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X-rays are electromagnetic radiation of wavelength about 1 A (10-10 m). They are found in that portion of the electromagnetic spectrum between gamma and ultraviolet rays. As a result of the discovery of X-rays, in 1895, scientists were able to probe crystalline structure at the atomic level. X-ray diffraction has been used for both the fingerprint characterization of crystalline materials and the determination of their structure. Each crystalline solid has a unique characteristic X-ray powder pattern that may be used for identification purposes. Once the material has been identified, X-ray crystallography may then be used to determine the structure. The structure relates how the atoms pack together in the crystalline state and what the inter-atomic distance and angles are. X-ray diffraction is used in solid state chemistry and can determine the size and shape of the unit cell for any compound using the diffraction of X-rays. Diffraction patterns are governed by the Bragg equation.