Small- to ultra-small-scale radiocarbon measurements using newly installed single-stage AMS at the University of Tokyo

Abstract

Small- to ultra-small-scale radiocarbon (14C) measurements are an essential technique for compound-specific radiocarbon measurements of fatty acids and amino acids. The Atmosphere and Ocean Research Institute at the University of Tokyo installed an NEC 250 kV single-stage accelerator mass spectrometer (AMS) in March 2013. We improved the pretreatment method to reduce modern and 14C-dead carbon contaminations. The modern and 14C-dead carbon contaminations from combustion and graphitization were estimated to be 0.37 ± 0.13 μgC and lower than 1.62 μgC, respectively. Furthermore, we examined an AMS measurement method that can be used to obtain a stable beam current intensity. As a result, we succeeded in conducting small- to ultra-small-scale 14C measurements. Typically, a sample of 100 µg of carbon (μgC) can be measured with a current of 25 μA in a low-energy Faraday cup for 30 min or more, whereas a sample of 10 μgC can be measured with a current of 1 μA in a low-energy Faraday cup for 15 min or more.