Progress in 41Ca ultratrace determination by diode-laser-based RIMS

We report on progress in development and application of 41Ca ultratrace determination by diode-laser-based RIMS. Applications include biomedical isotope-tracer studies of human calcium kinetics, cosmochemical investigations of meteorites, environmental dosimetry and radiodating. Depending on the application, 41Ca needs to be determined at isotopic abundance in the range of 10−9 to 10−15 relative to the major stable isotope 40Ca. We use either a double- or triple-resonance excitation scheme and subsequent non-resonant photoionization of calcium atoms in a collimated atomic beam. All resonant steps are excited with narrow bandwidth extended cavity diode lasers, non-resonant photo-ionization is attained with either an argon ion laser or a CO2 laser. The resulting photo-ions are detected with a quadrupole mass spectrometer. With double-resonance excitation, the optical isotopic selectivity for 41Ca against 40Ca is 2×104, while the triple-resonance scheme provides optical selectivity of more than 109. By addin...