Positron Annihilation Lifetime at Defects in Metals

Since positron annihilation measurement is very useful to the study of defects in solids, many investigations have so far been performed for various crystals, especially metals and alloys. Atomic and electronic structures of various defects are, however, very complicated and have not been fully clarified yet and more detailed experiments and precise calculations are still needed. Vacancy and its clusters, dislocations and precipitates are main objects so far investigated and in this paper recent experimental and calculational results for vacancies in Fe and Fe-alloys and dislocations in Ni and Fe are described. Positron annihilation lifetime measurements for high-purity Fe and Fe-alloys irradiated with electrons at low temperature showed the fundamental behaviour of vacancies and the interaction between a vacancy and alloying elements, It was made clear that vacancies in Fe become mobile above 200K in Fe, but in the presence of various alloying elements the interaction behaviour between vacancies and alloying elements became important. Deformed Ni and Fe usually showed intermediate lifetime component between matrix and a vacancy. Positron lifetime calculation showed that this intermediate lifetime component does not correspond to a straight dislocation, but vacancies trapped at dislocation lines