Thermal diffusion of molybdenum in apatite

One of the solutions to store high level nuclear wastes (actinides and fiss ion products) is deep geological repository. Since some of these radionucli des have extremely long half-lives, they require an appropriate durable imm obilisation system. Several materials, including apatites, are studied as p otential inertial matrices. One of the most fed long life fission isotopes, Tc-99 (half-life t(1/2) =2 x 10(5) yr) is produced by the Mo-99 --> 99Tc f iliation. Therefore, we focused on the migration study of molybdenum in hyd roxyapatite Ca-10(PO4)(6)(OH)(2). Molybdenum was introduced by ion implantation, 40 nm deep, in pellets of hy droxyapatite. Then the samples were heated under air. The evolution of the molybdenum profiles after each annealing step was followed by Rutherford ba ckscattering spectroscopy (RBS), showing a volatilization of molybdenum. Mo reover, XPS analysis made on molybdenum led us to think that the volatile s pecies formed is MoO3. (C) 2000 Elsevier Science B.V. All rights reserved.