Trace detection of 41Ca in nuclear reactor concrete by diode-laser-based resonance ionization mass spectrometry

The content of the long-lived isotope 41 Ca in concrete samples obtained from the biological shield of a shut-down nuclear research reactor has been determined by diode-laser-based resonance ionization mass spectrometry (RIMS). Standard procedures were applied for the chemical separation of calcium. A radioactive tracer of 47 Ca was used to determine the chemical yield. The total calcium concentration in the final nitric acid solution was measured by x-ray fluorescence (XRF) spectroscopy. The RIMS measurement yielded the abundance of 41 Ca relative to the total calcium content with a detection limit of 5×10 -10 , limited by background effects at mass 41. The detection limit corresponds to a minimum detectable specific 41 Ca activity of ~100 mBq/g in the concrete. Reproducibility and accuracy were determined with 41 Ca spikes and found to be in the range of 15%, limited predominantly by ion counting statistics.