Diffusion under irradiation of rare earth elements in apatite

Nuclear waste ceramic forms among which the apatite, are under development as an alternative to waste glass in case of selective confinement. In that context, we studied the diffusion of lanthanide ions (La3+, Eu3+) in hydroxyapatite over a temperature range of storage interest, taking into account a possible enhanced diffusion due to irradiation effects. The lanthanide ions are introduced in apatite targets using ion implantation. The diffusion coefficients are deduced from Rutherford backscattering spectroscopy (RBS) at each step of annealing and irradiation procedure. Evidence of enhanced diffusion is shown and can be explained as a diffusion process governed by defect migration towards the surface. Time resolved laser-induced fluorescence measurements show that, during enhanced diffusion performed under vacuum, the europium ions substitute the calcium ions preferentially in Ca(I) hydroxyapatite sites.