Identification of the nature of small point defect clusters in neutron irradiated Fe-16Ni-15Cr by means of electron irradiation

The nature of very small point defect clusters in Fe-16Ni-15Cr irradiated with fission neutrons was identified from their behavior under electron irradiation with a high voltage electron microscope. In this analysis, the defect clusters which grew during electron irradiation were judged to be of interstitial (I)-type and those which shrank or disappeared to be of vacancy (V)-type. The fraction of the number of I- and V-type defect clusters in a specimen irradiated as a bulk at 353 K were found to be 7% and 93%, respectively. In a specimen irradiated at 623 K as a bulk, most of defect clusters were I-type with a very small fraction of V-type. In a thin foil specimen irradiated at 573 K, the fraction of I-type defect clusters increased from 20% near the thin specimen edge to 70% at a thicker part of 120 nm. These results were consistent with those in the previous judgement from the shape and contrast of transmission electron microscope image.