Ion Irradiation Effects in Synthetic Garnets Incorporating Actinides
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Ion Irradiation Effects in Synthetic Garnets Incorporating Actinides Satoshi Utsunomiya1, Lu-Min Wang1, Sergey Yudintsev2 and Rodney C. Ewing1,3 1 Department of Nuclear Engineering and Radiological Sciences, 3Department of Geological Sciences, The University of Michigan, Ann Arbor, Michigan 48109-2104, U.S.A. 2 Institute of Geology of Ore Deposits, Russian Academy of Sciences, Staromonetny 35, 109017 Moscow, RUSSIA. ABSTRACT Radiation durability of garnet [A3B2(XO4)3; Ia3d; Z=8] has been examined by 1.0 MeV Kr2+ irradiation with in situ transmission electron microscopy over the temperature range of 50 to 1070 K. The targets were five synthetic garnets incorporating various contents of actinides and andradite, Ca3Fe2Si3O12. The synthetic garnets were silicates (N series) and ferrate-aluminate series (G series). The critical amorphization temperatures (Tc), above which amorphization does not occur, were determined to be 1050 K for N77, 1130 K for N56, 1100 K for G3, 890 K for G4 and 1030 K for andradite. Tc of the synthetic garnets increased as the average atomic mass of the garnet increased. The maximum transferred energy by ballistic interaction was positively correlated to the atomic mass. The larger cascade size that formed due to the larger Emax might lead to the higher Tc. INTRODUCTION Incorporation of actinides into ceramics is an important issue for the immobilization of radionuclides in the high level waste (HLW) form, and the radiation durability of potential host materials for HLW form requires careful consideration [1, 2]. Because the long term radiation effects due to radioactive decay can be simulated in short term with heavy ion-irradiation[3], many irradiation experiments using heavy ions have been completed in the potential ceramics for HLW, which are summarized in [4, 5]. Garnet is one of the candidates for HLW host because it can incorporate actinides, Zr and rare earth elements into its crystal structure. Garnet based ceramics have been synthesized recently for the immobilization of actinide elements [6-8]. Wang et al. [9] first investigated ion-irradiation effects in complex silicates with in situ transmission electron microscopy (TEM). Eby et al. [10] then examined the relationship between physical-chemical properties and the critical amorphization dose of 25 complex silicates at room temperature. Almandine, andradite, grossular and spessartine were included in the Eby et al. study [10]. But the temperature dependence of the critical amorphization dose of the garnet was not investigated in this first study. A few data for pyrope at T < 673 K were measured in a systematic ion irradiation study of phase in the MgO-Al2O3-SiO2 system [11]. Synthetic garnets incorporating rare earth elements (REE) are also important for other industrial applications, particularly yttrium aluminum garnet (YAG), Y3Al5O12 and YAG doped by other ions for use in laser systems and in digital display systems [12]. However the radiation susceptibility of the garnet structure incorporating actinides, REE, etc. to the amorphiza
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