Progress report on a novel in situ¹⁴C extraction scheme at the University of Cologne

We present initial results of in situ¹⁴C system blank and calibration sample measurements obtained using the in situ¹⁴C extraction scheme developed at the University of Cologne. The ¹⁴C extraction scheme specifically exploits the phase transformation of quartz to cristobalite in order to quantitatively extract the carbon as CO₂ and follows a scheme that is different to that of existing extraction systems. Features are offline furnace extraction, single pass catalytic oxidation using mixed copper (I,II) oxide as catalyst, the use of UHV-compatible components and of vacuum annealed copper tubing. The design allows a relatively rapid sample throughput – two samples per day as opposed to the current 2 days per sample that can be done on other lines – and can accommodate samples ranging between 0.5 and 4 g of clean quartz. Following extraction and cleaning, the CO₂ gas is measured using the gas ion source of the MICADAS AMS facility at ETH Zurich. The extraction system yields low systems blanks (10 ⁺¹⁶/₋₁₀ × 10³ atoms ¹⁴C, ±1 σ) and the initial results indicate that further improvements are achievable. Measurements of the CRONUS-A standard sample show a good reproducibility and results are consistent with published values. We also present the first in situ¹⁴C results for the CRONUS-R standard material.