Simultaneous determination of 226Ra and 210Pb in groundwater and soil samples by using the liquid scintillation counter – suspension gel method

Abstract

A method for the simultaneous determination of 226Ra and 210Pb in groundwater and soil samples by liquid scintillation counting was developed. Radium and lead were separated together from the samples as Ba(Ra)·PbSO 4 co-precipitate, which was centrifuged and dissolved with 0.1 M EDTA solution (pH 9.0). Radium was separated as Ba(Ra)SO 4 co-precipitate by adding ammonium sulfate and adjusting the pH of the solution to 4.2. Lead remaining in the solution was separated as PbSO 4 precipitate by adding 9 M sulfuric acid. These Ba(Ra)SO 4 and PbSO 4 precipitates were purified with EDTA solution and used for measurement. To save time and to make counting samples simpler, direct counting of Ba(Ra)SO 4 and PbSO 4 precipitates instead of the phosphoric acid fusion method was attempted. Ba(Ra)SO 4 and PbSO 4 precipitates were suspended in the scintillation gel, and measured. Two liquid scintillation cocktails, Instagel ® XF and UltimaGold™ AB were used to prepare the counting samples. A mixture of water (40%), Instagel® XF (40%) and UltimaGold™ AB (20%) formed a stable gel. Activities of 226Ra and 210Pb were calculated from the alpha spectrum of Ba(Ra)SO 4 and beta spectrum of PbSO 4, respectively. The long-term stability of the suspension gel was good. The analytical results of 226Ra and 210Pb in spiked groundwater samples were in good agreement with the known concentrations of 226Ra and 210Pb. The analytical values of 226Ra and 210Pb in the soil reference samples were within 11.5 and 1.6% of the relative error from the reference values, respectively.