The discovery of a "ghost glow" of a nuclear power plant in pure water 240 kilometers away!

Researchers have detected the flash of a reservoir of the purest water, buried under kilometers of rock in Ontario, Canada, as a barely detectable particle collided through its molecules.

This is the first time that water has been used to detect a particle known as an antineutrino, which originated from a nuclear reactor more than 240 kilometers (150 miles) away. This breakthrough promises neutrino experiments and observational technology that use materials that are inexpensive, easy to obtain, and safe.

As some of the most abundant particles in the universe, neutrinos are exotic little things with a lot of potential for revealing deeper insights into the universe. Unfortunately, they are almost massless, carry no charge, and hardly interact with other particles at all. They mostly flow through space and rock alike, as if all matter were insubstantial, so they are called ghost particles.

Antineutrinos are the antiparticle counterparts of neutrinos. Normally, an antiparticle has an opposite charge to the equivalent particle; The antiparticle of a negatively charged electron, for example, is the positively charged positron. Since neutrinos carry no charge, scientists can distinguish between the two based solely on the fact that an electron neutrino will appear alongside a positron, while an electron antineutrino will appear with an electron.

Electron antineutrinos are emitted during beta decay, a type of radioactive decay in which a neutron decays into a proton, an electron, and an antineutrino. One of these antineutrino electrons can interact with a proton to produce a positron and a neutron, a reaction known as inverse beta decay.

Large liquid-filled tanks lined with photomultiplier tubes are used to detect this particular type of decay. It was designed to capture the faint glow of Cherenkov radiation produced by charged particles traveling faster than light that can travel through a liquid, similar to the sonic boom caused by breaking the sound barrier.

Antineutrinos are produced in huge quantities by nuclear reactors, but they are relatively low in energy, which makes them difficult to detect.

and enter SNO+. Buried under more than 2 kilometers (1.24 miles) of rock, it is the world's deepest underground laboratory. This rocky shielding provides an effective barrier against cosmic ray interference, allowing scientists to obtain exceptionally well-resolved signals.

Today, the lab's 780-tonne spherical tank is filled with linear alkylbenzene, a flickering, light-amplifying liquid. Back in 2018, while the facility was undergoing calibration, it was filled with highly purified water.

Combing through 190 days of data collected during that calibration phase in 2018, the SNO+ collaboration found evidence of reverse beta decay. The neutron produced during this process is captured by a hydrogen nucleus in the water, which in turn produces a subtle burst of light at a very specific energy level, 2.2 MeV.

Cherenkov water detectors generally struggle to detect signals below 3 MeV; But SNO+ filled with water was able to detect up to 1.4 MeV. This results in an efficiency of about 50% for detecting signals at 2.2 MeV, so the team thought it was worth their luck looking for signs of inverse beta decay.

An analysis of a candidate signal determined that it was likely caused by an antineutrino, with a confidence level of 3 sigma - probability of 99.7%.

The result indicates that water detectors could be used to monitor the power production of nuclear reactors.

Meanwhile, SNO+ is being used to help better understand neutrinos and antineutrinos. Since it is impossible to measure neutrinos directly, we don't know much about them. One of the biggest questions is whether neutrinos and antineutrinos are exactly the same particles. A rare, never-before-seen dissolution would answer that question. SNO+ is currently looking for this decay.

"We're interested in the possibility of using pure water to measure antineutrinos from reactors over great distances," says physicist Logan Lipanovsky of the SNO+ Institute and University of California, Berkeley. "We made a great effort to extract just a few signals from 190 days of data. The result is satisfactory."

The research has been published in Physical Review Letters.