Picture of the Borexino detector © Borexino Collaboration Picture of the Borexino detector during the filling with liquid scintillator.

Borexino is a 300 ton liquid scintillator detector placed in the underground Laboratori Nazionali del Gran Sasso in central Italy. The unprecedented radio-purity of the scintillator was at the base of a series of spectroscopic measurements of neutrino species from the pp-cycle (pp– listed among the top 10 Physics Breakthroughs, pep, 7Be, and 8B neutrinos), a unique success of Borexino. 

Geoneutrinos, antineutrinos emitted along the decays of long-lived radioactive elements inside the Earth, are unique probes in order to determine the radiogenic heat produced in the deep Earth. Borexino, together with KamLAND in Japan, are the only two experiments being currently able to measure geoneutrinos.