Positron annihilation studies on alpha-irradiated and deformed niobium

Positron lifetime and annihilation lineshape measurements have been made to study the defect kinetics and He-vacancy interactions in alpha-irradiated Nb. A comparative study on plastically deformed Nb has also been performed. The isochronal annealing results are discussed with a brief review of previous investigations. Dislocation/vacancy loops annealing occurs above 7000C. Positron trapping rate at He-vacancy clusters is seen to increase with the addition of He atoms to the clusters. Results favour the idea of He-bubble growth by an addition of He atoms or vacancies at intermediate temperatures (350-7500C) and by bubble migration and coalescence at high temperatures (800-9000C). Annealing out of He-bubbles/He-vacancy complexes is seen above 9000C. (orig.)