Developments in AMS of ⁹⁹Tc

Sample preparation and AMS methodology for ⁹⁹Tc have been refined with the aim of improving sensitivity to permit measurements on as little as 0.25 l of seawater. Sample preparation improvements have been directed towards minimizing ⁹⁹Ru and maximizing the yield of the ⁹⁹TcO^- ion from the ion source. A range of chemical extraction techniques and the purity of various reagents have been explored. In order to monitor the chemical yield, the γ-emitting isotope ^95mTc (T_1/2=61 days), produced by the ⁹⁵Mo(p,n) ⁹⁵Tc reaction on a natural Mo foil, was added as a tracer. On the AMS side, a new gas-filled ionization detector has been developed. This differs from that used previously in having an anode plane optimised for ⁹⁹Tc, which makes eight measurements of the energy loss along the ion track. A new algorithm for maximizing the separation of ⁹⁹Tc and ⁹⁹Ru from the resulting multiparameter data has been developed, and allows rejection of >90% of the ⁹⁹Ru ions while retaining >90% of the ⁹⁹Tc counts.