Ca-41 Ultratrace Determination With Isotopic Selectivity > 10(12) By Diode-Laser-Based Rims

Ca-41 ultratrace determination by diode-laser-based resonance ionization mass spectrometry with extremely high isotopic selectivity is presented. Application to environmental dosimetry of nuclear reactor components, to cosmochemical investigations of production cross sections, and biomedical isotope-tracer studies of human calcium kinetics are discussed. Future investigations are possible use in Ca-41-radiodating. Depending on the application, Ca-41 isotopic abundances in the range of 10(-9) to 10(-15) relative to the dominant stable isotope Ca-40 must be determined. Either double- or triple-resonance optical excitation with narrow-band extended cavity diode lasers and subsequent non-resonant photoionization of calcium in a collimated atomic beam were used. The resulting photoions are detected with a quadrupole mass spectrometer optimized for background reduction and neighboring mass suppression. Applying the full triple-resonance scheme provides a selectivity of similar to 5 x 10(12) in the suppression of neighboring isotopes and > 10(8) for isobars, together with an overall detection efficiency of similar to 5 x 10(-5). Measurements on a variety of sample types are discussed; the accuracy and reproducibility of the resulting Ca-41/Ca-40 isotope ratios was better than 5%.