Abstract
Radioactive isotopes inside the Earth produce geo‐neutrinos through beta decays. Geo‐neutrinos could be direct probes to investigate the interior of the Earth as a supplement to the current geophysical survey that mainly relies on an indirect seismic approach. After the Kamioka liquid scintillator antineutrino detector (KamLAND) reported the first indication of geo‐neutrinos in 2005, we have accumulated data for a total of 2,135 days of live‐time and achieved a lower background level by purifying liquid scintillator. The number of obtained geo‐neutrino events is 106−28+29 corresponding to an electron antineutrino flux of 4.3−1.1+1.2×106 cm−2 s−1 from 238U and 232Th series at the Earth's surface. The null hypothesis for the existence of geo‐neutrinos is excluded at the 99.997% confidence level. We combined this precise result with that of the Borexino experiment to obtain 20.0−8.6+8.8 TW as a contribution of 238U and 232Th to the Earth heat flow.
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