Abstract
Nickel specimens have been homogeneously implanted with helium ions at about 325 K to a total dose of 500 appm. Distinct defect structures are observed in the irradiated specimen during isochronal annealing. Positron lifetime and Doppler broadening techniques were applied to study the evolution of the defect configurations. The influence of helium on the positron annihilation characteristics is clearly visible. The nucleation of helium bubbles could be determined. At higher annealing temperatures two distinct positron bound states are found. For both states the temperature dependence of the annihilation characteristics is similar to that reported for voids. Clear differences in the annihilation parameters have been established for empty and helium-decorated vacancy clusters.
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