Direct Observation of Radiation Damage In Molybdenum

Abstract

The primary objective of the research is to study the effect of neutron irradiation, both at ambient and elevated temperatures, on the structure of molybdenum, and to compare and contrast with previous observations on copper and nickel. The defect structures produced by neutron irradiation at doses up to approx. 10²⁰ nvt, at temperatures from ambient to 600°C, are being studied using transmission electron microscopy. For low doses approx. 10¹⁸ nvt at 600°C, large prismatic dislocation loops (average diameter 1100 A) were observed on planes approximately parallel to 111, and having the normal slip vector 1/2 < 111>. Diffraction contrast experiments were carried out on these loops which proved conclusively that these were formed by the collapse of interstitial aggregates. By comparison, ambient temperature irradiation to this dose level produced a structure with a high density of spots which were not readily resolvable as loops. Specimens have also been irradiated to approx. 10²⁰ nvt at ambient temperature and have been found to contain a higher density of the unresolved damage. The mechanism of the formation of the loops and their interaction with glide dislocations is discussed.