X-ray diffractometer. X-ray diffractometry (XRD) is used to determine the constituents of a compound, particularly lattice structures in crystals. X-rays are fired at a sample and the angles of diffraction of the X-rays show the spacing and arrangements of the atoms within the sample. The resulting diffraction pattern may then be analysed, allowing researchers to determine the structure type and inter-atomic distances within the lattice. One famous use of the technique was on DNA (deoxyribonucleic acid) by Rosalind Franklin in 1953, which aided James Watson and Francis Crick in determining the unique helical structure of the molecule.