Study of damage rate decrease of lead irradiated with 25 MeV oxygen ions at 7.2 K

Stage II damage rates of lead films have been measured after irradiation with 25 MeV oxygen ions at 7.2 K. The thickness of the samples of 3 μm is smaller than the projected range of 11 μm. The damage rates decreased by three orders of magnitude due to increasing Frenkel pair concentration. A model proposed by Lueck and Sizmann fits the experimental data reasonably well over a wide range of defect concentration. It is shown that for defect concentrations c > 10-4 spontaneous recombination processes play a major role in the defect production, whereas free migration of defects is of less importance. The extrapolation of the damage rate to zero seems questionable due to the lack of an appropriate damage rate formula for high defect densities. The annealing behaviour of the irradiated lead samples is compared to that found after irradiation with electrons, deuterons, and neutrons. (author)