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.