The Super Kamiokande is a testing facility that was built 1,000 meters underground, within the Kamioka mine in the town of Kamioka-cho, Gifu Prefecture, in order to study the riddle of the elementary particles called neutrinos. The overall facility forms a vast cylindrical tank measuring 39 meters in diameter and 41 meters in height, and is filled with 50,000 tons of pure water. There are 11,300 optical sensors in the form of 20-inch photomultiplier tubes made by Hamamatsu Photonics attached to the walls and the bottom of the tank. As the neutrinos pass through the pure water in the tank at high speed, once in a great while they react with the water molecules and emit light. This very faint light is picked up by the photomultiplier tubes, which detect the amount of energy that the neutrinos have and the direction from which they came.

PET (positron emission tomography) is an imaging diagnostic tool used in medical care that can detect the state of complex functions active within the human body. PET is drawing keen interest from researchers and people in the medical profession worldwide as a means of clarifying the complex functions of the brain and other living organisms, and also as a way to detect cancer and other illnesses at an early stage. With PET, gamma rays given off from the body in response to chemicals that have been injected, and these rays are detected by the PET device and presented as images. Photomultiplier tubes are used in the detection of these gamma rays.

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