The annealing of dislocation loops in neutron irradiated copper

Abstract

Transmission electron microscopy has been used to measure the density of defect clusters and loops of various sizes in neutron irradiated copper as a function of annealing. Quantitative measurements show that recovery occurs at ∼ 300°c in two stages. In the first of these the density of the larger clusters (> 50 Å diameter) is greatly reduced, the process occurring in a few tens of minutes at 275°c with an apparent activation energy of ∼ 1 ev. In the second stage of recovery, which occurs in several thousand minutes at 275°c, the small clusters (< 50 Å diameter) and the remaining larger loops disappear with an apparent activation energy of ∼ 2 ev. The first stage is attributed to the thermal dissociation of sub-microscopic vacancy clusters and the consequent annihilation of a large proportion of the interstitial atoms present in the larger loops. Also in this stage the larger vacancy clusters increase in size and stability. The second stage is the dissociation of these larger vacancy clusters and the annihilation of the remaining interstitial loops. The shape of the loop size distribution can be predicted throughout the annealing by a simple model in which each interstitial loop, irrespective of size, collects the same number of vacancies during a given anneal.