Effective Determination of the Long-lived Nuclide ~(41)Ca in Nuclear Reactor Bioshield Concretes: Comparison of Liquid Scintillation Counting and Accelerator Mass Spectrometry

摘要

The routine application of liquid scintillation counting to ~(41)Ca determination has been hindered by the absence of traceable calibration standards of known ~(41)Ca activity concentrations. The introduction of the new IRMM ~(41)Ca mass-spectrometric standards with sufficiently high ~(41)Ca activities for radiometric detection has partly overcome this although accurate measurement of stable Ca concentrations coupled with precise half-life data are still required to correct the certified ~(41)Ca:~(40)Ca ratios to ~(41)Ca activity concentrations. In this study, ~(41)Ca efficiency versus quench curves have been produced using the IRMM standard, and their accuracy validated by comparison with theoretical calculations of ~(41)Ca efficiencies. Further verification of the technique was achieved through the analysis of ~(41)Ca in a reactor bioshield core that had been previously investigated for other radionuclide variations. Calcium-41 activity concentrations of up to 25 Bq/g were detected. Accelerator mass spectrometry (AMS) measurements of the same suite of samples showed a very good agreement, providing validation of the procedure. Calcium-41 activity concentrations declined exponentially with distance from the core of the nuclear reactor and correlated well with the predicted neutron flux.