Guidelines and Limits for the Quantification of Ra Isotopes and Related Radionuclides With the Radium Delayed Coincidence Counter (RaDeCC)

• Published in: Journal of geophysical research. Oceans 2020-04, Vol.125 (4), p.n/a
• Main Authors: Diego‐Feliu, M., Rodellas, V., Alorda‐Kleinglass, A., Tamborski, J., Beek, P., Heins, L., Bruach, J. M., Arnold, R., Garcia‐Orellana, J.
• Format: Article
• Language: English
• Subjects: Alpha decay; Coincidence circuits; Corrections; Decay; Environmental Sciences; Geophysics; Groundwater; Groundwater discharge; Guidelines; Hydrology; Isotopes; Measurement; Measurement methods; Measuring instruments; Oceanographers; quantification; Ra isotopes; RaDeCC; Radioisotopes; Radionuclide kinetics; Radium; Radium 226; Radium isotopes; Radium radioisotopes; Radon; Radon isotopes; Ratios; Sediment samplers; Sediment samples; submarine groundwater discharge; U/Th series; Water circulation
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1029/2019JC015544

The Radium Delayed Coincidence Counter (RaDeCC) is one of the most extensively used equipment for measuring 223Ra and 224Ra activities in water and sediment samples. Samples are placed in a closed He‐circulation system that carries the Rn produced by the decay of Ra to a scintillation cell. Each alpha decay recorded in the cell is routed to an electronic delayed coincidence system which enables the discrimination of 223Ra and 224Ra. In this study, the measurement and quantification methods using the RaDeCC system are assessed through analyses of registered data in different RaDeCC systems worldwide and a set of simulations. Results of this work indicate that the equations used to correct for 223Ra and 224Ra cross‐talk interferences are only valid for a given range of activities and ratios between isotopes. Above certain limits that are specified in this study, these corrections may significantly overestimate the quantification of 223Ra and 224Ra activities (up to ~40% and 30%, respectively), as well as the quantification of their parents 227Ac and 228Th. High activities of 226Ra may also produce an overestimation of 224Ra activities due to the buildup of 222Rn, especially when long measurements with low activities of 224Ra are performed. An improved method to quantify 226Ra activities from the buildup of 222Rn with the RaDeCC system is also developed in this study. Wethus provide a new set of guidelines for the appropriate quantification of 223Ra, 224Ra, 227Ac, 228Th, and 226Ra with the RaDeCC system. Plain Language Summary In the last decades, there has been a growing interest in using radioactive isotopes to evaluate environmental processes. Their concentrations in environmental settings can reveal information about provenance, path, time, and duration. In this scenario, the research in the techniques to measure isotopes from samples has played a key role. In 1996, the launching of the Radium Delayed Coincidence Counter (RaDeCC) facilitated the fast and precise measurement of Ra isotopes, which provide information on land‐ocean interaction processes (e.g., groundwater discharge to the sea and coastal residence times). Nowadays, this detector has become a fundamental tool for oceanographers, geochemist, and hydrologist among other scientific communities. Nevertheless, when the RaDeCC system was released, its quantification limits were not provided, and the recommendations on its use were mostly qualitative. More than 20 years later, we address these quest