DEUTERON ACTIVATION-ANALYSIS FOR THE DETERMINATION OF CARBON IN IRON AND COPPER-OXIDE, REAGENTS FOR C-14 DATING BY ACCELERATOR MASS-SPECTROMETRY

In the C-14-dating by accelerator mass spectrometry (AMS) iron and cop per oxide are used during sample preparation. In an investigation on t he origin of the C-14-blank, which in practice determines the dating l imit of AMS, the carbon contamination was measured in both reagents by deuteron activation analysis via the C-12(d,n)N-13 reaction. A first batch of iron was analysed radiochemically and a carbon concentration of 37.6 mu g/g was found with a standard deviation of 2.7 mu g/g (3 an alyses). In a second batch of iron concentrations between 66 and 150 m u g/g were found for 6 instrumental analyses, suggesting an inhomogene ous distribution of carbon. The carbon content in copper oxide was 17. 8 (3.5) mu g/g for 3 instrumental analyses, but preference should be g iven to a radiochemical analysis. These figures indicate that the carb on impurities found in iron and copper oxide are possible causes of th e C-14-blank. However, a final conclusion can only be drawn if the C-1 4 concentration of the contaminating carbon and the amount of carbon r eleased during sample preparation are known.