Radium interference during radon measurements in water: comparison of one- and two-phase liquid scintillation counting.

Assessment of radiation exposure to drinking, surface, and groundwater and of the associated health risks calls for accurate and precise ²²⁶Ra and ²²²Rn measurements. One method that fits the bill is liquid scintillation counting (LSC), which allows measurements in one-phase (homogenous) or two-phase samples. The aim of our study was to compare the measurement efficiency with both variations in Niška Banja spa water, known for its elevated ²²²Rn content to get a better insight into the stability and behaviour of the samples and ²²⁶Ra interference in samples spiked with ²²⁶Ra with ²²²Rn measurement. ²²⁶Ra interference was more evident in homogenous, one-phase and much lower in two-phase samples. However, one-phase samples offer more accurate indirect ²²⁶Ra measurements. Water-immiscible cocktails (in two-phase samples) have shown a limited capacity for receiving ²²²Rn generated by Ra decay from the aqueous to organic phase when ²²²Rn/²²⁶Ra equilibrium is reached. We have also learned that samples with naturally high ²²²Rn content should not be spiked with ²²⁶Ra activities higher than the ones found in native samples and that calibration of two-phase samples can be rather challenging if measurements span over longer time. Further research would require much lower ²²⁶Ra activities for spiking to provide more practical answers to questions arising from the demonstrated phenomena.