Accelerator mass spectrometry of ⁹⁹Tc

The measurement of low levels of ⁹⁹Tc (T _1/2 = 213 ka) by accelerator mass spectrometry (AMS) is reported for the first time. Because there are no stable isotopes of technetium, the ⁹⁹Tc content of a sample is determined from the ratio of ⁹⁹Tc to a known trace amount of ¹⁰³Rh. High-purity aluminium oxide constitutes the bulk of each sample. The contribution from the ⁹⁹Ru isobar may be quantified and subtracted using ¹⁰¹Ru. In contrast to conventional AMS in which at least one isotope is measured as a beam current, here all three isotopes, ⁹⁹Tc, ¹⁰¹Ru and ¹⁰³Rh, are counted ion-by-ion in a propane-filled ionization chamber. This ionization chamber permits partial, but not complete, separation of ⁹⁹Tc from ⁹⁹Ru ions. The technique has been validated using a series of standards, as well as a set of five seaweed samples from an inter-laboratory comparison exercise. In addition, the technique has been used to measure the relative intensities of the Tc^- and TcO_m^- (m = 1-4) negative ions from a Cs sputter ion source.