Cathodoluminescence of Ce, U and Pu in a Garnet Host Phase
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ABSTRACT Ceramic materials based on garnet, (Y,Gd,An,. . .)3(Al,Ga,An,. . .)5012 and perovskite (Y,Gd,An,..)(AI,Ga,An,. . .)03 structures have been proposed for the immobilization of weaponsgrade actinide-containing waste materials with complex chemical compositions. Cathodoluminescence (CL) images and emission spectra of synthetic garnet and perovskite crystals containing Ce, U and Pu were studied. It was determined that Pu3+ incorporated into the garnet matrix has characteristic CL emission bands at 1.9 and 1.6 eV. The loading capacity of the garnet lattice for Pu 4 + incorporation is significantly higher than for Pu 3+ and similar to U 4+. The maximum amount of Pu3+ that may be incorporated into the garnet structure experimentally is 0.3 wt.% in comparison with 5.3 wt.% for Pu 4+. The CL emission spectra of Ce3+ in different materials is a characteristic property and can be used for identification of garnet and perovskite phases into the multiphase ceramic matrices simultaneously with microprobe analysis. INTRODUCTION Ceramics based on garnet, (Y,Gd,An,. ..)3(AI,Ga,An,.. .)5012 and perovskite (Y,Gd,An,..)(AI,Ga,An,. . .)O3 have been proposed for the immobilization of weapons-grade actinide-containing wastes of complex chemical compositions. Crystalline phases such as garnet and perovskite are chemically and phisically extremely durable and thus desirable for the incorporation of Pu, Am, and other actinide and non-radioactive elements found in waste streams [ 1-3]. The lattice capacity of these materials, however, depends on the valence state and the ionic radius of the substituted ions [3]. Previous work has demonstrated that cathodoluminescence (CL) allows the determination of the following ions from the characteristic CL emission of those elements in different materials: Ce 3÷, U6÷ Cr3+, Gd3 + [3]. The main features of the CL emission of ions depends on the crystalline structure of the host phase and the ion(s) emitting the CL. In some cases, CL may be also used for phase identification. The main goal of this work was to study the Pu valence state in Pu-activated garnet using CL. No information was found in the literature concerning CL emission of the Pu-ion into the crystalline matrices. An additional purpose was to use CL for phase identification of Ce and Pu-doped gamet/perovskite ceramic materials.
EXPERIMENTAL METHODS Powdered starting materials of different stoichiometry consisting of Gd, Al, Ca, Pu, Ce, Ga, Snoxides were been cold pressed in order to obtain pellets 5 mm in diameter. The pellets were then melted in air using a hydrogen torch for 5-8 minutes. The temperature of the hydrogen torch was not measured precisely but was estimated to be approximately 1900-2100'C. In comparison to the flame melting temperatures for all samples were approximately 300-400'C less. One sample 437 Mat. Res. Soc. Symp. Proc. Vol. 608 © 2000 Materials Research Society
of pure monocrystalline Y3A150l 2 (YAG) was cut by using a diamond blade to obtain a sample with dimensions of 2 x 2 x 25 mm. Then, PuO 2 powder was sp
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