Artist's concept of SNO's detector. (Courtesy of SNO)
The Sudbury Neutrino Observatory (SNO) is located 6800 feet (about 2 km) underground in an active nickel mine (INCO's Creighton Mine) in Greater Sudbury, Ontario, Canada. The detector is designed to detect solar neutrinos through their interactions with deuterium nuclei. The detector target is 1000 tonnes of heavy water contained in a 6 meter radius acrylic vessel, and the detector cavity is filled with light water to provide buoyancy for the vessel and radioactive shielding. The heavy water is viewed by approximately 9600 single photon detectors known as photomultiplier tubes (PMTs) mounted on a geodesic sphere at a radius of about 850cm. The experiment does not directly detect neutrinos, but rather observes the light produced by relativistic electrons in the water. As relativistic electrons lose energy they produce a cone of blue light through the Cerenkov effect, and it is this light that is directly detected. The detector was designed to solve the solar neutrino problem, as well as to search for evidence of neutrino flavour change (neutrino oscillation). SNO was the first solar neutrino detector capable of detecting all three neutrino flavours, and this capability is what allowed it to solve the solar neutrino problem.
The first measurements of the number of solar neutrinos reaching the earth were taken in the 1960s, and all experiments prior to SNO observed a third to a half fewer neutrinos than were predicted by the Standard Solar Model. One of the possible explanations for the reduced flux was the theory of neutrino flavor oscillation: the neutrinos emitted by the sun would undergo fundamental changes into other types of neutrinos as they travel to the Earth. On June 18, 2001, the first scientific results of the Observatory were published [1][2], bringing the first clear evidence that neutrinos change flavour as they travel through the sun. The total flux of all neutrino flavours measured by SNO agrees well with the theoretical prediction. Further measurements carried out by the Observatory have since confirmed the original result
SNO is also capable of detecting a supernova within our galaxy. As neutrinos emitted by a supernova are released earlier than the photons, it would be possible to alert the astronomical community before the supernova was visible. SNO is a founding member of SNEWS with Super-Kamiokande and LVD.
Asteroid (14724) SNO is named in honour of the Observatory.
The Sudbury Neutrino Observatory is a major setting in the Neanderthal Parallax trilogy by Canadian science fiction author Robert J. Sawyer.
Participating institutions
Large particle physics experiments require large collaborations. With approximately 100 collaborators SNO is a rather small group compared to collider experiments. The participating institutions include:
Canada
Although no longer a collaborating institution, Chalk River Laboratories led the construction of the acrylic vessel that holds the heavy water.
United Kingdom
United States of America
See also
Other neutrino observatories
Related Articles
External links
