Water Detector Captures Antineutrinos From Reactor 150 Miles Away
Scientists at the underground SNO+ laboratory reported the first detection of reactor antineutrinos using pure water, demonstrating a low-cost method for remote monitoring of nuclear reactors.
Researchers at the SNO+ experiment, located more than two kilometres beneath the Earth's surface in Ontario, Canada, have recorded the faint glow produced when an antineutrino from a nuclear power plant 240 kilometres away interacted with ultrapure water inside a 780-tonne tank. The detection was made while the detector was temporarily filled with water during a 2018 calibration run, and analysis of 190 days of data revealed a signal consistent with inverse beta decay at an energy of 2.2 MeV, with a statistical confidence of three sigma (about 99.7%).
"It intrigues us that pure water can be used to measure antineutrinos from reactors and at such large distances," said physicist Logan Lebanowski of the SNO+ collaboration and the University of California, Berkeley.
The finding, published in Physical Review Letters, marks the first time that water alone has been used to detect antineutrinos from a distant reactor, a task previously limited to large liquid scintillator detectors. The result suggests that simpler, cheaper water-based detectors could be deployed for remote monitoring of nuclear reactor activity and for fundamental neutrino research. SNO+ has since returned to its scintillator phase and continues to study low-energy neutrino interactions, including recent observations of solar neutrinos converting carbon-13 to nitrogen-13.
The experiment benefits from the deep underground location, which shields the detector from cosmic-ray background, allowing it to sense the weak Cherenkov light produced by the reaction. The team estimates a detection efficiency of about 50 % for the 2.2 MeV signal, extending the observable energy range below the typical 3 MeV threshold for water detectors.
