Identification of the nature of neutron-irradiation-induced defects in copper by means of electron irradiation

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Abstract
Identification of the nature of small point defect clusters introduced in copper by neutron irradiation was made based on the behavior of the analyses of the defect clusters under electron irradiation in a high voltage electron microscope. The point defect clusters examined were those produced in thin foil and bulk specimens by three neutron irradiation facilities at temperatures between 300 and 473 K: a fusion neutron source RTNS-II (mono-chromatic 14MeV), a fission reactor JMTR (up to 2 MeV) and a spallation neutron source LASREF (up to 100 MeV). The electron irradiation using a high voltage electron microscope was performed with 1 MeV electrons at 300 and 473 K. About 95% of the clusters in the thin foils and 85% in the bulk samples were identified to be of the vacancy type. Fewer vacancy clusters and more interstitial type dislocation loops were observed in the bulk specimens than in the thin foil specimens. There were some differences in the defect structures between the different neutron irradiation facilities; the proportion of interstitial type clusters introduced by JMTR irradiation was less than those by RTNS-II and LASREF. The judgment validity of the nature of the defect clusters from electron microscope images was examined from the results of the present additional electron irradiation.