In an unprecedented achievement, the SNO+ experiment has showcased the ability to identify neutrinos emitted from a nuclear reactor stationed over 240 km distant using mere water.
Neutrinos are elementary particles that display extremely feeble interaction with matter. They stem from diverse forms of radioactive decay, such as those taking place within the heart of the sun and in nuclear reactors. Moreover, it’s not feasible to obstruct neutrinos; they can easily traverse from a nuclear reactor’s core to a remote detector, even capable of piercing the Earth itself. Therefore, to seize the tiny signals from neutrinos, apparatus of colossal scale and high precision are required. The SNO+ experiment recently proved that a detector filled simply with water can discern reactor neutrinos, notwithstanding the fact that the neutrinos generate only minute signals in the detector.
The SNO+ observation indicates that remote nuclear reactors can be scrutinized and tracked using something as basic and affordable as water. Reactors are incapable of shielding the neutrinos they emit. This implies that SNO+’s observation validates the concept that such water detectors could contribute to ensuring nuclear non-proliferation. Like SNO+, such detectors would still necessitate being immaculately clean of any radioactivity, large (SNO+ holds 1,000 tons of water), and able to register the diminutive amount of light that neutrinos produce. The application of water, however, signifies that extremely large detectors are feasible and a genuine option for “observing” even very remote reactors.
Researchers previously assumed that the microscopic signals (only 10-20 photons) generated by reactor neutrinos in a water detector would render it unfeasible to recognize those neutrinos, particularly when the detector was significantly remote from the reactor and the rate of these signals was extremely low. By assuring that the detector was devoid of even trace levels of radioactivity, and by having an energy threshold lower than any water detector ever constructed, SNO+ managed to perceive these signals and demonstrate that they originated from nuclear reactors at a minimum of 240 kilometers (150 miles) away.
The measurement was still relatively challenging, as backgrounds (false events) from residual radioactivity, and from neutrinos formed in the atmosphere by cosmic rays, needed to be distinguished and eliminated. Water detectors carry several benefits. They are economical and can be very extensive, making them beneficial for overseeing reactors across international boundaries. Enhancements to such monitoring, including the use of water-based liquid scintillators or “charging” the water with gadolinium, both aimed to amplify the signal size, are currently being examined by other teams.