Geoneutrinos

Geoneutrinos are electron antineutrinos produced by beta decays of radioactive isotopes within the Earth's interior. The dominant sources are uranium-238 and thorium-232 decay chains; potassium-40 also contributes antineutrinos, but its emissions are below the energy threshold for standard reactor-style detectors and thus are not readily detected by current geoneutrino experiments.

Most geoneutrinos detected by terrestrial experiments are electron antineutrinos with energy up to about 3.3 MeV from U and Th decays. They are observed via inverse beta decay on protons in large liquid scintillator detectors: antineutrino plus proton yields a positron and a neutron, with the prompt positron signal followed by a delayed neutron capture, providing a distinctive coincidence signature.

Experiments and results: The first evidence for geoneutrinos came from KamLAND in the early 2000s; Borexino has also reported measurements; ongoing and planned detectors such as SNO+, JUNO, and Jinping aim to improve precision and regional sensitivity.

These measurements help constrain Earth's radiogenic heat production and mantle composition; crustal contributions dominate the local signal, while the mantle signal is global and harder to isolate.

Limitations: Crustal heterogeneity and uncertainties in mantle distribution complicate interpretation; detection is limited by reactor backgrounds and low event rates; K-40 cannot be detected with current IBD detectors.

Impact: knowledge informs geophysical models and tests of the bulk silicate Earth model.