Simple water can be used to detect nuclear reactor neutrinos


Neutrinos are subatomic particles that interact very weakly with matter. They are produced in many types of radioactive decay, including in the Sun’s core and nuclear reactors. Blocking neutrinos is also impossible—they travel easily from the core of the reactor to a detector far away, and even through Earth. Detecting even the smallest signals from neutrinos requires large, highly sensitive devices. Although the neutrinos produce only small signals in the detector, the SNO+ experiment shows that a simple water-filled detector can still detect nuclear neutrinos.


The SNO+ measurement shows that remote nuclear reactors can be monitored with something as simple and cheap as water. Nuclear reactors cannot shield the neutrinos they produce. That is, the measurement of SNO+ is proof of concept that such water detectors can play a role in ensuring nonproliferation. As with SNO+, such detectors would need to be extremely clean of any radioactivity, large (SNO+ contains 1,000 tons of water), and able to detect the tiny amounts of light produced by neutrinos. However, the use of water means that much larger detectors are possible and a real option to „see” even the most distant reactors.


Scientists have long thought that the tiny signals (just 10-20 photons) produced by nuclear neutrinos in water detectors would make it impossible to detect those neutrinos, especially since the rate of these signals is so low when the detector is far from the reactor. . By ensuring that the detector was clean of trace levels of radioactivity, and having a lower energy range than any water detector ever built, SNO+ was able to see these signals and show that they came from nuclear reactors at least 240 kilometers (150 miles) away. ) far away. The measurement was even more difficult due to the background of residual radiation (pseudo-events) and neutrinos created in the atmosphere by cosmic rays, which had to be detected and removed.

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Water detectors have many advantages. They are cheap and quite large, making them useful for monitoring reactors across international borders. Improvements to such monitoring, including using a water-based liquid scintillator or „loading” water with gadolinium, are being tested by other collaborations. This work stems from the SNO+ collaboration, an international collaboration of about 100 scientists from the United States (University of Pennsylvania, University of California at Berkeley and Lawrence Berkeley National Laboratory, University of California at Davis, Brookhaven National Laboratory, Boston University, and University of Chicago), Canada, United Kingdom, Portugal, Germany, China and Mexico. SNO+ is located at SNOLAB, Canada’s underground laboratory.


SNO+ received funding from the Department of Energy’s Office of Energy, Office of Nuclear Physics, and the National Science Foundation and the Department of Energy’s National Nuclear Security Administration through the Nuclear Science and Security Program. Funding in Canada: Canada Foundation, Natural Sciences and Engineering Research Council, Canadian Institute for Advanced Research, Queen’s University, Ontario Ministry of Research, Innovation and Science, Alberta Science and Research Investment Program, Central Economic Development Initiative. Northern Ontario, and Ontario Early Researcher Awards. In the United Kingdom, funding has been received from the Science and Technology Facilities Council, the European Union’s Seventh Framework Program under the European Research Council Grant Agreement and the Marie Curie Grant Agreement. Funding also came from Fundaçáo para a Ciência ea Tecnologia (FCT-Portugal), Deutsche Forschungsgemeinschaf in Germany, DGAPA-UNAM and Consejo Nacional de Ciencia y Tecnologia in Mexico, and Discipline of Construction University in China.


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