36Cl exposure dating with a 3-MV tandem
Date
2010
Authors
Steier, Peter
Forstner, O
Golser, Robin
Kutschera, Walter
Martschini, M.
Merchel, S.
Orlowski, Tobias
Priller, Alfred
Vockenhuber, C.
Wallner, Anton
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Elsevier
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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Keywords: Cross contamination; Isobar separation; Isotopic concentrations; Surface exposure dating; Tandem accelerators; Terminal voltages; Ion sources; Sulfur; Isotopes 36Cl; AMS; Isobar separation
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Nuclear Instruments and Methods in Physics Research: Section B
Type
Journal article
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2037-12-31
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