Interstitial Loops in Neutron-irradiated Molybdenum

Abstract

NEUTRON irradiation at pile temperatures of the common metals such as copper¹, iron² or molybdenum³ has been found to produce very small prismatic dislocation loops as well as other strain centers on the limits of resolution. Metals subjected to charged particle or fission fragment irradiation, on the other hand, have been found to contain large prismatic loops^4,5 with diameters up to 1000 Å. In these latter experiments, it has been possible to prove that the loops are formed by the aggregation of interstitial atoms. Up to the present this has not proved possible with neutron-irradiated metals as the loops rarely exceed 1 or 200 Å in diameter, which makes application of the diffraction contrast method difficult, if not impossible. It has been inferred from annealing investigations that some of the larger loops (50–200 Å) in neutron-irradiated copper are interstitial, but direct confirmation is not yet available⁶. Experiments have recently been completed in these laboratories which established quite definitely that large dislocation loops, produced by neutron irradiation of molybdenum, are interstitial in nature.