The annealing of radiation damage in tungsten investigated by field-ion microscopy

Abstract

Annealed tungsten wire has been reactor-irradiated to a dose of 10 17 n. v. t. ( > 1 MeV), and specimens for field-ion microscopy prepared from the wire. Vacancies could be identified in certain regions of the field-ion microscope image, and the size and shape of small clusters of vacancies could be found by careful field-evaporation. Using the field evaporation technique the clustering of vacancies has been followed in specimens that were unirradiated, irradiated, and given certain post-irradiation heat treatments. The only interstitial defects seen arose from impurities. Specimens examined after being annealed in stage III ( ~ 400°C), showed fewer single vacancies, and there was a simultaneous increase in the number of small vacancy clusters. It is concluded that stage III annealing in tungsten may be associated with the migration of single vacancies to small clusters, rather than the migration of an interstitial defect.