Thermal annealing of the E(c) - 0.18 eV level in Czochralski-grown sil
icon crystals irradiated by Co-60 gamma rays has been investigated usi
ng Hall effect measurements. An anomalous annealing kinetics has been
found, in which the centre disappearance probability is increased with
isothermal annealing time. A tentative kinetic model of the process i
s proposed.