High energy cascades in gold as studied by high energy self-ion irradiation

Primary knock-on atom (PKA) energy spectrum extends up to several hundreds of keV in fusion reactor materials irradiated with 14 MeV neutrons. When we are going to evaluate materials behavior in an expected d-Li type intense neutron source, fundamental knowledge on effects of high energy PICA on for mation of cascade damage, microstructural evolution and properties of irrad iated materials is required. In this study, 170 MeV self-ion irradiation of thin foils of gold were performed to estimate effects of very high energy PKA on formation of defect clusters by cascade damage and its interactions. Defect clusters of vacancy type were observed in the thin foils of gold ir radiated to 5 x 10(13)-1 x 10(15) ions/m(2). In the case of irradiation wit h 170 MeV self-ions of which the projected range exists at 6.3 mu m from th e ion incident surface, films of gold, 1.1, 3.0, 4.3, 6.3 and 7.2 mu m in t hickness, were placed in front of the 50 nm thick specimens to change PKA e nergy spectrum within the specimens. The number of vacancy clusters within a cluster group formed by a PKA varied with the thickness of gold film. Hig h energy PKA was found to increase the number of defect clusters. However, size distributions of defect clusters were not strongly dependent on PKA en ergies. Interactions of high energy cascades result in the appearance of ne w defect clusters near the existing defect cluster groups in the higher dos e range. Dose dependence of defect cluster density was similar to that obse rved in 14 MeV and fission neutron irradiated specimens. The contribution o f PKA higher than 400 keV to the interactions of cascades is estimated from the calculated PKA energy spectrum and low energy self-ion irradiation dat a. (C) 1999 Elsevier Science B.V. All rights reserved.