Isochronal annealing study on n-irradiated single crystals and polycrystals of Mo

Positron annihilation techniques (PAT), both Doppler broadening and positron lifetime measurement methods, have been used to study the neutron-induced defects and their annealing behaviour in single crystals and polycrystals of Mo. Though both sets of samples were treated under similar irradiation and annealing conditions, striking differences were found in defect structures and annealing behaviour between single crystals and polycrystals. Grain boundary interaction with point defects needs to be considered as well as the effects of impurities. It is shown that the grain boundaries have a reducing influence on void nucleation and the growth of dislocation/vacancy loops not only during irradiation but also during post-irradiation annealing. The results have been discussed with a brief review of previous investigations. (author)