Cologne Noble Gas Mass Spectrometry
Complementing the CologneAMS facility for measuring 10Be, 26Al, 36Cl for terrestrial cosmogenic nuclide studies, our working group host a Helix MC Plus (Thermo Scientific) noble gas mass spectrometer dedicated to the measurement of cosmogenic noble gas isotopes. The Helix MC Plus is equipped with 5 Faraday Cups (1 x 1012 and 4 x 1013 Ω resistors) and 5 CDD Multipliers. In 2019 measurement protocols for cosmogenic neon were established and samples are now being analysed routinely.
Samples are heat-extracted utilizing an IR-fiber-laser (1064 nm, StarFiber 600, Rofin; power-tuneable between 20 and 600 W) that is equipped with a software-controlled galvanic scanning head (Rofin). Sample gases are purified via sequential exposure to two reactive metal getters (SAES) and a watertrap (Janis; held at 205 K); and separated using dual-head cryotrap (Janis; ≥24 K bare trap and ≥ 10 K charcoal filled trap; LakeShore Cryo-controller). For ease of operation, and reproducibility of results, the use of cooling liquids (e.g. C02-slush or liquid N2) is avoided for standard samples, while maintaining low backgrounds of relevant interferences. The purification and cryogenic separation of noble follows a fully-automated sequence, developed using LabView.
The system is geared for state of the art high‐precision (uncertainties < 0.5%) and trace analysis (detection limit < 50,000 atoms) of cosmogenic noble gas isotopes in quartz (21,22Ne) and He‐retentive minerals (3He; e.g. iron‐oxides, pyroxene, olivine). Utilizing intercomparison material (Vermeesch et al., 2015) the performance of the new system was found to be on par with its international peers (with respect to blanks, sensitivity & reproducibility).
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.