Rapid method for determination of 228Ra in water samples
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A new rapid method for the determination of 228Ra in natural water samples has been developed at the SRNL/EBL (Savannah River National Lab/Environmental Bioassay Laboratory) that can be used for emergency response or routine samples. While gamma spectrometry can be employed with sufficient detection limits to determine 228Ra in solid samples (via 228Ac), radiochemical methods that employ gas flow proportional counting techniques typically provide lower minimal detectable activity levels for the determination of 228Ra in water samples. Most radiochemical methods for 228Ra collect and purify 228Ra and allow for 228Ac daughter ingrowth for ~36 h. In this new SRNL/EBL approach, 228Ac is collected and purified from the water sample without waiting to eliminate this delay. The sample preparation requires only about 4 h so that 228Ra assay results on water samples can be achieved in <6 h. The method uses a rapid calcium carbonate precipitation enhanced with a small amount of phosphate added to enhance chemical yields (typically >90 %), followed by rapid cation exchange removal of calcium. Lead, bismuth, uranium, thorium and protactinium isotopes are also removed by the cation exchange separation. 228Ac is eluted from the cation resin directly onto a DGA Resin cartridge attached to the bottom of the cation column to purify 228Ac. DGA Resin also removes lead and bismuth isotopes, along with Sr isotopes and 90Y. La is used to determine 228Ac chemical yield via ICP-MS, but 133Ba can also be used instead if ICP-MS assay is not available. Unlike some older methods, no lead or strontium holdback carriers or continual readjustment of sample pH is required.
KeywordsRapid 228Ra 228Ac DGA Resin Natural waters
This work was performed under the auspices of the Department of Energy, DOE Contract No. DE-AC09-96SR18500. The authors wish to acknowledge Staci Britt, Jack Herrington and Becky Chavous for their assistance with this work.
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