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 hydrox yapatite over a temperature range of storage interest, taking into account a possible enhanced diffusion due to irradiation effects. The lanthanide io ns 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 d iffusion is shown and can be explained as a diffusion process governed by d efect migration towards the surface. Time resolved laser-induced fluorescen ce measurements show that, during enhanced diffusion performed under vacuum , the europium ions substitute the calcium ions preferentially in Ca(I) hyd roxyapatite sites. (C) 2000 Elsevier Science B.V. All rights reserved.