Radiocarbon measurement using a gas/solid hybrid ion source and an automated sample preparation system at the University of Tsukuba

Abstract

The first preliminary test of the 14C-accelerator mass spectrometry (AMS) system at the University of Tsukuba was successfully performed using a gas/solid hybrid ion source and an automated sample preparation system with an elemental analyzer (EA). The maximum 12C− current of ∼11 µA was achieved using the optimized CO2 flow rate to the hybrid ion source. The machine background of 14C/12C for the AMS system reached to ∼2.4 × 10−16 (∼0.02 percent modern carbon, pMC) using unprocessed mineral graphite. Moreover, the blank level of 14C/12C including the combustion process for an IAEA-C1 graphite sample was 4.6 × 10−16 (0.05 pMC), demonstrating the low blank level of the automatic sample preparation system. In contrast, the blank level of 14C/12C including the combustion process for an IAEA-C1 CO2 sample was 5.0 × 10−15 (0.49 pMC), an order of magnitude worse than that for the graphite sample. The measurement uncertainty for the gas ion source was 0.6%, 2–3 times worse than that for the solid ion source (0.2%–0.3%).