http://www.particlephysics.ac.uk/news/picture-of-the-week/picture-archive/one-small-part-of-super-kamiokande.html Phototube Last week's picture showed 9000 phototubes in the Super-Kamiokande detector, 1000 metres underground in a mine in Kamioka in Japan. The detector contains 50,000 tonnes of water, and the phototubes, which line the walls, watch for flashes of light (Cherenkov radiation) caused by the interactions of the elusive particles called neutrinos. Here we see just one of the 50-cm diameter phototubes, with members* of the team from the University of Hawaii who participate in the experiment together with scientists from a total of 23 institutions in Japan and the US. http://www.particlephysics.ac.uk/news/picture-of-the-week/picture-archive/super-kamiokande--9000-neutrino-eyes.html 3281 feet underground in a mine near Kamioka, Japan, a huge tank of ultra-pure water, 138 feet high and 128 feet in diameter, watches for tiny, ultra dim flashes of light caused by neutrinos hitting the molecules of water. The flashes are so dim that it takes over 11,000 "eyes", or photomultiplier tubes to see them.

A neutrino is the smallest atomic particle known to nuclear physics. It is so small, in fact, that it tends to pass through the empty space of atoms and molecules without stopping. It does this so well that it can pass through the entire earth without slowing down or hitting anything.

But, now and then, on very rare occasions, one of them will hit something, and when it does, it makes a tiny spark of light.

So, nuclear physicists decided to put some light sensors into water so pure that it has perfect clarity, and to put this water so far under the earth that no other types of radiation can possibly reach it. Then, if there is a tiny spark of light, they know that they have just witnessed the collision of a neutrino with an atom.

