X-ray diffuse scattering from neutron-irradiated uranium dioxide crystals

The distribution of the diffuse scattering intensity of uranium dioxide single crystals has been studied before and after irradiation by reactor neutrons with doses of 10^14, 10^15 and 5×10^16 fissions cm^-3. It has been found that irradiation effects occurred only at 5×10^16 fissions cm^-3. The {002}k planes of irradiated UO₂ and the {22 4̅}k and {11 3̅}k planes of unirradiated crystals have been observed as planes of high diffuse intensity. In unirradiated crystals the measured relative intensities around the 335 reciprocal-lattice point are in fair agreement with calculations using the Jahn formula, i.e. they have a maximum in the [33 1̅] direction. In irradiated samples, however, there exists a weak [002] maximum. This change in the distribution cannot be interpreted by Stokes–Wilson scattering alone and the extra intensity may be explained by the scattering of X-rays from defect modes of lattice vibrations.