Universität zu Köln

Gwozdz, Martina Anna ORCID: 0000-0001-8248-1423 (2026). Advanced Radiocarbon Analysis of Environmental Samples at the 6 MV AMS System of CologneAMS. PhD thesis, Universität zu Köln.

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Abstract

Compared with conventional 14C AMS (Accelerator Mass Spectrometry), in which samples are converted into graphite with around 1000 mug C, direct CO2 gas measurements enable the analysis of samples with less than 200 mug C. This becomes increasingly important for environmental and archaeological applications. At the 6 MV AMS system at the University of Cologne, the established EA-GIS-AMS setup and the newly developed COMORI (COmbustion and Measurement Of Radiocarbon and stable Isotopes) system are used for advanced small 14CO2 analysis. This thesis evaluates the performance of the COMORI setup and investigates the influence of delta13C corrections on conventional radiocarbon ages measuring 103 samples from three different IAEA standards. Replacing the delta13C value in the conventional radiocarbon age calculation with IRMS-derived values improves the average conventional radiocarbon ages of many samples, although the effect is limited by counting statistics in CO2 AMS measurements. Reliable measurements are achieved for sample masses down to about 10 mug carbon, and a new cleaning routine improved the blank level from 14C/12C = 0.0127 ± 0.0012 to 0.00392 ± 0.00215. A constant contamination model yields F14C = 0.87 ± 0.22, consistent with the previous (EA-GIS) system value of F14C = 0.93 ± 0.23. The first application of COMORI investigates the suitability of CO2 AMS measurements for dendrochronologically dated tree rings and compares them with graphite measurements. Conventional radiocarbon age uncertainties range from 59–63 years for CO2 measurements and 38–39 years for graphite targets due to improved counting statistics. After OxCal modelling, both approaches yield statistically robust calibrated ages. Radiocarbon measurements were further applied to Late Glacial pine wood discovered at Schloss Neuhaus in Paderborn, Germany, to investigate the chronology of Allerød deposits. More than 80 pine trunks were grouped into seven dendrochronological sequences and dated using CO2 and graphite AMS measurements. The modelled ages indicate that the trees span roughly 600 years from about 13 500 calBP to 13 040 calBP. Their spatial distribution and trunk orientations suggest deposition during multiple fluvial transport events, providing a rare radiocarbon archive of Late Glacial pine wood. The second application addresses the measurement of activated graphite samples, in the context of nuclear waste management, where sample dilution prior to AMS analysis is required to avoid contamination of the system. Both mechanical dilution with dead graphite and gas dilution were investigated. Although mechanically diluted samples show lower measurement scatter (≈3 %) than gas-diluted samples (≥11 %), gas dilution offers a flexible and practical approach and proves suitable for the reliable measurement of activated graphite.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Gwozdz, Martina Anna martina.gwozdz@t-online.de https://orcid.org/0000-0001-8248-1423 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-804893
Date:	2026
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Physics > Institute for Nuclear Physics
Subjects:	Physics
Uncontrolled Keywords:	Keywords Language AMS English EA IMRS English Radiocarbondating English
Date of oral exam:	10 June 2026
Referee:	Name Academic Title Mücher, Dennis Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/80489