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

In fluoroapatite, the a-annealing is a crystal recovery process due to the electronic energy loss of alpha -particles emitted by radionuclides. This e ffect, which can be accompanied by a thermal recovery, is accounting for th e crystalline state of natural calcium phosphate apatites containing long l ifetime actinide isotopes. The aim of the present study is to determine the influence of the silicate-phosphate grouping substitution, on the alpha -a nnealing efficiency. In addition, measurements have been performed on hydro xyapatite Ca-10(PO4)(6)(OH)(2) and compared with those obtained on fluoroap atite Ca-10(PO4)(6)F-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 alpha -annealing is strongly dependent on the chemical composition of the mineral. Our results show that this effect is decreasing when the SiO4/ PO4 ratio increases and when F- is substituted for OH- anions. (C) 2001 Pub lished by Elsevier Science B.V.