Positron implantation depth profiles in alpha-irradiated 18 carats gold

Positron implantation profiles have been investigated over a range of about 1 m on a gold solid solution containing 40 at.% of Ag, after helium implantation at 300 keV. The S parameter lineshape of the annihilation radiation, sensitive to both the size and the concentration of vacancy type defects, was measured after isochronal annealing up to 930 K. Depending on the incident energy of the positron, i.e. the distance between its mean implantation depth and the helium concentration maximum, several recovery stages were unambiguously observed attributed, respectively, to free vacancy migration (I), helium stabilization of larger defects (II) and competitive processes of bubble nucleation (III) and breaking up (IV). These latter mechanisms lead to the observation of a lineshape maximum at T=0.5Tm (melting point), already observed for nickel.