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

Abstract

The Radium Delayed Coincidence Counter (RaDeCC) is one of the most extensively used equipment for measuring 223 Ra and 224 Ra 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 223 Ra and 224 Ra. 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 223 Ra and 224 Ra 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 223 Ra and 224 Ra activities (up to~40% and 30%, respectively), as well as the quantification of their parents 227 Ac and 228 Th. High activities of 226 Ra may also produce an overestimation of 224 Ra activities due to the buildup of 222 Rn, especially when long measurements with low activities of 224 Ra are performed. An improved method to quantify 226 Ra activities from the buildup of 222 Rn with the RaDeCC system is also developed in this study.Wethus provide a new set of guidelines for the appropriate quantification of 223 Ra, 224 Ra, 227 Ac, 228 Th, and 226 Ra 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 questions in a study that contains a comprehensive analysis of the RaDeCC counting mechanism and the determination of the limits of quantification. This study should serve as guidance for the measurement and quantification of Radium isotopes for the scientific community using the RaDeCC system. Key Points: • The maximum quantification limits for 223 Ra and 224 Ra are 200 and 100 cpm in the total channel, respectively • Limits for the quantification of 223 Ra and 224 Ra are provided when measurements are influenced by cross-talk and 222 Rn buildup...

Nutrient fluxes from rivers, groundwater, and the ocean into the coastal embayment along the Sanriku ria coast, Japan

“…In this study, 223 Ra and 224 Ra represent the excess activities of 223 Ra and 224 Ra, respectively. In the estimates of saline SGD flux, we used 224 Ra in Ra mass balance model because 223 Ra activity might have larger analytical uncertainty (Diego‐Feliu et al 2020). After a sufficient amount of time (> 1 yr) had elapsed to produce 228 Th distinguishable from 228 Ra decay, we measured 228 Th and estimated the initial 228 Ra activity ( 228 Ra i ) according to the following equation (Moore 2008): where 228 Ra i and 228 Th i are the initial activities of 228 Ra and 228 Th, respectively, in the sample, 228 Th m is the measured 228 Th activity after t days, and λ Ra and λ Th are the decay constants of 228 Ra (0.99 × 10 −3 d −1 ) and 228 Th (0.33 × 10 −3 d −1 ), respectively.…”

Submarine karstic springs as a source of nutrients and bioactive trace metals for the oligotrophic Northwest Mediterranean Sea

“…The Mnfibers were triple rinsed with Ra-free deionized water and partially-dried using compressed-air until a fiber-to-water ratio of 1:1 was achieved (Sun and Torgersen, 1998). The short-lived 223 Ra and 224 Ra isotopes were counted using a delayed coincidence counter (RaDeCC) (Moore and Arnold, 1996) following the counting recommendations described in Diego-Feliu et al (2020). In the case of high activity samples, a second count was performed between 7…”

RaDeCC Reader: Fast, accurate and automated data processing for Radium Delayed Coincidence Counting systems

“…The 1 st interval read, performed as soon after sampling as possible, is a measurement of radium-223 and radium-224 activity, this will be a combination of excess and supported activities. A 2 nd interval, 7-10 days after sampling, can provide a more accurate radium-223 activity due to reduced interference from radium-224 and radon-220 decay (Moore, 2008), and is essential in instances where the 220/219 count rate is greater than 10, or greater than 4 and the 220 channel exceeds 5 cpm (Diego Feliu et al 2020). Eventually, >99% of measured radium-224 and radium-223 activities will be supported by their parent isotopes.…”

“…Volume-corrected radium-226 activity of the sample (vdpm226, in dpm/m 3 ) is then calculated using equation 20, where 'vdpm226initial' is the initial volume corrected radium-226 activity (in cpm/m 3 ; equation 19) and 'E226' is the efficiency of system in determining radium-226 activity. This method was devised by Geibert et al, (2013) and modified by Diego-Feliu et al, (2020).…”