Investigating the potential of tandem inductively coupled plasma mass spectrometry (ICP-MS/MS) for 41Ca determination in concrete

Abstract

Concrete is a common structural material used in nuclear reactors for biological shielding, containment buildings, and waste storage ponds. Calcium is a significant component of concrete, with neutron activation of stable ⁴⁰Ca (96.94% abundance) leading to the production of ⁴¹Ca (half-life 1.002(17) × 10⁵ years). The long half-life combined with the significant amount of concrete at nuclear facilities makes ⁴¹Ca a key radionuclide for characterisation of low and intermediate level waste, as well as for long-term waste monitoring. Measurement of ⁴¹Ca by inductively coupled plasma mass spectrometry (ICP-MS) is theoretically achievable, but has previously been prevented by multiple interferences, some of which cannot be removed by offline chemical separation. This study tests the potential of tandem ICP-MS/MS and its enhanced interference separation for the detection of ⁴¹Ca in concrete samples. The instrument setup was initially optimised using stable element standards, with a combination of NH₃, H₂ and He proving to be most effective, achieving an instrument detection limit of 0.32 Bq g⁻¹ (0.099 ng g⁻¹). The procedure was validated on several concrete samples, which required the optimisation of automated borate fusion sample digestion and four-stage chemical separation, with recoveries of 73–77%. Successful detection of ⁴¹Ca was achieved at activity concentrations down to 0.67 Bq g⁻¹ (0.21 ng g⁻¹) at ⁴¹Ca/⁴⁰Ca ratios of 10⁻⁶–10⁻⁷. This represents the first known measurement of ⁴¹Ca using ICP-MS, and recommendations are made on how instrument capabilities can be further improved so that routine measurement can be realised.