Cologne Noble Gas Mass Spectrometry

Complementing the CologneAMS facility for measuring ¹⁰Be, ²⁶Al and ³⁶Cl for terrestrial cosmogenic nuclide studies, our working group hosts a Helix MC Plus (Thermo Scientific) noble gas mass spectrometer dedicated to the measurement of cosmogenic noble gas isotopes.

The system was funded by the German Research Foundation (Project number 259990027) and is geared for state of the art high‐precision and trace analysis of cosmogenic noble gas isotopes in quartz (^21,22Ne), zircon (^78,81Kr) and He‐retentive minerals (³He; e.g. iron‐oxides, pyroxene, olivine). The performance of the system for cosmogenic neon analysis is on par with its international peers (Ritter et al. 2021; see also Fig. 9 of Györe et al. 2021, https://doi.org/10.3390/geosciences11080353). The system is the first installation to perform in-situ cosmogenic krypton measurements on terrestrial material (Dunai at al. 2022).

Samples are heat-extracted utilizing an IR-fiber-laser that is equipped with a software-controlled galvanic scanning head. Sample gases are purified via sequential exposure to two reactive metal getters and a watertrap, and separated using dual-head cryotrap. For ease of operation and reproducibility of results, the use of cooling liquids (e.g. CO₂-slush or liquid N₂) is avoided, while maintaining low backgrounds of relevant interferences. The purification and cryogenic separation of noble gases follows a fully automated sequence developed using LabView (Ritter et al. 2021).

- T.J. Dunai, S.A. Binnie and A. Gerdes 2022 In situ-produced cosmogenic krypton in zircon and its potential for Earth surface applications, Geochronology 4, 65–85, https://doi.org/10.5194/gchron-4-65-2022
- B. Ritter, A. Vogt and T.J. Dunai 2021 Technical Note: Noble gas extraction procedure and performance of the Cologne Helix MC plus multi-collector noble gas mass spectrometer for cosmogenic neon isotope analysis, Geochronology 3, 421–431, https://doi.org/10.5194/gchron-3-421-2021

In-situ cosmogenic ¹⁴C Laboratory

The use of in-situ cosmogenic ¹⁴C is a relatively new method of analysis which has a great potential for earth surface studies. With a half-life of 5.730 years it reaches saturation quickly, which makes it especially suitable to study short-term erosion rates and young burial histories (Holocene). In combination with longer-lived cosmogenic isotopes (¹⁰Be, ²⁶Al) in-situ cosmogenic ¹⁴C can be used to identify inheritance effects and determine complex exposure and erosion histories.
As a part of the CologneAMS facility for measuring isotopes for terrestrial cosmogenic nuclide studies (e.g. ¹⁰Be, ²⁶Al, ³⁶Cl), our working group has a laboratory dedicated to the extraction of in-situ ¹⁴C from quartz. The extraction scheme is based on the phase transformation of quartz to cristobalite in order to quantitatively extract the carbon as CO₂ (1).
The in-situ ¹⁴C extraction scheme has a modular design, which includes a vacuum line for removing of atmospheric ¹⁴C, an offline furnace extraction (1650 °C) and an all-metal UHV extraction system for gas purification and gas volume measurements. The later involves a single pass catalytic oxidation process that uses mixed copper (I,II) oxide as catalyst and is built with UHV-compatible components and vacuum annealed copper tubing.
A set of three parallel cracking units allows a relatively rapid sample throughput (an average time of one sample per day, including all the steps previous to the extraction process) and can accommodate samples ranging between 0.5 and 4 g of clean quartz. Following extraction and cleaning, the CO₂ gas is trapped in gas ampoules suitable for analysis at the Cologne 6 MV AMS system.
The measurement of blanks and standards has shown good sensitivity and reproducibility with a performance that is on par or better than that of its international peers (2).

(1) Fülöp, R-H., et al. "Progress report on a novel in situ ¹⁴C extraction scheme at the University of Cologne." Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 361 (2015): 20-24.
(2) Schiffer, Markus, et al. "Method developments for accelerator mass spectrometry at CologneAMS, ⁵³Mn/³He burial dating and ultra-small ¹⁴CO₂ samples." Global and Planetary Change 184 (2020): 103053.