Ultratrace determination of 99Tc in the seawater by low energy AMS
Mrs Mosammat Khan, Barbara Francisco, Xiaolei Zhao, Liam Kieser, Ian Clark
The ultrarace determination of 99Tc by AMS is challenging due to the presence of the 99Ru isobar and lack of a stable Tc isotope for ratio measurement. An effective sample preparation method and carefully prepared targets offer an opportunity to achieve low detection limit for the measurement of 99Tc by 3MV-AMS system with the sufficient reduction of 99Ru. In this study, a chemistry methodology was developed to produce 99TcF5– with sufficient suppression of 99Ru5– to allow correction with 101Ru such that measurements down to femtogram (fg) levels of 99Tc are possible. An ICP-MS approach using a prepared standards over a range of 99Tc concentrations has been followed to allow 99Tc-AMS measurement without a stable Technetium isotope. Depending on the sample preparation, a linear correlation of 99Tc concentration has been obtained by improving the sample preparation chemistry to produce the FeOxHy precipitate carrying the 99Tc. Using targets made up of (99Tc)FeOxHy mixed with FeF3, which we find to produce a more stable current than the traditionally used PbF2. The 99Ru background was significantly reduced to ⁓1 fg with the lower detection limit of 99Tc, < 1 fg in the unit of “fg 99Tc per mg of FeOxHy precipitate” using +2 ions in the ionization chamber. This method is anticipated to allow the analysis of 99Tc in environmental samples such as seawater/groundwater and soil.
I, Mosammat Samsunnahar Khan, am a PhD candidate in the department of Earth and Environmental Sciences at the University of Ottawa, Canada. My research topic is “Analytical method development for the separation of long-lived fission products (93-Zr, 99-Tc) from the interfering elements/isobars and measure them in the environment by mass spectrometry.”