Automated radioanalytical system for the determination of 90Sr in environmental water samples by 90Y Cherenkov radiation counting.
Strontium-90 is an environmental contaminant at several U.S. Department of Energy sites, including the Hanford site, Washington. Due to its high biological toxicity and moderately long half-life of approximately 29 years, groundwater and surface water contamination plumes containing 90Sr must be closely monitored. The highly energetic beta radiation from the short-lived 90Y daughter of 90Sr generates Cherenkov photons in aqueous media that can be detected by photomultiplier tubes with good sensitivity, without the use of scintillation cocktails. A laboratory-based automated fluid handling system coupled to a Cherenkov radiation detector for measuring 90Sr via the high-energy beta decay of its daughter, 90Y, has been assembled and tested using standards prepared in Hanford groundwater. A SuperLig 620 column in the system enables preconcentration and separation of 90Sr from matrix and radiological interferences and, by removing the 90Y present in the sample, creates a pure 90Sr source from which subsequent 90Y ingrowth can be measured. This 90Y is fluidically transferred from the column to the Cherenkov detection flow cell for quantification and calculation of the original 90Sr concentration. Preconcentrating 0.35 L sample volumes by this approach, we have demonstrated a detection limit of 0.057 Bq/L using a 5 mL volume Cherenkov flow cell, which is below the drinking water limit of 0.30 Bq/L. This method does not require that the sample be at secular equilibrium prior to measurement. The system can also deliver water samples directly to the counting cell for analysis without preconcentration or separation, assuming that the sample is in secular equilibrium, with a detection limit of 7 Bq/L. The performance of the analysis method using a preconcentrating separation column is characterized in detail and compared with direct counting. This method is proposed as the basis for an automated fluidic monitor for 90Sr for unattended at-site operation.
O'Hara
Matthew J
MJ
Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA. Matthew.OHara@pnl.gov
Burge
Scott R
SR
Grate
Jay W
JW
D001331:Automation; D008962:Models, Theoretical; D011834:Radiation Monitoring / Q000379:methods*; D011874:Radiometry; D013326:Strontium Radioisotopes / Q000032:analysis*; D014875:Water Pollutants, Radioactive / Q000032:analysis*; D015021:Yttrium Radioisotopes / Q000032:analysis*
D013326:Strontium Radioisotopes; D014875:Water Pollutants, Radioactive; D015021:Yttrium Radioisotopes