Technician holding a 50cm photomultiplier tube used in the search for proton decay at Tokyo University's Kamiokande experiment. Hundreds of such tubes line a tank containing 9000 tonnes of water some 1000 meters underground in a zinc mine in Japan. The experiment was designed to look for decaying protons. If a proton decays, the charged particles it generates move through the water faster than light, and generate blue Cerenkov radiation. It is this that the photomultipliers detect. Computer analysis then determines whether the event was a decay, or a collision with a solar neutrino. Photographed in 1985 in Japan.