Phenomenon in which the crystal , by virtue of their uniform spacing, cause an interference pattern of the waves in an incident beam of X rays .
The crystal's atomic planes act on the X rays in the same way a uniformly ruled grating acts on a beam of light (see polarization ). The interference pattern is specific to each substance and gives information on the structure of the atoms or molecules in the crystal. See also {{link=Bragg, Sir William Henry">William Henry Bragg .