Neutrino geophysics with KamLAND and future prospects

The Kamioka liquid scintillator anti-neutrino detector (KamLAND) is a low-energy and low-background neutrino detector which could be a useful probe for determining the U and Th abundances of the Earth. We constructed a model of the Earth in order to evaluate the rate of geologically produced anti-neutrinos (geoneutrinos) detectable by KamLAND. We found that KamLAND can be used to determine the absolute abundances of U and Th in the Earth with accuracy sufficient for placing important constraints on Earthʹs accretion and succeeding thermal history. Within the uncertainty of the measurement, the present observation of geoneutrinos with KamLAND is consistent with our model prediction based on the bulk silicate Earth (BSE) composition. If a neutrino detector were to be built in Hawaii, where effects of the continental crust would be negligible, it could be used to estimate the U and Th content in the lower mantle and the core. Our calculation of the geoneutrino event rate on the Earthʹs surface indicates that geoneutrino observation can provide key information for testing the current models of the U and Th content and distribution in the Earth.