Radiogenic heat production of rocks

Abstract

The heat produced in the radioactive decay of the unstable isotopes of uranium (238U;235U), thorium (232Th), and potassium (40K) is the largest internal heat source of the Earth. During radioactive decay, mass is converted into energy. Except for the tiny amount associated with the antineutrino and neutrinos generated in β˗-and β+ -decay or electron capture, respectively, all of this energy ends up as heat. The annual production of radiogenic heat in the Earth equals 8.6 × 1020 J, which is more than twice the global production of primary energy in the year 2000. The distribution of radiogenic isotopes in the Earth controls to a large extent the thermal regime of the Earth. Unfortunately, this distribution is known only with great uncertainty. Recently, it has become possible to detect geoneutrinos, that is, antineutrinos emitted during radioactive decay of unstable isotopes, in large detectors. With decreased size and improved accuracy of detectors together with directional resolution power, an antineutrino tomography of the Earth appears to become possible. Ideally, this would enable locating and quantifying the distribution of unstable isotopes in the Earth, thus helping to resolve a number of open questions with regard to the state and evolution of the Earth’s thermal regime.