The walls, ceiling and floor of the tank - which is the major part of a detector called Super-Kamiokande - are covered at regular intervals by 11,146 light-sensitive phototubes, each about 50 cm in diameter. These pick up light (Cherenkov radiation) emitted as the energetic charged particles produced in the neutrino interactions travel through the water. This picture shows about 9000 of the tubes - the small bright spots - on the walls and ceiling of the tank, before it was filled with water. Super-Kamiokande detects neutrinos emitted in nuclear interactions in the Sun, and also in the interactions of cosmic-ray particles in the atmosphere. Measurements of these "atmospheric neutrinos" suggest that neutrinos may "oscillate" - change from one type to another - which they can do only if they have some mass, although this mass must be very, very small. http://www.particlephysics.ac.uk/news/picture-of-the-week/picture-archive/birthplace-of-solar-neutrino-physics.html birthplace_solar_nutrino.jpg This photo from 1966 shows the construction of the tank used in the solar neutrino experiment in the Homestake gold mine. The tank, 20 feet in diameter and 48 feet long, held 100,000 gallons of perchloroethylene and was located 4,900 feet below ground surface. The experiment found fewer neutrinos than expected, and hence gave rise to the famous "solar neutrino problem" - which only recently appears to have been solved. The experiment was turned off in 2001, when the mine closed, but the company that owns the mine continued to pump water from the mine while a group of scientists negotiated hard to establish a world-class National Underground Science and Engineering Laboratory - NUSEL - in the mine. Last week - despite lobbying by Nobel prize winners - on 10 June 2003, the company stopped pumping water, and the future of this important scientific seems doomed. http://physicsworld.com/cws/article/news/3229 diagram.jpg Jun 5, 1998 Super-Kamiokande finds neutrino mass A team of Japanese and American physicists claim to have found evidence that neutrinos have mass. Experiments at the Super-Kamiokande detector in Japan suggest a neutrino mass of 0.07 electron volts - less than one millionth of the mass of the electron. The results, presented today at the Neutrino 98 conference in Japan, have immense significance for particle physics and cosmology. However, recent budget cuts could lead to the experiment, which currently runs all year round, being closed down for two months of the year. The Super-Kamiokande collaboration say that such a closure would have a "devastating impact" on research at the facility. Neutrinos come in three types - electron neutrinos, muon neutrinos and tau neutrinos - and only interact very weakly with matter, which makes them extremely difficult to detect. Neutrino detectors have to be built underground to isolate them from cosmic rays. Even then natural radioactivity from the detector itself can mimic a neutrino interaction, so the detector must be made from ultrapure materials and isolated from its surroundings. The Super-Kamiokande experiment consists of 50, 000 tons of ultrapure water in a tank 1000 metres below ground in central Japan. It can detect both electron neutrinos and muon neutrinos - but not tau neutrinos - from the faint flashes of light given off when they interact with electrons in the water molecules. Neutrinos. According to the Standard Model of particle physics neutrinos have zero mass. However, experiments to measure neutrinos from the Sun and atmospheric neutrinos - produced when cosmic-rays interact with nuclei in the Earth's atmosphere - detect fewer of these elusive particles than predicted. One possibility is that electron neutrinos can 'oscillate' into muon and tau neutrinos, and vice versa. However, this is only possible if neutrinos have mass. A non-zero neutrino mass could also explain some of the 'missing mass' in the universe. Super-KamiokandeSuper-Kamiokande has found evidence for oscillations, and hence mass, in atmospheric neutrinos. Data from Super-Kamiokande show that more muon neutrinos enter the detector from above than below. Neutrinos entering from above would have travelled only tens of kilometres through the atmosphere, while those from below would have also had to travel through the Earth. The Super-Kamiokande team claim that the muon neutrinos oscillate into tau neutrinos - or, possibly, a new type of 'sterile' neutrino - on their journey through the Earth. "One only gets such great data once or twice in a professional lifetime, maybe never, " says John Learned of the University of Hawaii, one of the Super-Kamiokande team. However, the future success of Super-Kamiokande could be compromised by the recent financial turmoil in Japan. The government cut the experiment's budget by 15 per cent this year, and another 15 per cent is scheduled for next year. If imposed this second cut will force the laboratory to close down for part of the year. Physicists at Neutrino 98 are appealing for extra funding to ensure continuous operation for the experiment. "Budget cuts ... jeopardise the strength of the international collaboration and could result in the loss of important observations, such as a rare supernova event, " they say. http://en.wikipedia.org/wiki/Image:Super-k.jpg FillingUp.jpg http://ale.physics.sunysb.edu/superk/detector/ sk.gif sk-canonical.gif Super-Kamiokande (aslo SuperK or SK) is located in the Japanese alps near the town of Kamioka (see map to the right, click for all of Japan) in Gifu-prefecture. This is about half way between the city of Toyama, to the north on the sea, and the city of Takayama to the south. Takayama is also the location of Neutrino `98, where SuperK first announced evidence for neutrino mass. The detector is also about 250 kilometers west of KEK in Tsukuba Science City where the front detectors and accellerator of the K2K long baseline experiment reside The detector is located 1 kilometer below Mt. Ikenoyama inside the Kamioka Mining and Smelting Company's zinc mine (see inset of figure to the left). The detector is reached by driving Toyota Landcruisers about a kilometer through a level drift in Japans fastest mine road (20kph). Just down a side drift from this main one is the decommissioned predecessor to SuperK, Kamiokande, which is also the sight of the new KamLAND experiment. It is a very busy mine. The detector itself is a water Cherenkov detector. It is a 40 meter tall and 40 meter in diameter stainless steel cylinder containing 50,000 metric tons of ultra pure water, some of the purest in the world. It consists of three optically separated and concetric cylindrical regions. From inner most to outer most (see figure on right) they are: The inner detector (ID) is 36 m high and 34 m in diameter and is the main sensitive region. It is viewed by 11146 50 cm inward facing Hamamatsu photomultiplier tubes (PMTs) and surrounds 32.5 ktons of water. The dead space is a 0.5 m thick cylindrical shell which contains the stainless steel support structure as well as water. It is optically separated from the ID by opaque black plastic and from the OD (see next) by black polyethylene bonded to reflective DuPont Tyvek. The outer detector (OD) is a 2.0 m to 2.2 m thick cylindrical shell which surrounds the entire ID. It is viewed 1885 20 cm outward facing PMTs with 60 cm by 60 cm wavelength shifter plates and is lined with reflective Tyvec to increase the number of photons detected. http://www.spaceref.com/news/viewnews.html?id=411 Monday, November 19, 2001 - Comments Accident A large neutrino observatory in Japan has been heavily damaged by a freak accident. The Super-Kamiokande Observatory was designed to detect neutrinos by using a vast array of photomultiplier tubes. These sensors detect the telltale flashes of light that neutrinos produce as they pass through the observatory's immense tank of ultrapure water. On 12 November 2001, one of the observatory's 11,200 photomultiplier tubes failed causing a cascade or chain reaction wherein many of the other tubes were destroyed as well. The observatory is now inoperable as a result. The observatory was quite prolific and has yielded new insights in neutrino behavior.