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 (geo-neutrinos) detectable by KamLAND. We found that KamLAND can be used to determine the absolute abundances of U and Th in the Earth with an accuracy sufficient for placing important constraints on Earth's accretional process and succeeding thermal history. The present observation of geo-neutrinos with KamLAND is consistent with our model prediction based on the bulk silicate Earth (BSE) composition within the uncertainty of the measurement. 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 geo-neutrino event rate on the Earth's surface indicates that geo-neutrino observation can provide key information for testing the current models for the content and distribution of U and Th in the Earth.