A Gas Ion Source for Radiocarbon Measurements at 200 kV

TLDR

The MICADAS system uses a hybrid Cs sputter negative ion source and a syringe‑based gas feeding setup that mixes CO₂ with He and delivers 3–30 µg of carbon continuously into the source for stable, quantitative radiocarbon measurements. The system achieves stable C⁻ currents up to 6 µA with 3–6 % efficiency, reproduces ¹⁴C/¹²C ratios within 1 % and ¹³C/¹²C within 0.2 %, and records blanks below 1 pMC.

Abstract

The novel tabletop miniaturized radiocarbon dating system (MICADAS) at ETH Zurich features a hybrid Cs sputter negative ion source for the measurement of solid graphite and gaseous CO 2 samples. The source produces stable currents of up to 6 μA C − out of gaseous samples with an efficiency of 3–6%. A gas feeding system has been set up that enables constant dosing of CO 2 into the Cs sputter ion source and ensures stable measuring conditions. The system is based on a syringe in which CO 2 gas is mixed with He and then pressed continuously into the ion source at a constant flow rate. Minimized volumes allow feeding samples of 3–30 μg carbon quantitatively into the ion source. In order to test the performance of the system, several standards and blanks have successfully been measured. The ratios of 14 C/ 12 C could be repeated within statistical errors to better than 1.0% and the 13 C/ 12 C ratios to better than 0.2%. The blank was <1 pMC.