Crystal structure is explored through the diffraction of waves having a wavelength comparable with the interatomic spacing $\left(10^{-10} \mathrm{~m}\right)$ in crystals. Radiation of longer wavelength cannot resolve the details of structure, while radiation of much shorter wavelength is diffracted through in conveniently small angles. Usually diffraction of X -rays is employed in the study of crystal structure as X-rays have wavelength comparable to interatomic spacing.