Optimization of parameters for the measurement of radon-222 in water using two phase liquid scintillation counting

The liquid scintillation counting (LSC) technique is one of the most popular and sensitive ways to quantify ²²²Rn in drinking water as it allows automatic analysis of multiple samples. For the accurate and precise determination of ²²²Rn in water samples the calibration procedure was standardized for two-phase systems using Hidex 300 SL. This method implies mixing of water samples with lipophilic scintillation cocktail, which has a high solubility for ²²²Rn, while the more hydrophilic radionuclide like ²²⁶Ra will remain in the aqueous phase and do not interfere with or have a quenching effect on the counting. The efficiency calibrations were found to be more accurate with ²²⁶Ra standard rather than conventionally employed pure alpha and beta standards. The adjustment of the counting window and alpha/beta settings was done by changing the Pulse Length Index (PLI) value iteratively until the alpha and beta regions were separated. Based on the obtained results, with proper adjustment of calibration parameters, the method can be used for determining radon in water. In the developed method, a counting time of 300s was sufficient to obtain a minimum detectable activity below the EPA's²²²Rn limits.