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

The standard ASTM method is the most commonly applied method for determining 222Rn in drinking water. The method is calibrated with a 226Ra standard solution that usually contains variable amounts of 210Pb, 210Bi and 210Po 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 α/β 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 226Ra standard had been purified 5 years earlier. The interferences from 210Pb and 210Bi were negligible compared to that of 210Po.