Measurement of radon-222 and radium-226 in ground water by liquid scintillation counting

A pilot study was carried out to establish the hydrogeological controls on radon and radium concentrations in potable groundwaters from selected aquifer types throughout Australia. The draft AWRC/SHMRC drinking water guidelines specify a recommended value of 100 BqL-1 for Rn-222 and 0.5 BqL-1 for Ra-226 and Ra-228. Preliminary measurements in groundwater indicate enormous variability for Rn-222 concentrations; from 10 BqL-1 in limestone to 500 BqL-1 in granitic and high grade metamorphic fractured rock systems. The associated Ra-226 concentrations are much lower (<0.5 BqL-1). Measurements are carried out using the LKB Wallac Quantulus liquid scintillation counter which has an overall efficiency of >250% for radon and it's short lived α emitting progeny. Background count rates are around 0.7 cpm. Figure of merit (E2/B) values of around 10 000 are obtained using NEN High Efficiency Mineral Oil cocktail to water sample ratios of 2:1. These figures concur with findings in Europe and North America regarding prelevance of high radon concentrations in hard-rock formation. 8 refs., 1 tab., 1 fig