Deuteron activation analysis for the determination of carbon in iron and copper oxide, reagents for¹⁴C-dating by accelerator mass spectrometry

Abstract

In the¹⁴C-dating by accelerator mass spectrometry (AMS) iron and copper oxide are used during sample preparation. In an investigation on the origin of the¹⁴C-blank, which in practice determines the dating limit of AMS, the carbon contamination was measured in both reagents by deuteron activation analysis via the¹²C(d,n)¹³N reaction. A first batch of iron was analysed radiochemically and a carbon concentration of 37.6 μg/g was found with a standard deviation of 2.7 μg/g (3 analyses). In a second batch of iron concentrations between 66 and 150 μg/g were found for 6 instrumental analyses, suggesting an inhomogeneous distribution of carbon. The carbon content in copper oxide was 17.8 (3.5) μg/g for 3 instrumental analyses, but preference should be given to a radiochemical analysis. These figures indicate that the carbon impurities found in iron and copper oxide are possible causes of the¹⁴C-blank. However, a final conclusion can only be drawn if the¹⁴C concentration of the contaminating carbon and the amount of carbon released during sample preparation are known.