Sudbury Neutrino Observatory
The Sudbury Neutrino Observatory (SNO) is a neutrino observatory in an old nickel mine near Sudbury , Ontario , Canada that went into operation in May 1999 . The detector was switched off on October 28, 2006, and the data obtained have been analyzed since then. At the same time, it was planned to use the infrastructure for further experiments, which will be continued with the experiment SNO plus ( SNO + , SNOplus ). In particular, the scintillator in the SNO-plus experiment will be linear alkylbenzene (LAB), a raw material for surfactants. New commissioning should be in 2014.
Arthur Bruce McDonald , who received the Nobel Prize in Physics in 2015 for the discovery of neutrino oscillations , has been the director of the observatory since 1989 .
The heart of the SNO is the detector , which is located more than 2000 m below the earth's surface and contains 1000 t heavy water (D 2 O) in a spherical tank made of acrylic glass. The tank is completely immersed in a basin with normal, ultrapure water for shielding and mechanical stabilization. Because the detector is so deep under the earth's surface, it is very well shielded from cosmic rays. Due to the weak interaction of neutrinos with matter, they are the only particles that reach the detector almost unhindered. Electron neutrinos react with the neutrons of the deuterium in the molecules of heavy water to form a proton and an electron (neutrino-induced beta decay ). When the electrons pass through the water, Cherenkov radiation is generated , which is detected by approx. 9600 photomultipliers arranged around the tank .
Muon and tau neutrinos cannot trigger the aforementioned reaction, but can be detected in the detector by reactions of the elastic neutrino scattering on electrons or by the disintegration of deuterium into protons and neutrons. This enables a distinction between electron neutrinos and the other neutrinos. Only then could the solar neutrino problem (too low measurement rates for electron neutrinos) be experimentally explained using the theory of neutrino oscillation , since the missing electron neutrinos could be detected as muon or tau neutrinos. Recent measurements have shown that the total neutrino flux (electron, muon and tau neutrinos) agrees very well with the expectation from the standard solar model. With this, neutrino oscillations have been proven beyond doubt.
Individual evidence
Web links
Coordinates: 46 ° 29 ′ 26 ″ N , 80 ° 59 ′ 39 ″ W.