Rapid Determination of 226/228Ra in Water Samples
Summary of Method
Ra isotopes are separated and measured from 1.0-1.5 liter samples of terrestrial waters. Radium is concentrated from samples on MnO2 Resin. After a >36 hour ingrowth period for 228Ac from 228Ra, radium and 228Ac are separated from matrix ions and potentially interfering radionuclides using stacked 2mL cartridges of Eichrom LN and DGA Resins. 228Ac is prepared for gas flow proportional counting using a cerium fluoride microprecipitation onto Eichrom Resolve® Filters. 226Ra is prepared for alpha spectrometry using a barium sulfate microprecipitation onto Eichrom Resolve® Filters. Chemical yield of radium is determined by adding either a 133Ba or 225Ra(229Th) tracer. A single operator can process batches of 12-24 samples in 4-5 hours. Results for 226Ra and 228Ra can be obtained in 48 hours, including >36 hour ingrowth time for 228Ac. Results for 226Ra and 228Ra in spiked river and ground water samples typically agreed to within 5% of reference values. If tracing 226Ra with 225Ra(229Th) a minimum 8 hour ingrowth time for the 217At daughter of 225Ra is required.