Radiation effects in plutonium and carbonate co-doped calcium hydroxy apatite: An EPR study

Electron paramagnetic resonance studies were conducted on synthetic calcium hydroxy apatite samples co-doped with ²³⁹Pu and carbonate ion. These investigations were carried out to assess the self-irradiation effects in bone and teeth on exposure to plutonium, as calcium hydroxy apatite is the major constituent of bone and teeth. On self-irradiation, in addition to the signal from O^- ion arising from the radiolysis of hydroxide ion, EPR signals due to CO₂^-, PO₂^2- and another signal assigned to surface O^- ions were observed in the samples. In freshly quenched gamma irradiated samples, signals from CO₃^-, O^- , PO₂^2- and O₂^- ions were observed. The EPR signal of O₂^- ion shows a doublet splitting suggesting that O₂^- ion gets preferentially stabilized close to Pu⁴⁺. The radiation damage due to Pu⁴⁺ at Ca²⁺ sites, in the sample appears to be lower as compared to that due to external gamma-irradiation. Moreover, the alpha-dose in ²³⁹Pu doped samples has self-annealing effects. These are attributed to localized radiation damage due to alpha-particles compared to evenly distributed radical ions produced due to gamma-irradiation.