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The XENONnT dark matter detector has succeeded in performing measurements with nearly no radioactive interference. The technology was developed by a team led by particle physicist Prof Christian Weinheimer from the University of Münster.
In their search for dark matter, scientists from the XENON Collaboration are using one of the world’s most sensitive dark matter detectors, XENONnT at the Gran Sasso Laboratory of the National Institute of Nuclear Physics INFN in Italy, to detect extremely rare particle interactions. These could provide clues about the nature of dark matter. The problem, however, is that tiny amounts of natural radioactivity generate background events that can mask these weak signals. The XENONnT experiment has made a major breakthrough by significantly reducing one of the most problematic contaminants – radon, a radioactive gas. For the first time, the research team has succeeded in reducing the detector’s radon-induced radioactivity to a level a billion times lower than the very low natural radioactivity of the human body. The underlying technology, which the XENONnT consortium presents in the current issue of the Physical Review X, was developed by a team led by particle physicist Prof Christian Weinheimer from the University of Münster.
The XENONnT experiment measures the interactions of hypothetically predicted dark matter particles with atoms of liquid xenon, a noble gas. The 8.5-tonne detector operates at around minus 95 degrees Celsius deep below the Earth’s surface in order to eliminate as many background events as possible. The detector’s exceptional sensitivity is due to the extraordinary purity of the liquid xenon achieved thanks to the unique design of the detector and the use of ultra-radiopure materials. However, even traces of dissolved radon and its radioactive decay products can produce flashes of light that resemble the signals being sought. Since radon, a product of long-lived isotopes from the formation of our solar system, is present in virtually all materials, it accounts for a significant portion of the natural radiation exposure in humans.
To reduce radon events even further, the XENONnT team developed a cryogenic distillation system for the continuous purification of xenon. This process specifically removes radon and reduces its concentration in xenon by a factor of 4 to just 430 radon atoms per tonne of liquid xenon, as determined by the XENONnT group from Max Planck Institute für Nuclear Physics at Heidelberg. The background events caused by radon are thus about as rare as the extremely rare background caused by neutrinos, which originate from nuclear fusion inside the sun and cannot be shielded. Thanks to radon removal, measurements can be carried out with practically no radioactive background. “The technology paves the way for larger, even more sensitive detectors such as the planned XLZD liquid xenon observatory, which will be ten times larger,” explains Christian Weinheimer. “XENONnT brings us one step closer to solving the mystery of dark matter.”
Funding
As part of the ERC Advanced Grant project “LowRad,” funded by the European Research Council, Christian Weinheimer and his team are further developing the technology to significantly reduce radon and traces of other radioactive noble gases in xenon for XLZD. The Federal Ministry of Research, Technology and Space, formerly the Federal Ministry of Education and Research, and the German Research Foundation’s (DFG) research training group “Strong and Weak Interactions – From Hadrons to Dark Matter” supported the Münster team’s contribution to the XENONnT project.
Prof Christian Weinheimer
University of Münster
Institute for Nuclear Physics
Mail: weinheimer@uni-muenster.de
Aprile E. et al. (2025): Radon Removal in XENONnT down to the Solar Neutrino Level. Physical Review X 15, 031079; DOI: https://doi.org/10.1103/zc1w-88p6
The distillation plant ‘made in Münster’ for the dark matter experiment ‘XENONnT’ at the Gran Sasso ...
Source: Henning Schulze Eißing
Copyright: Henning Schulze Eißing
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The distillation plant ‘made in Münster’ for the dark matter experiment ‘XENONnT’ at the Gran Sasso ...
Source: Henning Schulze Eißing
Copyright: Henning Schulze Eißing
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