DIFFUSION AND RETENTION OF IMPLANTED HELIUM IN BERYLLIUM

Beryllium foils of 47 and 256 mum thickness were implanted homogeneously at room temperature with alpha-particles. The specimens were heated linearly to the melting point or isothermally at temperatures from 773 to 1173 K. Diffusion coefficients were derived from the kinetics of helium desorption. Even at 1173 K only a small fraction of the implanted helium was released while the major part was retained up to temperatures close to the melting point. In a second experiment beryllium foils were implanted to a certain depth at elevated temperature and helium evolution was recorded during implantation. In this experiment the released helium flux rose within a few seconds to a constant value which amounted from above 10% to below 0.1% of the incoming flux, depending on the distance of the implantation region from the surfaces.