Why only x rays are used for study of crystal structure?

Actually cystal is a three dimensional grating with grating element(interplanar spacing)as of the order of 1 angstron unit. Also the wavelength of X rays is of the order of 1 angstron which satisfies basic condition of diffraction(Bragg's law). Gamma rays are not used for the same reason as well as gamma ray production is not high enough, difficult to focus and high intense enough to create particl and antiparticle.