Layers of cavities in silicon produced by He implantation are a promising tool to prevent residual impurities, mainly transition metal atoms, to interact with implanted dopant atoms. The γ-γ perturbed angular correlation (PAC) technique is well suited to study the behaviour of implanted impurity atoms during thermal treatments of the samples, since from quadrupole interaction frequencies observed with PAC a detailed picture of the lattice environment of the probe can be derived. In the present study, the PAC probe 111In was used to investigate the cavity formation in Si after the implantation of He and Ar and the interaction between impurities and cavities during and after their formation process. It is found that the PAC probe is trapped in the cavities and quadrupole interaction frequencies corresponding to probes situated on the inner surfaces of the cavities can be observed. The efficiency of the cavities as transition metals getters was studied by implanting shallow profiles of Au, Ag or Cu not overlapping the cavity layer. The trapping of these impurities in cavities containing PAC probes was signalled by a characteristic modification of the PAC signal.