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geoneutrino
Geoneutrino is an electron antineutrino emitted in of a radionuclide naturally occurring in the Earth. Neutrinos, the lightest of the known subatomic particles, lack measurable electromagnetic properties and interact only via the weak nuclear force. Matter is virtually transparent to neutrinos and consequently they travel, unimpeded, at near light speed through the Earth from their point of emission. Collectively, geoneutrinos carry integrated information about the abundances of their radioactive sources inside the Earth. A major objective of the emerging field of neutrino geophysics involves extracting geologically useful information (e.g., abundances of individual geoneutrino-producing elements and their spatial distribution in Earth’s interior) from geoneutrino measurements.
Most geoneutrinos originate from decay-branches of 40K, 232Th and 238U. Together these decay chains account for more than 99% of the present-day radiogenic heat generated inside the Earth. Only geoneutrinos from 232Th and 238U decay chains are detectable by the inverse beta-decay mechanism because these have energies above the corresponding threshold (1.8 MeV). In neutrino experiments, large underground liquid scintillator detectors record the flashes of light generated from this interaction. geoneutrino measurements at two sites, as reported by the KamLAND and Borexino collaborations, have begun to place constraints on the amount of radiogenic heating in the Earth's interior. A third detector (SNO+) is expected to start collecting data in 2015. A number of future geoneutrino detectors are being planned.
==History==
Neutrinos were hypothesized in 1930 by Wolfgang Pauli. The first detection of antineutrinos generated in a nuclear reactor was confirmed in 1956. The idea of studying geologically produced neutrinos to infer Earth’s composition has been around since at least mid-1960s. In a 1984 landmark paper Krauss, Glashow & Schramm presented calculations of the predicted geoneutrino flux and discussed the possibilities for detection. First detection of geoneutrinos was reported in 2005 by the KamLAND experiment at the Kamioka Observatory in Japan. In 2010 the Borexino experiment at the Gran Sasso National Laboratory in Italy released their geoneutrino measurement. Updated results from KamLAND were published in 2011.
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