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

The content of the long-lived isotope Ca-41 in concrete samples obtained from the biological shield of a shutdown nuclear research reactor has been determined by diodelaser-based resonance ionization mass spectrometry (RIMS). Standard procedures were applied for the chemical separation of calcium. A radioactive tracer of Ca-47 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 41Ca relative to the total calcium content with a detection limit of 5x10(-10), Limited by background effects at mass 41. The detection limit corresponds to a minimum detectable specific Ca-41 activity of similar to 100 mBq/g in the concrete. Reproducibility and accuracy were determined with Ca-41 spikes and found to be in the range of 15 %, limited predominantly by ion counting statistics.