Dislocation loops in neutron-irradiated copper

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Abstract
Electron transmission microscope observations have been carried out on copper irradiated with neutrons at temperatures of 35°c and 60°-100°c, and subsequently thinned by electropolishing. Specimens irradiated to a dose of 6.7 × 1017 cm−2 (at 35°c) contain ∼3 × 1016 defects c.c.−1 in the form of small regions of strain (average diameter ∼75 Å), some of which can be resolved as dislocation loops. With increasing dose of irradiation (5.6 × 1018, 1.4 × 1020n cm−2) many more of the defects can be rocognized as loops, and their average diameter increases to ∼150 Å and ∼ 300Å respectively. The dislocation density in the form of loops is 1010−1011 cm−2 The stability of the loops and their behaviour on annealing are as expected from prismatic loops. The loops are considered to nucleate as a result of the collapse of dises of vacancies produced by vacancy clustering in the central region of a displacement spike, and to grow by migration of vacancies or of vacancy clusters. Radiation hardening is interpreted in terms of the large density of dislocations in the form of loops. The hardening anneals out at the same temperature at which the loops are observed to disappear by climb.