36Cl exposure dating with a 3-MV tandem |
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Authors: | Peter Steier Oliver Forstner Robin Golser Walter Kutschera Martin Martschini Silke Merchel Tobias Orlowski Alfred Priller Christof Vockenhuber Anton Wallner |
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Affiliation: | 1. VERA Laboratory, Fakultät für Physik – Isotopenforschung, Universität Wien, Währinger Straße 17, A-1090 Wien, Austria;2. CEREGE, CNRS-IRD-Université Aix-Marseille, Europôle Méditerranéen de L’Arbois, 13545 Aix-en-Provence, France;3. Forschungszentrum Dresden-Rossendorf, D-01314 Dresden, Germany;4. HPK H 31, Institut für Teilchenphysik, ETH Zürich, Schafmattstr. 20 CH-8093 Zürich, Switzerland |
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Abstract: | 36Cl AMS measurements at natural isotopic concentrations have yet been performed only at tandem accelerators with 5 MV terminal voltage or beyond. We have developed a method to detect 36Cl at natural terrestrial isotopic concentrations with a 3-MV system, operated above specifications at 3.5 MV.An effective separation was obtained with an optimized split-anode ionization chamber design (adopted from the ETH/PSI Zurich AMS group), providing a suppression factor of up to 30,000 for the interfering isobar 36S. Despite the good separation, a relatively high sulfur output from the ion source (36S?/35Cl? ≈ 4 × 10?10 for samples prepared from chemically pure reagents), and a possibly cross contamination resulted in a background corresponding to 36Cl/Cl ≈ 3 × 10?14. The method was applied to samples containing between 105 and 106 atoms 36Cl/g rock from sites in Italy and Iran, which were already investigated by other laboratories for surface exposure dating. The 36Cl/Cl ratios in the range from 2 × 10?13 to 5 × 10?12 show a generally good agreement with the previous results.These first measurements demonstrate that also 3-MV tandems, constituting the majority of dedicated AMS facilities, are capable of 36Cl exposure dating, which is presently the domain of larger facilities. |
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