Zürich, Switzerland
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Nemec M.,University of Bern | Nemec M.,Laboratory of Ion Beam Physics | Nemec M.,Czech Technical University | Wacker L.,Laboratory of Ion Beam Physics | Gaggeler H.,University of Bern
Radiocarbon | Year: 2010

The reaction conditions for the graphitization of CO2 with hydrogen were optimized for a fast production of high-quality carbon samples for accelerator mass spectrometry (AMS) measurement. The iron catalyst in use is first oxidized by heating with air to remove possible carbon and other impurities and then after evacuation reduced back to iron with hydrogen in several flushing steps to remove any iron oxide. The optimum conditions for a fast graphitization reaction were experimentally determined by changing the reaction temperatures and the H2/CO2 ratio. The resulting graphite samples were measured by AMS to find the smallest isotopic changes (δ13C) at a minimum of molecular fragment formation (13CH current). The improvements are based on thermodynamic data and are explained with Baur-Glaessner diagrams. © 2010 by the Arizona Board of Regents on behalf of the University of Arizona.


Nemec M.,University of Bern | Nemec M.,Laboratory of Ion Beam Physics | Nemec M.,Czech Technical University | Wacker L.,Laboratory of Ion Beam Physics | And 2 more authors.
Radiocarbon | Year: 2010

The main methods applied to clean plant material for radiocarbon dating are not compound-specific and generally remove only the easily exchangeable components by an acid-base-acid sequence and additional optional steps like Soxhlet extraction to remove resins and oxidative bleaching with NaClO2. The products are normally clean enough for standard 14C measurement, but in some cases it is desirable to have pure cellulose, which remains unchanged and immobile over longer time ranges, better representing the original plant material. In this work, 2 more compound-specific but still simple methods were tested to separate the cellulose from wood. The viscose method is based on the xanthification process used in the textile industry, where the alkali-cellulose with CS2 forms a soluble cellulose xanthate, which is then extracted and cellulose is recovered. The second procedure is based on the wood/cellulose dissolution in ionic liquid 1-butyl-3-methylimidazolium chloride [BMIM]Cl, when the dissolved cellulose could be precipitated again by simply adding a water-acetone mixture. This process was recently reported, but still not used in sample preparation procedures for 14C dating. © 2010 by the Arizona Board of Regents on behalf of the University of Arizona.


Munsterer C.,Laboratory of Ion Beam Physics | Fohlmeister J.,Heidelberger Akademie der Wissenschaften | Christl M.,Laboratory of Ion Beam Physics | Schroder-Ritzrau A.,Heidelberger Akademie der Wissenschaften | And 4 more authors.
Geochimica et Cosmochimica Acta | Year: 2012

Monthly rain and drip waters were collected over a period of 10months at Bunker Cave, Germany. The concentration of 36Cl and the 36Cl/Cl-ratios were determined by accelerator mass spectrometry (AMS), while stable (35+37)Cl concentrations were measured with both, ion chromatography (IC) and AMS. The measured 36Cl-fluxes of (0.97±0.57)×10 4atomscm -2month -1 (0.97atomsm -2month -1) in precipitation were on average twice as high as the global mean atmospheric production rate. This observation is consistent with the local fallout pattern, which is characterized by a maximum at mid-latitudes. The stable chloride concentration in drip waters (ranging from 13.2 to 20.9mg/l) and the 36Cl-concentrations (ranging from 16.9×10 6 to 35.3×10 6atoms/l) are a factor of 7 and 10 above the values expected from empirical evapotranspiration formulas and the rain water concentrations, respectively. Most likely the additional stable Cl is due to human impact from a nearby urban conglomeration. The large 36Cl-enrichment is attributed to the local evapotranspiration effect, which appears to be higher than the calculated values and to additional bomb-derived 36Cl from nuclear weapons tests in the 1950s and 60s stored in the soil above the cave. In the densely vegetated soil above Bunker Cave, 36Cl seems not to behave as a completely conservative tracer. The bomb derived 36Cl might be retained in the soil due to uptake by minerals and organic material and is still being released now. Based on our data, the residence time of 36Cl in the soil is estimated to be about 75-85years. © 2012 Elsevier Ltd.

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