Revealing the Thermal History of the Earth through Geoneutrino Measurement with KamLAND

Kawada Nanami

doi:10.11316/butsuri.79.3_117

<p>The decay of radioactive isotopes, uranium, thorium and potassium, in the Earth’s interior generates a significant amount of radiogenic heat and contributes to the Earth’s heat budget. The abundance of these elements is a key parameter in revealing the geophysical activity of the planet. Geoneutrinos produced by these isotopes are a unique probe of the composition and hence the amount of the radiogenic heat in the Earth. KamLAND has been observing geoneutrinos from ²³⁸U and ²³²Th with a 1 kilotonne liquid scintillator for more than 20 years. The low-reactor period since 2011 allowed a spectroscopic measurement of geoneutrinos from ²³⁸U and ²³²Th by reducing the most serious background, the reactor neutrino. The number of geoneutrino signals is estimated to be 116.6^+41.0_-38.5, 57.5^+24.5_-24.1 and 173.7^+29.2_-27.7 from ²³⁸U, ²³²Th and ²³⁸U+²³²Th, respectively. These correspond to geoneutrino fluxes of 14.7^+5.2_-4.8, 23.9^+10.2_-10.0 and 32.1^+5.8_-5.3×10⁵ cm^-2 s^-1, respectively. The null-signal hypothesis is rejected at the 8.5σ confidence level. This study provides the first constraint on the radiogenic heat contribution of ²³⁸U and ²³²Th individually, which is consistent with geochemical predictions based on the compositional analysis of chondrite meteorites.</p>

Revealing the Thermal History of the Earth through Geoneutrino Measurement with KamLAND

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