We induced Co to form inclusions in Ag by ion implantation of Co into Ag and by coevaporation of both elements in a MBE system. Mossbauer spectroscopy at 4.2 K reveals the hyperfine fields present in the bulk and at the interface of the precipitates. By post-implanting the Co-57 activity into the coevaporated samples, we strongly enhanced this interface population, which facilitates the determination of the associated magnetic hyperfine field. The dependence of the precipitate size on the Co concentration and annealing treatment is monitored. We propose a simple model which allows to estimate the precipitate size in the case of preferential interface population.