The interpretation of electron radiation damage in F.C.C. metals in terms of the conversion-two-interstitial model

Abstract

The present paper deals with the theoretical interpretation of the radiation damage and its recovery in f.c.c. metals. The relative merits of the one-interstitial and the conversion-two-interstitial model are discussed. It is concluded that only the conversion-two-interstitial model is able to account for all aspects of the experimental data presented in the literature. Since electron irradiation is expected to generate relatively simple defect structures and since copper has so far been investigated in most detail, emphasis is put on electron radiation damage in copper: Recovery substage I_E is demonstrated to be due to the free migration of metastable interstitials diffusing randomly in one dimension (presumably crowdions)'. The evidence that stage III is due to the annihilation of freely migrating 〈100〉-dumbbell interstitials at vacancies is shown to be very strong. Whereas in typical resistivity recovery studied after low-temperature irradiation the stage -III interstitials are produced by athermal conversion of crowdions, the pinning of dislocations during a γ-irradiation above room temperature reveals the thermal conversion of crowdions. The activation energy for thermal conversion is estimated to lie between 0.30 eV and 0.38 eV. Apart from individual features, the radiation damage in the other f.c.c. metals fits well into the pattern given above for copper. A noteworthy pecularity is that in the recovery of gold and (h.c.p.) cadmium free migration of a defect at low-temperatures could not be observed. In terms of the conversion-two-interstitial model this has the simple explanation that in these metals the activation energy for thermal conversion of the low-temperature interstitial is smaller than its migration energy.