Ultra-trace Detection of 99Tc in Environmental Samples by Accelerator Mass Spectrometry

In our project we are developing methods for the detection of the anthropogenic radionuclide 99-Technetium by Accelerator Mass Spectrometry (AMS). For environmental samples, a highly effective chemical sample preparation method was developed, that removes a large fraction of the interfering elements Ruthenium and Molybdenum and embeds the Tc in a Niobium matrix. The samples were measured at the AMS setup of the Maier-Leibnitz-Laboratory in Munich by extraction of 99TcO− from the ion source, stripping to 99Tc12+ and normalizing to the 93Nb11+ current. A particle energy of 150 MeV in combination with the detection via a Time-of-Flight path and the Gas-filled Analyzing Magnet System (GAMS) allows for a sensitivity of 5·1E6 atoms per sample. The method is discussed together with results from environmental samples. In particular, 99Tc concentrations along a water column from the Pacific Ocean, as well as in porewater from an Austrian peat-bog are presented.