Ghostly glow of nuclear power plant detected in pristine water 150 miles away: ScienceAlert

In 2018, a reservoir of the purest water, buried under kilometers of rock in Ontario, Canada, flashed as barely detectable particles crashed through its molecules.

It was the first time water had been used to detect a particle known as an antineutrino, which originated from a nuclear reactor more than 240 kilometers (150 miles) away. This is an amazing breakthrough Neutrino Experiments and observational technology that use inexpensive, safe, and easily obtainable materials.

As one of the most abundant particles in the universe, Neutrinos They are strange little things with great potential to reveal deeper insights into the universe. Unfortunately, they are almost massless, carry no charge, and barely interact with other particles at all. They mostly flow through space and rocks alike, as if all matter were immaterial. There's a reason they're known as ghost particles.

Antineutrinos are the particle counterpart of antineutrinos. Normally, an antiparticle has an opposite charge to its equivalent particle; The antiparticle of a negatively charged electron, for example, is a positively charged positron. Since neutrinos carry no charge, only scientists can distinguish between the two Based on the truth The electron neutrino will come into existence along with the positron, while the electron neutrino will come into existence along with the electron.

Electron antineutrinos emit During nuclear beta decay, which is a type of radioactive decay in which a neutron decays into a proton, an electron, and an antineutrino. An electron antineutrino can then interact with a proton to produce a positron and a neutron, a reaction known as reversible beta decay.

Large tanks filled with liquids and lined with photomultiplier tubes are used to detect this type of decomposition. They are designed to capture the dim glow of Cherenkov radiation They are created by charged particles moving faster than light can travel through a liquid, similar to the sonic boom caused by breaking a sound barrier. So they are very sensitive to very dim light.

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

He enters Snow +. It is buried under more than 2 kilometers (1.24 mi) of rock, and is the deepest underground laboratory in the world. This rock shielding provides an effective barrier against cosmic ray interference, allowing scientists to obtain exceptionally well-resolved signals.

Today, the laboratory's 780-ton spherical tank is filled with linear alkylbenzene, a liquid scintillator that amplifies light. In 2018, while the facility was undergoing calibration, it was filled with ultra-pure water.

By looking at data collected over 190 days during the calibration phase in 2018, the SNO+ collaboration found evidence of inverse beta decay. The neutron produced during this process is captured by the hydrogen nucleus in the water, which in turn produces a soft glow of light at a very specific energy level, 2.2 MeV.

Cherenkov water detectors generally have difficulty detecting signals below 3 MeV; But water-filled SNO+ 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 would be worth their luck to look for signs of inverse beta decay.

Analysis of the candidate signal determined that it was likely produced by an antineutrino, with a confidence level of 3 sigma – a 99.7% probability.

The result suggests that water detectors could be used to monitor energy production in nuclear reactors.

Meanwhile, SNO+ is being used to help better understand neutrinos and antineutrinos. Because neutrinos exist It is impossible to measure it directlywe I don't know much about them. One of the biggest questions is whether neutrinos and antineutrinos are exactly the same particle. A rare, never-before-seen decay will answer this question. SNO+ is currently researching this decay.

“It is interesting that pure water can be used to measure antineutrinos from reactors and at such large distances.” said physicist Logan Lipanowski From the SNO+ collaboration and the University of California, Berkeley, in March 2023.

“We made a great effort to extract a small number of signals from 190 days of data. The result was satisfactory.”

The research was published in Physical review letters.

A version of this article was first published in April 2023.