Simulation of the α-annealing effect in apatitic structures by He-ion irradiation: Influence of the silicate/phosphate ratio and of the OH −/F − substitution

In fluoroapatite, the α-annealing is a crystal recovery process due to the electronic energy loss of α-particles emitted by radionuclides. This effect, which can be accompanied by a thermal recovery, is accounting for the crystalline state of natural calcium phosphate apatites containing long lifetime actinide isotopes. The aim of the present study is to determine the influence of the silicate–phosphate grouping substitution, on the α-annealing efficiency. In addition, measurements have been performed on hydroxyapatite Ca 10(PO 4) 6(OH) 2 and compared with those obtained on fluoroapatite Ca 10(PO 4) 6F 2 to evaluate the influence of the OH −/F − substitution on the annealing efficiency. Using a transmission electron microscope (TEM) on line with an ion implanter, the main result obtained in this study is that α-annealing is strongly dependent on the chemical composition of the mineral. Our results show that this effect is decreasing when the SiO 4/PO 4 ratio increases and when F − is substituted for OH − anions.