Determination of radon-222 and radium-226 in water samples by Cerenkov counting

Abstract

Cerenkov radiation produced by the high-energy β-particles emitted from ²¹⁴Bi, a daughter of ²²²Rn (and ²²⁶Ra), was utilized for the determination of ²²²Rn and ²²⁶Ra in water samples. For the determination of ²²²Rn the gas is extracted into an organic solvent and counted 2 h after extraction using a liquid scintillation counter. For the determination of ²²⁶Ra a sample storage time of 25 d is necessary to allow secular equilibrium to be established. The effects of extraction procedures, storage conditions and the nature of the organic solvent were evaluated using standard ²²⁶Ra solutions. Toluene was found to be the most suitable solvent, both as an extractant and as a transparent medium for Cerenkov radiation. Minimizing the volume of the air space above the liquid phase and centrifuging the organic solvent after extraction led to a good recovery of radon and a clean extraction, a detection limit of 35.1 mBq l^–1 being achieved. Some results for water samples in the UK are presented.