Determination of ⁴¹Ca with LSC and AMS: method development, modifications and applications

The isotope ⁴¹Ca is produced by neutron capture of the stable and most abundant calcium nuclide ⁴⁰Ca in concrete of the bioshield around nuclear reactors. Because of its long half-life (1.04*10⁵ a) the declaration of ⁴¹Ca in concrete is often requested for radioactive waste disposal.
The radioanalytical ⁴¹Ca determination by liquid scintillation counting (LSC) is still a reasonable option for laboratories involved in decommissioning of nuclear installations despite the emission of only low-energy Auger electrons (ca. 3.6 keV) and the difficulty of obtaining a certificated standard. Besides accelerator mass spectrometry (AMS), being the most sensitive analytical technique not only for ⁴¹Ca, is increasingly gaining broader accessibility and applicability. Herein, we present a radiochemical separation procedure developed for ⁴¹Ca determination with LSC and AMS in varying materials. The radioanalytical isolation consists of anion exchange and extraction chromatography as well as carbonate precipitation and recrystallization from organic solvents. Thereby, disturbing radionuclides as ⁵⁵Fe, ⁶⁰Co, ⁹⁰Sr, ¹³⁷Cs, ¹⁵²Eu or ²⁴¹Pu are removed with decontamination factors of 10²-10⁴. Quench curves for determining the measurement efficiency are generated with a ⁴¹Ca solution gained from the ⁴¹Ca/⁴⁰Ca certified reference material ERM-AE701. In routine application the procedure is characterized by chemical yields of 25-80%, measurement efficiencies of 1-10% and detection limits of 0.05 Bq*g^-1 ash and 0.3 Bq*l^.1. Aliquot solutions of LSC can be easily converted into CaF₂-AMS-targets by successive oxalate and fluoride precipitation. Pros and cons for both measurement techniques are addressed based on ⁴¹Ca results from LSC and AMS for the same material.