Accelerator mass spectrometry of Tc-99

The measurement of low levels of Tc-99 (T-1/2 = 213 ka) by accelerator mass spectrometry (AMS) is reported for the first time. Because there are no st able isotopes of technetium, the Tc-99 content of a sample is determined fr om the ratio of Tc-99 to a known trace amount of Rh-103. High-purity alumin ium oxide constitutes the bulk of each sample. The contribution from the Ru -99 isobar may be quantified and subtracted using Ru-101. In contrast to co nventional AMS in which at least one isotope is measured as a beam current, here all three isotopes, Tc-99, Ru-101 and Rh-103, are counted ion-by-ion in a propane-filled ionization chamber. This ionization chamber permits par tial, but not complete, separation of Tc-99 from Ru-99 ions. The technique has been validated using a series of standards, as well as a set of five se aweed samples from an inter-laboratory comparison exercise. In addition, th e technique has been used to measure the relative intensities of the Tc- an d TcOm- (m = 1-4) negative ions from a Cs sputter ion source. (C) 2000 Else vier Science B.V. All rights reserved.