The world's largest underground neutrino
observatory; a joint Japanese-American facility, it is located in the Kamioka
Mine, about 200 km north of Tokyo. It consists of a tank of ultra-pure water,
40 meters in diameter by 40 meters tall, that is monitored by thousands
of sensitive phototubes. Super-Kamiokande was badly damaged in November
2001 when a large number of the phototubes imploded in a chain reaction.
However, repairs were carried out following an inquiry into the accident
and the observatory resumed collecting data in January 2003.