SAMOP 2021 – scientific programme

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MS: Fachverband Massenspektrometrie

MS 7: Accelerator Mass Spectrometry I

MS 7.5: Talk

Thursday, September 23, 2021, 12:00–12:15, H3

Developments towards the detection of ¹³⁵Cs and ¹³⁷Cs by AMS — •Alexander Wieser¹, Johannes Lachner^1,2, Dorian Zok³, Martin Martschini¹, Peter Steier¹, Alfred Priller¹, and Robin Golser¹ — ¹University of Vienna, Faculty of Physics - Isotope Physics, Vienna, Austria — ²Helmholtz-Zentrum Dresden-Rossendorf, Accelerator Mass Spectrometry and Isotope Research, Dresden, Germany — ³Leibniz Universität Hannover, Institute of Radioecology and Radiation Protection, Hannover, Germany

The isotopic ratio ¹³⁵Cs/¹³⁷Cs can be used to assign sources of anthropogenic cesium input, or as a geochemical tracer, or for modifying anthropogenic radionuclide dispersion models. Due to the long half-life of ≈ 2.3 Ma, ¹³⁵Cs is hard to detect via radiometric methods, while mass spectrometry has to deal with isobaric interferences, i.e. ¹³⁵Ba and ¹³⁷Ba for Cs detection. The new method of Ion Laser InterAction Mass Spectrometry (ILIAMS) at the Vienna Environmental Research Accelerator (VERA) overcomes this problem by exploiting differences in the electron affinities of CsF₂⁻ and BaF₂⁻. A ¹³³CsF₂⁻ current on the order of 50 nA from a mixed Cs₂SO₄ and PbF₂ - matrix is extracted from the ion source. At VERA two sputtering processes are currently investigated: Rubidium sputtering and negative ion production without external sputter agent. First results show reproducible detection of ¹³⁵Cs and ¹³⁷Cs in an in-house reference material, while reaching blank levels of ^135,137Cs/¹³³Cs = 6·10⁻¹². We aim to reduce this value by at least two orders of magnitude for measuring environmental samples.