Cathodoluminescence study of americium incorporation into calcite single crystals
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Cathodoluminescence study of americium incorporation into calcite single crystals Maria V. Zamoryanskaya, Boris E. Burakov, Ekaterina V. Kolesnikova and Michael A. Zuykov Laboratory of Applied Mineralogy and Radiogeochemistry, V.G. Khlopin Radium Institute, 28, 2-nd Murinskiy ave., St. Petersburg, 194021, Russia ABSTRACT In order to study americium incorporation into calcite, CaCO3, under conditions of crystal growth, two samples of single crystal Am-doped calcite were synthesized and studied by cathodoluminescence (CL) spectroscopy in comparison with undoped and Eu-doped artificial calcite. Americium contents in calcite crystals were (in kBq/g): 1) 6.9; 2) 1.9(E+4). The CL emission of undoped and Am-Eu-doped calcite samples was characterized by three broad bands at 2.03; 2.47 and 2.96 eV. Weak CL lines related to typical transitions 5D0 7F1,2,4 of Eu3+ and Am3+ ions were observed at 1.68; 1.99, 2.06 eV and 1.60; 1.98 eV, respectively. Degrading of calcite structure under irradiation has been studied using CL emission of high power electron beam. INTRODUCTION Americium, 241Am, is a highly radioactive and chemically mobile element of nuclear wastes. There is a lack of information concerning Am fixation i.e. sorption on the surface and incorporation into crystalline structure of natural carbonate minerals such as calcite and aragonite, which are main compounds of mollusk shells and limestone sediments. Soluble carbonate form was reported for Np5+ in Boom Clay water [1] and it might be typical for other actinides under conditions of some geological formations. This means that transport of carbonate complexes of actinides from underground repository will be accompanied by actinide incorporation into the structures of new formed natural carbonate minerals. In order to study Am incorporation into calcite structure two samples of Am-doped calcite were synthesized and studied in comparison with undoped and Eu-doped artificial calcite. The main objective of this research was to summarize principal features of artificial Am-doped calcite. These data and samples will be used as analytical standards to compare with natural carbonate samples including mollusk shells collected in contaminated areas. An additional goal was to study degrading of calcite structure under irradiation and effects of doping impurities using CL emission excited by high power electron beam. EXPERIMENTAL DETAILS Samples of artificial calcite were synthesized at room temperature using well-known P. M. Gruzensky method of calcite single crystal growth [2]. Starting aqueous solution of NH4Cl (23-24 wt.%) and CaCl2 (2 wt.%) was placed into open glass or plastic bottles in amount of 2 liters per bottle. In order to provide Am and Eu doping the Am-or Eu-chlorides were added. As a source of CO2, the powder of (NH4)2CO3 was placed into open plastic box located above the bottles with starting solutions. Undoped and Am-Eu-doped calcite crystals 1-3 mm in size were obtained on the walls of plastic bottles after 3 weeks (Fig.1). All crystals obtained were transparent
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