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Status report on target preparation for 14C AMS dating in the Zagreb radiocarbon Laboratory

A new rig for graphite target preparation for 14C dating by AMS was implemented in the Zagreb Radiocarbon Laboratory in 2008. Graphites are prepared by oxidation of organic samples with CuO on 850°C or by hydrolization of carbonate samples with acid and then by converting the obtained CO2 to graphite on iron powder in reaction with Zn on 450°C. The samples in form of graphite-iron powders are sent to the Scottish Universities Environmental Research Centre (SUERC), Glasgow, UK, where they are pressed into aluminium carriers (targets) and measured for 14C on AMS. Technical details and the results from the test and validation series have already been presented [1]. A batch of samples prepared during the further validation phase showed increased background levels probably caused by an inappropriate position of the graphitization rig. Therefore, it was moved into an adapted and isolated “clean” room. The next batch of background and standard samples proved that this location is suitable for producing contamination free graphite powders for 14C AMS measurements showing age limit detection of 51 000 years BP. Each step in graphite preparation was separately tested using background materials in different forms (borehole CO2 gas, anthracite, the “Heidelberg wood” and the Carrara marble). For final validation a set of graphite targets was prepared from various types of samples (linen, collagen, wood, charcoal, dissolved inorganic carbon and shells) of known 14C activities that have already been determined either by liquid scintillation counting (LSC), routinely used in our laboratory, or within the VIRI intercomparison. The comparison of 14C AMS results with the LSC and VIRI values showed a good agreement.

14C dating; AMS

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