Ion beams in the MeV energy range impinging on solid materials are stopped in surface layers usually few micrometers thick, with a depth profile depending on the beam energy modulation. Using radioactive ions to bombard materials belonging to parts undergoing friction, and then monitoring the intensity of the emitted γ-radiation, we have succeeded in determining the wearing speed. Sub-micrometric wearing of parts working for periods of several months can be monitored implanting ions of the low radio-toxicity ⁷Be, with a half life of 53 d, detecting the characteristic 478 keV γ-ray line. This not only allows to study the wearing properties of different materials, but also to reveal the status of hidden parts during operation in view of possible replacements that could be needed.