The diffusion of La ions in hydroxyapatite was studied with regard to nuclear waste storage, and La and Eu were chosen to represent fission products and actinide elements. They were introduced into apatite targets by using ion implantation. An analysis of the evolution of profile distributions, as a function of annealing conditions, led to low values of the diffusion coefficients. A proposed explanation was that the La ions replaced Ca ions in the apatite structure and diffused through these positions. Time-resolved laser-induced luminescence measurements showed that Eu ions replaced Ca ions in both hydroxyapatite Ca(I) and Ca(II) sites. The 2 sites were probed by means of extended X-ray absorption fine structure measurements in order to elucidate the Eu environment.

Mechanisms Involved in Thermal Diffusion of Rare Earth Elements in Apatite. P.Martin, G.Carlot, A.Chevarier, C.Den-Auwer, G.Panczer: Journal of Nuclear Materials, 1999, 275[3], 268-76