Calibration of the direct LSC method for radon in drinking water: Interference from (210)Pb and its progenies accumulated in (226)Ra standard solution.

The standard ASTM method is the most commonly applied method for determining (222)Rn in drinking water. The method is calibrated with a (226)Ra standard solution that usually contains variable amounts of (210)Pb, (210)Bi and (210)Po if the standard has not recently been purified. Until now it has not been experimentally confirmed that these progenies do not interfere when the method is calibrated. In this study, interference was examined using three different organic cocktails and alpha/beta liquid scintillation spectrometry to separately assess the effect of three radionuclides. The interference from (210) Po was 4% for one of the cocktails if the (226)Ra standard had been purified 5 years earlier. The interferences from (210)Pb and (210)Bi were negligible compared to that of (210)Po.