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 temperature... »