A typical neutrino event at Super K ()

Super-Kamiokande (神岡), or Super-K for short, is a neutrino observatory in Japan.
The experiment was designed to study solar neutrinos, study atmospheric neutrinos, search for proton decay, and detect neutrinos from a supernova anywhere in our galaxy. Super-K announced the first evidence of neutrino oscillations in 1998.

Super-K consists of a large amount of pure water surrounded by about 11000 photomultiplier tubes. The cylindrical structure is 40 m tall and 40 m across. A neutrino interaction with the electrons or nuclei of water can produce a particle that move faster than the speed of light in water (although of course slower than the speed of light in vacuum). This creates a flash of light due to Cherenkov radiation which is the optical equivalent to a sonic boom. This flash provides distinctive patterns of light which are recorded and which provides information on the direction and flavor of the incoming neutrino.


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 investigate the stability of matter, one of the most fundamental questions of elementary particle physics.

Kamioka Underground Observatory was located 1,000 m underground of Mozumi Mine of the Kamioka Mining and Smelting Co. located in Kamioka-cho, Gifu, Japan. The detector (KAMIOKANDE: 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. The PMTs collect the pale blue light called cerenkov light which is emitted by high-velocity charged particles travelling as fast as light in the water.

An image inside the detector where technicians maintain the photomultiplier tubes in a boat on top of the pure water. Water is used because of its excellent cost/refractive index ratio ()

An upgrade of the detector was started in 1985 to observe elementary particles called neutrinos of cosmic origin. As a result, the detector had become hightly sensitive and had succeeded in detecting neutrinos from a supernova explosion which occurred in the Large Magellanic Cloud in Febrary 1987.
Solar neutrinos were observed in 1988 adding to the advancements in neutrino astronomy and neutrino astrophysics. Until mass was confirmed in 1998, all observational evidence was consistent with neutrinos being massless, although theorists had speculated on the possibility of neutrinos having non-zero mass for many years.

A schematic diagram of the detector ()

On November 12, 2001, several thousand photomultiplier tubes in the Super-Kamiokande detector imploded, apparently in a chain reaction as the pressure waves from each imploding tube cracked its neighbours.
The detector has been partially restored with about 5000 photomultiplier tubes with protective shells that will prevent the chain reaction from recurring.

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