Thermal diffusion of molybdenum in apatite

One of the solutions to store high level nuclear wastes (actinides and fission products) is deep geological repository. Since some of these radionuclides have extremely long half-lives, they require an appropriate durable immobilisation system. Several materials, including apatites, are studied as potential 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 filiation. Therefore, we focused on the migration study of molybdenum in hydroxyapatite Ca-10(PO4)(6)(OH)(2). Molybdenum was introduced by ion implantation, 40 nm deep, in pellets of hydroxyapatite. Then the samples were heated under air. The evolution of the molybdenum profiles after each annealing step was followed by Rutherford backscattering spectroscopy (RBS), showing a volatilization of molybdenum. Moreover, XPS analysis made on molybdenum led us to think that the volatile species formed is MoO3. (C) 2000 Elsevier Science B.V. All rights reserved.