About the Detector 1

The KamLAND detector is located in a cylindrical cavern of 20-meter diameter and 20-meter deep in the Kamioka Mine (Kamioka Town, Hida City, Gifu Prefecture) with 1000-meter’s rock overburden. Why the detector is located in such a deep underground ? Because it must be shielded against cosmic rays showering.on the earth,that occur backgrounds overwhelming tiny neutrino signals. When a high energy proton from outer space collide with a nucleus in the earth’s atmosphere, high energy particles such as muons are produced and reach the earth’s surface as cosmic rays. The average intensity of cosmic rays is about one per cm^2 per minute. Cosmic rays shower down on the Earth’s surface everywhere and everytime. If you hold out your hand palm up to the sky, one cosmic ray is passing through your palm almost every second,however, such budget is completely harmless to humans. If a neutrino detector of 13-meter diameter like KamLAND is located on the ground, about 100 thousands cosmic rays come into the detector every second and overwhelm about two neutrino signals per day. The detector shielded with dirt and rock in where 1000 meter under the ground reduces the intensity of cosmic rays 100 thousands times lower than the ground.

By the way, in this cavern with KamLAND, an experimental device “Kamiokande” had been operated by University of Tokyo until 1997. From Kamiokande, a lot of discoveries, such as the detection of supernova neutrinos in 1987 and the detection of solar neutrinos,were reported. In 2002, Masatoshi Koshiba, Professor Emeritus of the University of Tokyo, won the Nobel Prize in Physics for these accomplishments. Kamiokande was transferred from the University of Tokyo to the Research Center for Neutrino science, Tohoku University, and Professor Atsuto Suzuki led international collaboration into building a more sensitive neutrino detector in the site. This is the KamLAND detector.      Next

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