Abstract
An experiment was carried out to investigate the nature of residual damage from atomic displacement cascades in iron. Molecular dynamics simulations of primary damage formation indicate that many of the interstitials produced are contained in small glissile clusters with an activation energy for migration of ~0.1 eV, suggesting that most interstitials would be quickly lost from the material by absorption at sinks. 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 1x1023 n/m2 (E>0.1 MeV), or ~0.01 dpa. The irradiated sample was sectioned and one half was annealed for one hour at 450�C. Diffuse X-ray scattering measurements were then carried out at the Advanced Photon Source at the Argonne National Laboratory on three specimens: unirradiated, as-irradiated, and irradiated and annealed (IA). The specimens were cooled to ~40K to minimize thermal diffuse scattering. Subsequent measurements of the specimen lattice parameter were completed at the ORNL. The diffuse scattering in the as-irradiated specimen was dominated by interstitial defect clusters exhibiting a tetragonal distortion consistent with a <100> 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.
