Rapid method for 226Ra and 228Ra analysis in water samples

Abstract

The measurement of radium isotopes in natural waters is important for oceanographic studies and for public health reasons. Radium-226 (T1/2 = 1620 y) is one of the most toxic of the long-lived alpha-emitters present in the environment due to its long life and its tendency to concentrate in bones, which increases the internal radiation dose of individuals. The analysis of 226Ra and 228Ra in natural waters can be tedious and time-consuming. Different sample preparation methods are often required to prepare 226Ra and 228Ra for separate analyses. A rapid method has been developed at the Savannah River Environmental Laboratory that effectively separates both 226Ra and 228Ra (via 228Ac) for assay. This method uses MnO2 Resin from Eichrom Technologies (Darien, IL, USA) to preconcentrate 226Ra and 228Ra rapidly from water samples, along with 133Ba tracer. DGA ResinO (Eichrom) and Ln-ResinO (Eichrom) are employed in tandem to prepare 226Ra for assay by alpha-spectrometry and to determine 228Ra via the measurement of 228Ac by gas proportional counting. After preconcentration, the manganese dioxide is dissolved from the resin and passed through stacked Ln-Resin-DGA Resin cartridges that remove uranium and thorium interferences and retain 228Ac on DGA Resin. The eluate that passed through this column is evaporated, redissolved in a lower acidity and passed through Ln-Resin again to further remove interferences before performing a barium sulfate microprecipitation. The 228Ac is stripped from the resin, collected using cerium fluoride microprecipitation and counted by gas proportional counting. By using vacuum box cartridge technology with rapid flow rates, sample preparation time is minimized.