Effects of Proton Irradiation in Zeolite-Y
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Effects of Proton Irradiation in Zeolite-Y Binxi Gu1, Lumin Wang1, Shixin Wang1, Donggao. Zhao1, Victor H. Rotberg2, and Rodney C. Ewing1 1 Department of Nuclear Engineering and Radiological Sciences, 2Michigan Ion Beam Laboratory University of Michigan, Ann Arbor, MI 48109. ABSTRACT Radiation effects on zeolite-NaY have been investigated by irradiation with a 500 keV H+ beam. The crystalline-to-amorphous transition occurs at a total dose equivalent to an ionizing energy deposition of 3×1010 Gy and a displacement damage level of 0.05 dpa. The ion exchange capacity of the irradiated zeolite-NaY with 10 mN SrCl2 or 10 mN AgNO3 solutions varies with the extent of the damage to the crystalline structure. After 25 hours of exchange, the Sr concentration in the amorphous region is nearly zero. This result shows that radiation-induced amorphization can cause a significant loss in ion exchange capacity. The data also suggest that the radiation damage by proton radiation in zeolite-NaY is through both ionizing and displacement processes. The result from Ag-exchange reaction with the irradiated zeolite suggests that higher radiation dose is required to block the penetration of Ag into the supercages. The Ag concentration (~3 at.%) in the fully damaged region suggests that the cations in the small cages are still exchangeable even when amorphization has been achieved. INTRODUCTION Zeolites are of considerable interest in the nuclear industry because of their variety of applications as waste processing media, waste form and potential back-fill material in nuclear waste repositories. Zeolite-group phases have also been identified as precipitates on the corroded surfaces of nuclear waste glasses [1]. Rare-earths, actinides, Cs, and Sr can be incorporated into the zeolite phase through ion exchange reactions [1,2]. Previous studies have shown that zeolites are extremely susceptible to radiation-induced amorphization. Amorphization can be induced by both radiolysis and collisional displacement mechanisms. Accompanying amorphization, bubbles containing structural water and/or other volatile components may form under intense ionizing irradiation [3,4]. Since radiation may cause significant changes in the physical and chemical properties of zeolites as a result of structural damage, it is important to investigate the changes in the ion exchange and retention capacity of irradiated zeolites. However, only limited research has been completed in this regard. The published results based on conventional “wet” chemical methods of measuring the ion-exchange capacity are generally contradictory due to the difficulties in conducting high dose irradiations [5,6]. In the present study, zeolite-NaY samples were irradiated with energetic protons so that significant damage was produced in a volume large enough for chemical experiments. Instead of analyzing the solution chemistry to determine the changes of chemical properties in the irradiated zeolite, electron microprobe analysis (EMPA), transmission electron microscopy (TEM) and scanning electron
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