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History Construction of Kamioka Underground Observatory, the predecessor of the present Kamioka Observatory, Institute for Cosmic Ray Research, University of Tokyo began in 1982 and was completed in April, 1983. The purpose of the observatory was to detect proton decay, one of the most fundamental questions of elementary particle physics. The detector, named KamiokaNDE for Kamioka Nucleon Decay Experiment, was a tank which contained 3,000 tons of pure water and had about 1,000 photomultiplier tubes (PMTs) attached to the inner surface. The size of the tank was 16.0 m in height and 15.6 m in diameter. An upgrade of the detector was started in 1985 to allow the detector to observe solar neutrinos. As a result, the detector (KamiokaNDE-II) had become sensitive enough to detect neutrinos from SN 1987A, a supernova which was observed from in the Large Magellanic Cloud in February 1987. Solar neutrinos were observed in 1988 adding to the advancements in neutrino astronomy and neutrino astrophysics. The ability of the Kamiokande experiment to observe the direction of electrons produced in solar neutrino interactions allowed the experimenters to directly demonstrate for the first time that the sun was a source of neutrinos. Despite its success in neutrino observation, Kamiokande did not detect proton decay, its first aim. Also, even higher sensitivity was needed to observe neutrinos with high statistical confidence. This led to the construction of Super-Kamiokande, with ten times more water volume and PMTs than Kamiokande. Super-Kamiokande started observation in 1996. Super-Kamiokande Collaboration announced the first evidence of neutrino oscillations in 1998, consistent with the theory that the neutrino has non-zero mass. Until this, all observational evidences were consistent with neutrinos being massless, although theorists had speculated on the possibility of neutrinos having non-zero mass for many years. On November 12, 2001, several thousand photomultiplier tubes in the Super-Kamiokande detector imploded, apparently in a chain reaction as the shock wave from the concussion of each imploding tube cracked its neighbours. The detector was partially restored by redistributing the photomultiplier tubes which did not implode, and by adding protective acrylic shells that are hoped would prevent another chain reaction from recurring (SuperKamiokande-II). In July 2005, preparation began to restore the detector to its original form by reinstalling about 6,000 PMTs. It was completed in June 2006. (SuperKamiokande-III) See also | ||||||||||
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