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Super-Kamiokande, or Super-K for
short, is a
neutrino observatory in
Japan. The observatory 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 is located
1,000 m underground in Mozumi Mine of the
Kamioka Mining and Smelting Co. in
Kamioka-cho,
Gifu,
Japan. It consists of
50,000 tons 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. The distinct pattern of this flash provides information on
the direction and flavor of the incoming neutrino.
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 the
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 observe neutrinos of cosmic origin. As a result, the detector
had become highly sensitive and had succeeded in detecting neutrinos from
a
supernova explosion 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.
Despite its success in neutrino observation, Kamiokande could not
detect the
proton decay, its first aim. Also, even higher sensitivity was in need
to observe neutrinos in high statistics confidence. This lead 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, which means
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 pressure waves
from each imploding tube cracked its neighbors. 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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