Thermal diusion of molybdenum in apatite C. Gaillard a, * , N. Chevarier a , N. Millard-Pinard a , P. Delich ere b , Ph. Sainsot c a Institut de Physique Nucl eaire de Lyon, IN2P3/CNRS, Universit e Claude Bernard, F-69622 Villeurbanne cedex, France b Institut de Recherche sur la Catalyse, F-69622 Villeurbanne cedex, France c Institut National des Sciences Appliqu ees, F-69621 Villeurbanne cedex, France Abstract One of the solutions to store high level nuclear wastes (actinides and ®ssion 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 ®ssion isotopes, 99 Tc (half-life t 1=2  2 ´ 10 5 yr) is produced by the 99 Mo ® 99 Tc ®liation. Therefore, we focused on the migration study of molybdenum in hydroxyapatite Ca 10 (PO 4 ) 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 pro®les after each annealing step was followed by Rutherford backscattering spectroscopy (RBS), showing a volatilization of molybdenum. Moreover, XPS analysis made on mo- lybdenum led us to think that the volatile species formed is MoO 3 . Ó 2000 Elsevier Science B.V. All rights reserved. PACS: 61.10.CB Keywords: Apatite; Molybdenum migration; Ion beam analysis 1. Introduction The crystal structure of apatite allows a wide range of anion and cation substitutions [1]. Apa- tites are widely studied as potential inertial ma- trices to actinides and some long lived ®ssion products con®nement. In this work, we focused on the diusion of molybdenum in hydroxyapatite, which is spontaneously synthesized during condi- tioning of radioactive ashes in cement [2]. The radioactive ashes, which originated from the nu- clear fuel reprocessing, contain ®ssion products among which the widely fed molybdenum isotope 99 Mo, which leads by b  emission to the long lived 99 Tc t 1=2  2  10 5 yr). Previous works [3,4] have shown that the hydroxyapatite structure is able to accommodate a variety of univalent, divalent, tri- valent cation substitutions among which those of lanthanide and actinide ions. To our knowledge, no data are available on the behavior of molyb- denum in hydroxyapatite but this element is known to precipitate under metallic form in UO 2 [5]. The study of molybdenum migration in hy- droxyapatite was performed using the comple- Nuclear Instruments and Methods in Physics Research B 161±163 (2000) 646±650 www.elsevier.nl/locate/nimb * Corresponding author. Tel.: +33-4-72-43-10-63; fax: +33- 4-72-44-80-04. E-mail address: cgaillar@ipnl.in2p3.fr (C. Gaillard). 0168-583X/00/$ - see front matter Ó 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 9 9 ) 0 0 8 9 4 - 0