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 gamma-emitting isotope 95mTc (T1/2=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.