Diffuse X-ray scattering measurements of point defects and clusters in iron

The nature of residual damage from atomic displacement cascades in iron has been investigated by diffuse X-ray scattering. A single crystal iron sample was irradiated at ∼60 °C in the High Flux Isotope Reactor at the Oak Ridge National Laboratory to a fluence of 1 × 1023 n/m2 (E > 0.1 MeV), or ∼0.01 dpa. Diffuse X-ray scattering measurements were carried out at the Advanced Photon Source at the Argonne National Laboratory on three specimens: unirradiated, as-irradiated, and irradiated and annealed for one hour at 450 °C (IA). The specimens were cooled to ∼40 K to minimize thermal diffuse scattering. Subsequent measurements of the specimen lattice parameter were completed at ORNL. The diffuse scattering in the as-irradiated specimen was dominated by interstitial defect clusters exhibiting a tetragonal distortion consistent with a 〈1 0 0〉 type defect. Substantial recovery of this defect component was observed following the anneal at 450 °C. A lattice parameter increase was observed following irradiation, which is also consistent with a substantial population of interstitial type defects. A net lattice parameter decrease was observed in the IA specimen, indicating loss of the interstitial defects with a residual population of vacancy-type defects.