SOURCES OF RADON CONTAMINATION IN C-14 DATING

We investigated the effect of radon (Rn-222) contamination of samples and chemicals used for sample preparation and gas purification on the C-14 age of samples. Radon count rate was monitored over several Rn-22 2 half-lives in a proportional counter filled with methane. We analyze d ca. 240 samples of fossil and recent wood, charcoal, bone, dissolved inorganic carbon in water, travertine, pest, aquatic plants, organic soil and atmospheric CO2 for Rn-222 contamination. Chemicals used for gas purification (MnO2, Mg(ClO4)(2)), ruthenium-coated pellets used fo r catalytic reduction of CO2 to CH4, and acids used for dissolution of calcareous samples (HCl and H3PO4) are also potential sources of Rn. Most geological samples contained a significant amount of Rn, as oppos ed to samples of wood, charcoal, aquatic plants and atmospheric CO2. W e also studied Rn contamination of water samples during tritium activi ty measurements in a CH4-filled gas proportional counter. We found an increased count rate in the H-3 channel, as well as above the 20 keV r egion in Rn-contaminated groundwater samples.