SNO+ captures first reactor neutrinos detected by water

March 06, 2023 — Experiment Updates

Even before it’s completed, the SNO+ experiment at Sudbury’s SNOLAB has made a discovery, one that can assist in monitoring nuclear power stations around the world.

While filled with ultrapure water as the detector’s components were being upgraded in 2018, 190 days of data yielded results that surprised the experiment team and is a first in the field of astroparticle physics.

In the data was an antineutrino signal that came from the Bruce, Darlington and Pickering nuclear generating stations hundreds of kilometres away.

SNO+ event display

Antineutrinos are produced as a byproduct of fission — when a neutron decays into a proton and an electron in nuclear reactors. Being able to see these antineutrinos in ultrapure water was unexpected. This suggests it is possible to use neutrino detectors such as SNO+ to continuously monitor a reactor’s power production from a great distance.

The finding also suggests it is possible to build neutrino detectors with ultrapure water, a non-toxic, inexpensive and easy-to-handle material. These are key factors in developing the ability to audit nuclear reactors around the world.

“It intrigues us that pure water can be used to measure antineutrinos from reactors and at such large distances,” said SNO+ collaboration member Logan Lebanowski.

“We spent significant effort to extract a handful of signals from 190 days of data,” Lebanowski said.  “The result is gratifying.”

The SNO+ experiment is an upgrade of the award-winning Sudbury Neutrino Observatory (SNO) experiment. The five-storey tall experiment vessel is currently filled with a liquid scintillator (much like a mineral oil) that produces light up when charged particles pass through it.

SNO+ experiment cavity

“This finding is a great indicator that we can expect very exciting physics from the scintillator phase, running now for nearly 10 months, well into the future,” said SNOLAB research scientist Christine Kraus.

The SNO+ detector will search for a so-far-undetected nuclear-decay process. Spotting this rare decay would allow researchers to confirm the neutrino is its own antiparticle. A paper detailing the SNO+ findings, “Evidence of Antineutrinos from Distant Reactors using Pure Water at SNO+” will be published by the American Physical Society’s Physics Magazine on March 9, 2023. A synopsis of the paper can be found here.