Sudbury Neutrino Observatory
In 1984, Herb Chen of the University of California at Irvine first pointed out the advantages of using heavy water as a detector for solar neutrinos.
[3][4] The Creighton Mine in Sudbury is among the deepest in the world and, accordingly, experiences a very small background flux of radiation.
It was quickly identified as an ideal place for Chen's proposed experiment to be built,[3] and the mine management was willing to make the location available for only incremental costs.
At the time it competed with TRIUMF's KAON Factory proposal for federal funding, and the wide variety of universities backing SNO quickly led to it being selected for development.
The experiment observed the light produced by relativistic electrons in the water created by neutrino interactions.
The SNO detector target consisted of 1,000 tonnes (1,102 short tons) of heavy water contained in a 6-metre-radius (20 ft) acrylic vessel.
The heavy water was viewed by approximately 9,600 photomultiplier tubes (PMTs) mounted on a geodesic sphere at a radius of about 850 centimetres (28 ft).
In the neutral current interaction, a neutrino dissociates the deuteron, breaking it into its constituent neutron and proton.
This interaction is the relativistic equivalent of billiards, and for this reason the electrons produced usually point in the direction that the neutrino was travelling (away from the sun).
Because this interaction takes place on atomic electrons it occurs with the same rate in both the heavy and light water.
The first scientific results of SNO were published on 18 June 2001,[8][9] and presented the first clear evidence that neutrinos oscillate (i.e. that they can transmute into one another), as they travel from the Sun.
[10] In 2015 the Nobel Prize for Physics was jointly awarded to Arthur B. McDonald, and Takaaki Kajita of the University of Tokyo, for the discovery of neutrino oscillations.
SNO was a founding member of the Supernova Early Warning System (SNEWS) with Super-Kamiokande and the Large Volume Detector.
