Preparation of Graphite Targets in the Gliwice Radiocarbon Laboratory for AMS 14C Dating

Abstract

A line for preparation of graphite targets for accelerator mass spectrometry (AMS) radiocarbon dating has been built in the Gliwice 14C Laboratory. The AMS 14C measurements of our targets are performed in the Leibniz-Labor fur Altersbestimmung, Kiel, Germany. The quality of our line has been tested in two series of AMS 14C measurements of background and Ox-II standard samples and by measurements of the amount of CO2 released during combustion of sample-free quartz tubes. Most background contamination in the first series was introduced during combustion, which has been greatly reduced by baking quartz tubes vacuum-sealed with CuO and Ag. The residual contamination (ca. 1.5 micrograms C) seems to come mostly from the quartz tubes themselves. At present, most of the contamination of the background is introduced during graphitization. The reproducibility of background preparations is satisfactory, especially for samples larger than 1.5 mg, when it is better than +/0.09 pMC. Despite still significant contamination with low-14C carbon during the graphitization process (corresponding to 1.2 +/0.2% of 14C-free carbon), the good reproducibility of the results allows us to use our line in routine 14C dating.