An efficient and simple method for measuring 226Ra using the scintillation cell in a delayed coincidence counting system (RaDeCC)

A delayed coincidence counter (RaDeCC), developed to determine ultra-low levels of 223Ra (half life = 11.1 days) and 224Ra (half life = 3.6 days) in seawater, was adapted to measure 226Ra (half life = 1622 years). After pre-concentration of Ra from seawater onto MnO2-coated fiber we show in this study that the 226Ra activity can be determined using the RaDeCCʹs ability to record alpha decay of its daughters as total counts. For sufficient ingrowth of 222Rn, the Mn-fiber is hermetically sealed in a column for a few days. Then, the ingrown 222Rn is circulated through the RaDeCC air-loop system followed by shutting down of the pump and closure of the scintillation cell for equilibration. Counting may be completed within a few hours for seawater samples. Sample measurements with this method agreed well with data obtained using gamma-ray spectrometry. This proves that a set of Ra isotopes (223Ra, 224Ra, and 226Ra), commonly used for geophysical studies such as mixing rates of different water masses and submarine groundwater discharge, can be efficiently and rapidly measured using the RaDeCC.