X-ray wavelength in the same electromagnetic waves and light refers to a thing of about 0.01 ~ 100Å. The X-ray diffraction, is often used ones of the wavelength of these 0.1Å ~ number Å. Crystal atoms are periodically arranged, it constitutes a spatial grating, the period is usually several to several ten Å. When X-rays in the cycle and equal to or shorter wavelength is incident on the crystal, a strong X-rays are observed in a specific direction, resulting in diffraction phenomena. It is the crystal lattice becomes diffraction grating, the optical path difference of X-rays that are scattered at each position, when being an integral multiple of the wavelength of X-rays,