Neutron irradiation damage in molybdenum

Abstract

An electron microscope study has been made of the time-dependent annealing behaviour of interstitial loops in impure and pure molybdenum neutron-irradiated at 77°K (A₇₇ and C₇₇) respectively and of vacancy loops in pure molybdenum neutron-irradiated at 473°K (C₄₇₃). The results have been quantitatively analysed and loop growth behaviour has been compared with that predicted theoretically for perfect loops growing by bulk vacancy-limited diffusion mechanism and by a glide and self-climb mechanism. It has been shown that the interstitial loop growth observed in A₇₇ and C₇₇ is accounted for by a glide and self-climb mechanism. On the other hand, vacancy loop growth observed in C₄₇₃ can be accounted for by a bulk vacancy diffusion mechanism although it is considered that both mechanisms contribute to the observed growth at intermediate stages of the anneal. Finally, two general distinguishing features of loop growth have been exposed. Firstly, under bulk vacancy diffusion-limiting conditions, interstitial loops are considerably more stable than vacancy loops whereas the glide and self-climb mechanism makes no distinction between loop nature. Secondly, with regard to the growth kinetics, bulk diffusion-limited growth is approximately linearly dependent on time t, whereas growth by glide and climb should follow a t ²/13 law.