Preparation of Extra-pure Na 2 CO 3 Powder with Crystallization Techniques for Low-Background Scintillation Crystal Grow
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aration of Extra-pure Na2CO3 Powder with Crystallization Techniques for Low-Background Scintillation Crystal Growth I. I. Novoselova, O. V. Gilevab, *, **, J. S. Choeb, K. A. Shinb, V. N. Shlegela, V. D. Grigorievaa, M. H. Leeb, c, Y. D. Kimb, c, and H. K. Parkd aNikolaev
Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia b Center for Underground Physics, Institute for Basic Science (IBS), Daejeon, 34126 Korea cIBS School, University of Science and Technology (UST), Daejeon, 34113 Korea d Department of Accelerator Science, Graduate School, Korea University, Sejong, 30019 Korea *e-mail: [email protected] **e-mail: [email protected] Received October 30, 2019; revised March 3, 2020; accepted March 5, 2020
Abstract—A method for the preparation of extra-pure Na2CO3 powder has been developed. The method is based on a fractional crystallization of Na2CO3 from its saturated solutions and its conversion into sodium formate, followed by a melt crystallization. To obtain the final product Na2CO3, the recrystallized sodium formate was thermally decomposed. The contents of Th and U in the purified powder were below 10 ppt, the concentrations of Mn, Co, Ba, and Pb were not above 3 ppb, the concentrations of Cu and Sr were on the level of tens of ppb, and the K concentration was about 200 ppb. The ICP-MS analysis showed that the purity of the obtained powder significantly surpasses that for commercial products in 99.997 and 99.999% purity grades. The sodium carbonate powder thus obtained is going to be used as initial material for growing scintillation single crystals in experiments searching for the neutrinoless double beta decay (0νββ) or dark matter. Keywords: extra-pure sodium carbonate powder, fractional recrystallization from aqueous solution, melt crystallization by Inclined Rotary Bridgman method, ICP-MS analysis DOI: 10.1134/S0020168520080105
INTRODUCTION The scintillation crystal bolometer is a powerful technology for such a sensitive experiment like the search for neutrinoless double-beta decay (0νββ), which is the only practical way to determine the absolute neutrino mass scale and the nature of the neutrino as a Majorana or Dirac particle [1–4]. One of the crucial points for successful performance in this experiment is the development of a protocol for producing high-quality single-crystal scintillators with an extremely high internal radiopurity, in an ideal case, zero internal radioactive background. The Advanced Mo-based Rare process Experiment (AMoRE) is an international collaboration for an experimental search for the neutrinoless double beta decay of the 100Mo nuclide. The experiment is running in a series of phases, possibly, using several different scintillating crystals: CaMoO4 (CMO), Li2MoO4 (LMO), PbMoO4 (PMO), and Na2Mo2O7 (NMO) [5]. In the framework of the other projects investigating rare decays, some other crystals are also studied, for example, Na2W2O7 (NWO) [6].
The present study will be focused on the purification of sodium carbonate, whi
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