The number of scattering centres measured using channeled particles passing through a cavity layer formed by He implantation in silicon is shown to depend on the probe energy. This unusual result is explained in terms of interaction of channeled particles with atoms of cavity walls and dislocation lines. The Rutherford backscattering analysis in channeling incidence (RBS-C) is then used to study the time evolution of cavity and dislocation populations during annealing. It is shown that cavities are actually bubbles in equilibrium with the silicon matrix. The time to reach this equilibrium is related to the gas desorption. For our experimental conditions (40 keV, 5 × 1016 cm−2 and 800 °C), this equilibration time is about 10 minutes. Strain and dislocation build-up occur under shorter time scales, during which bubbles are probably overpressurized. The pinning of bubbles at dislocations must be taken into account to explain the evolution of these extended defects over a longer period.