Geoneutrino

Geoneutrinos are electron antineutrinos produced by beta decays of long-lived radioactive isotopes within the Earth, primarily uranium-238, thorium-232, and to a lesser extent potassium-40. These antineutrinos can pass through matter with negligible interaction, providing a direct probe of radioactive processes that contribute to Earth's heat.

Geoneutrino production originates in the radioactive decay chains of U-238 and Th-232 and, to a smaller degree, K-40, distributed throughout the crust and mantle. The antineutrino spectrum extends to a few MeV, with detectable signals mainly from the U and Th decay chains. The exact crustal versus mantle contributions and the total radiogenic heat depend on geological models and remain a source of uncertainty.

Detection relies on inverse beta decay in large liquid scintillator detectors. The reaction has a threshold of 1.806 MeV, producing a distinctive coincidence signal from a positron and a neutron. Because interaction probabilities are small, geoneutrino event rates are low, and measurements must contend with backgrounds from reactor antineutrinos and cosmogenic sources. Potassium-40 antineutrinos are generally below the detection threshold of standard detectors, making most measurements sensitive to U and Th sources.

Experiments such as KamLAND (Japan) and Borexino (Italy) have achieved the first detections and subsequent measurements of geoneutrinos, with ongoing data from SNO+ and future projects like JUNO expected to improve precision. Geoneutrino research constrains the Earth’s radiogenic heat budget and informs models of mantle composition and planetary evolution.