🔬 Borexino

Borexino was a deep underground particle physics experiment to study low energy (sub-MeV) solar neutrinos. The detector was the world's most radio-pure liquid scintillator calorimeter and was protected by 3,800 meters of water-equivalent depth. The scintillator was pseudocumene and PPO which was held in place by a thin nylon sphere. It was placed within a stainless steel sphere which held the photomultiplier tubes (PMTs) used as signal detectors and was shielded by a water tank to protect it against external radiation. Outward pointing PMT's look for any outward facing light flashes to tag incoming cosmic muons that manage to penetrate the overburden of the mountain above. Neutrino energy could be determined through the number of photoelectrons measured in the PMT's, while the position could be determined by extrapolating the difference in arrival times of photons at PMT's throughout the chamber.