Electrolytic enrichment method for tritium determination in the Arctic Ocean using liquid scintillation counter
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Electrolytic enrichment method for tritium determination in the Arctic Ocean using liquid scintillation counter Feng Lin1*, Tao Yu1, Wen Yu1, Jialin Ni1, Li Lin2 1 Laboratory of Marine Isotopic Technology and Environmental Risk Assessment, Third Institute of Oceanography,
Ministry of Natural Resources, Xiamen 361005, China 2 Laboratory of Marine Biology and Ecology, Third Institute of Oceanography, Ministry of Natural Resources, Xiamen
361005, China Received 30 June 2019; accepted 22 February 2020 © Chinese Society for Oceanography and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract
A method of measuring the tritium in seawater based on electrolytic enrichment and ultra-low background liquid scintillation counting techniques was established. The different factors influencing the detection limit were studied, including the counting time, the electrolytic volume of the seawater samples, the selection of background water, scintillation solution and their ratio. After optimizing the parameters and electrolyzing 350 mL volume of samples, the detection limit of the method was as low as 0.10 Bq/L. In order to test the optimization of system for this method, of the 84 seawater samples collected from the Arctic Ocean we measured, 92% were above the detection limit (the activity of this samples ranged from 0.10 Bq/L to 1.44 Bq/L with an average of (0.30±0.24) Bq/L). In future research, if we need to accurately measure the tritium activity in samples, the volume of the electrolytic samples will be increased to further reduce the minimum detectable activity. Key words: tritium, liquid scintillation, cocktails, electrolytic enrichment Citation: Lin Feng, Yu Tao, Yu Wen, Ni Jialin, Lin Li. 2020. Electrolytic enrichment method for tritium determination in the Arctic Ocean using liquid scintillation counter. Acta Oceanologica Sinica, 39(9): 73–77, doi: 10.1007/s13131-020-1647-4
1 Introduction Tritium (3H) is a radioactive isotope of hydrogen with a halflife of 12.3 years (Gröning and Rozanski, 2003), which emits lowenergy beta particles with a maximum energy of 18.6 keV (Carsten, 1979). It is a naturally occurring radionuclide through the interaction of high-energy cosmic rays with oxygen and nitrogen atoms in the upper atmosphere (Popoaca et al., 2014). The environmental levels of tritium increased after nuclear weapon tests between 1945 and 1963 (Jacobs, 1968; Hua and Wen, 2008), and after that it is mainly released from nuclear facilities, especially the heavy water reactor (HWR) (Jacobs, 1968; Carsten, 1979). Dramatic changes have been observed in the hydrological cycle in the Arctic over the last century, such as changes in the magnitude and timing of ice melting, precipitation and surrounding river discharge, and sea level changes in the Arctic Ocean (Peterson et al., 2002; Aagaard and Carmack, 1989; Carmack, 2000; Serreze et al., 2006). Multiple tracers (e.g., δ18O, δ2H and 3H) have been widely used to identify and quantify the freshwater contribution in studies of water mass compositions and movemen
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