Capturing Elusive Anti-Neutrinos from Faraway Fission Reactors with Pure Water at SNO+

Neutrinos are incredibly abundant, yet their near-massless nature makes them incredibly elusive. Despite billions of these particles streaming towards Earth from sources such as the Sun, the majority pass through our bodies and the planet without ever interacting with them. This characteristic makes studying these fundamental particles quite challenging. However, recent findings from the researchers working on the SNO+ neutrino detector project suggest that we may soon experience a substantial improvement in our ability to detect neutrinos.

In an early draft article submitted to the American Physical Society’s Review Letters, researchers unveil their groundbreaking findings. Utilizing the innovative SNO+ neutrino detection system, they have triumphantly observed anti-neutrinos generated by nuclear fusion facilities situated over 240 kilometers distant, encompassing both Canadian CANDU reactors and American LWR variants. This achievement demonstrates the low detection threshold of the SNO+ detector, even in its incomplete state between 2017 and 2019. The detector was initially filled with heavy water, and during the second run, nitrogen was added to prevent radioactive radon gas from seeping in from the surrounding rock in the deep mine shaft. SNO+’s 1.4 MeV core cutoff for Cherenkov detection is more than sufficient to identify the 2.2 MeV gamma rays from inverse beta decays (IBD), which is what the detector is intended to catch.

The SNO+ detector is an upgrade from the original Sudbury Neutrino Observatory (SNO), situated 2.1 km below the surface in the Creighton Mine. SNO operated from 1999 to 2006 and played a role in resolving the solar neutrino problem, ultimately uncovering the shifting nature of neutrinos through neutrino oscillation. Once completely filled with 780 tons of linear alkylbenzene as a scintillator, SNO+ will explore various subjects, including neutrinoless double beta decay (Majorana fermion), specifically addressing the puzzling question of whether neutrinos are their own antiparticles.

SNO+ focuses on nearby nuclear fission reactors due to the continuous beta decay that takes place in their nuclear fuel, producing numerous electron anti-neutrinos. This production occurs in a highly predictable manner, given the precise composition of nuclear fuel. As the researchers noted in their paper, SNO+ is accurate enough to detect when a specific reactor requires refueling based on changes in its anti-neutrino emissions. This property, however, does not affect Canadian CANDU PHWRs, as they are continuously refueled, resulting in a steady production of neutrinos. Each SNO+ experiment generates vast amounts of data (hundreds of terabytes per year) that takes time to process. Nonetheless, if these preliminary findings are any indication, SNO+ could advance neutrino research as significantly as SNO and its counterparts have done in the past.