⁴He/³He Thermochronology Laboratory  

Overview

The Potsdam ⁴He/³He Thermochronology Laboratory at the University of Potsdam, Germany, is dedicated to the high-precision measurement of ⁴He and ³He noble gas abundances and isotopic ratios (i.e. ⁴He³He) in U-bearing accessory minerals such as apatite.

The laboratory is equipped with a Helix SFT Thermo Scientific mass spectrometer recently acquired and funded by the European Research Council (ERC). The Helix SFT is connected to a Thermo extraction and purification Prepline dedicated to mineral samples for routine analysis with a single-head cryotrap (planned to be installed at the end of May 2021). The Prepline is equipped with an inlet cell for Diode Laser fusion and/or step heating. The upcoming cryotrap (planned in May) will allow the separation of He from other noble gases (i.e., Ne, Ar, K,r, and Xe). The purification system includes 4 NP10 getters.
The Helix SFT is specifically designed to analyze 4He and 3He in multi-collection mode with 1 CDD and 1 Faraday’s cup.

Once the gases have been extracted from a sample, all clean-up and cryogenic separation procedures will be fully automated by a computer-controlled system. The computer that controls the automation and the extraction benches runs under LabView, which allows the user to also fully manually control the system. The entire system will be designed by multi-threaded control software from the LabView computer, which allows for communication between Labview and Teledyne (Diode Laser) software with the Thermo Helix SFT (Qtegra).

Developing a world-leading ⁴He and ³He thermochronology facility in Europe: Project Detail

We are building a ⁴He and ³He thermochronology facility in Potsdam by acquiring a high-resolution noble-gas mass-spectrometer. The Helix SFT from ThermoFisher Instruments provides a sensitivity >2×10⁴ Amps / Torr required to measure extremely small amounts of ⁴He and ³He. The split-flight tube design allows measuring both isotopes simultaneously in multi-collection mode (low mass on a multiplier, high mass on a Faraday detector) or by peak jumping in single collector mode (in case of very low ⁴He abundances). A noble-gas preparation line is acquired together with the mass spectrometer, ensuring optimum efficiency in the setup. The line includes a diode-laser heated sample cell for precise step-heating and a cryogenic cold-trap for separating He from Ne while at the same time concentrating He before expansion into the mass spectrometer to enhance detection. Collaborations with European-based facilities for proton irradiations are currently being set up. Our ambitious project is to ensure that proton irradiation can be performed at the fluences required for successful ⁴He and ³He analyses (10¹⁵–10¹⁶protons/cm², corresponding to ~5-10 hours irradiation per sample batch). U-Th(-Sm) measurements required for dating will be carried out on an inductively-coupled plasma mass spectrometer (ICP-MS) already installed at Potsdam. The development of this unique ⁴He and ³He thermochronology facility constitutes the core of the COOLER project. This will be the first purpose-built ⁴He and ³He thermochronology facility worldwide, and it is expected to set a new level in sensitivity, resolution, and efficiency of the technique (in particular through the possibility of measuring samples in multi-collector mode). We will experiment with new proton-irradiation routines designed to solve the challenge of limited capacity that has hindered the development of ⁴He and ³He thermochronology in the last years, as well as with routine electron-microscope scanning of samples to map out U-Th distributions.

Current status

The Laboratory has an operating Diode laser, a 10K cryotrap connected to a Thermo Prep-line and a Helix SFT.
Our Janis 10K cryotrap is operational, and the line has been cross-calibrated with Durango Apatite with a U/Th-He age measured at 30.17 ±1.03Ma over 10 samples. The analytical protocol is carried out under Labview software with full automation from laser extraction to mass spectrometer analysis.
The facility has been fully operational since 2022 and supports analyses of ⁴He/³He profiles in Apatite grains.