable diffraction pattern of X-rays.
• Therefore, in the case of X-rays, instead of ordinary grating crystals gratings are used. In crystal grating atoms are arranged at lattice points in a regular fashion.
• These arranged atoms correspond to grating lines and the distance between two atoms is the grating element, in the order of le cm.
• The crystal grating differs from optical grating in such a way that in crystal grating, the atomic centres are not in one plane but are distributed in 3-dimensional space. But in optical grating, they are limited to one plane.
• Hence, crystal act as three dimensional grating with X-rays