Low level determination of 226Ra in water using a micro-precipitate track method for large-scale environmental monitoring

In the present paper a method has been developed for the determination of 226Ra in water by the detection, using a solid-state nuclear track detector (SSNTD), of alpha particles from 226Ra in equilibrium with 222Rn in micro-precipitates collected on a filter. The micro-precipitates were prepared from environmental water samples by collection of radium with lead as Pb/RaSO4. Several factors affect the 226Ra precipitation on the filter and its recovery, in particular the filter pore size. Therefore in this experiment Whatman no. 42 and Millipore filters with different pore sizes were used. Using a 0.45 μm Millipore filter, the recovery efficiency was increased up to 96%, and the alpha self-absorption and scattering decreased remarkably. For efficient detection of alphas from 226Ra/222Rn in equilibrium, three types of SSNTD were used-polycarbonate (PC) electrochemically etched (ECE), CR-39 and LR-115 chemically etched (CE). By preparing a standard micro-precipitate on a filter with known 226Ra/222Rn characteristics, the calibration response of each detector and its minimum detection limit (MDL) were determined.