The lifetimes of excess carriers in phosphorus‐doped, float‐zoned silicon were measured before and after irradiation by cobalt‐60 gamma rays. Recombination in the samples prior to irradiation was dominated by a donor‐like recombination center located 0.13 eV above the valence band. After irradiation, two recombination centers were found in the samples: one located atEc‐0.17 eV and the other atEc‐0.40 eV. The center atEc‐0.17 eV can be identified with the oxygen‐vacancy defect (Si‐Acenter), but no positive identification of theEc‐0.40 eV center can be made. By assuming that theEc‐0.40 eV center is the phosphorus‐vacancy complex, the hole capture cross section of the center was estimated as 9 × 10−14cm2.