Beam-based positron annihilation spectroscopy has been applied to the study of near-surface vacancies created by 2 keV B+ ions implanted into Cz Si. The use of a controllable-energy positron beam means that the probe can be tuned to maximize the response to the subsurface damage. Time-dependent changes have been observed in the near-surface vacancy concentration profile. For example, after one week at room temperature, exposure of an implanted sample to white light for 1 h resulted in the migration of similar to95% of the measurable damage to sinks-primarily, it is assumed, to the surface. The relative importance of temperature, air, and light has been investigated.