Super-Kamiokande, Mount Kamioka, Hida, Gifu Prefecture, Japan

The Super-Kamiokande Collaboration announced the first evidence of neutrino oscillation in 1998. This was the first experimental observation supporting the theory that the neutrino has non-zero mass, a possibility that theorists had speculated about for years.
On November 12, 2001, about 6,600 of the photomultiplier tubes (costing about $3000 each ) in the Super-Kamiokande detector imploded, apparently in a chain reaction or cascade failure, as the shock wave from the concussion of each imploding tube cracked its neighbours. The detector was partially restored by redistributing the photomultiplier tubes which did not implode, and by adding protective acrylic shells that are hoped will prevent another chain reaction from recurring (Super-Kamiokande-II).
In July 2005, preparations began to restore the detector to its original form by reinstalling about 6,000 PMTs. The work was completed in June 2006, whereupon the detector was renamed Super-Kamiokande-III. This phase of the experiment collected data from October 2006 till August 2008. At that time, significant upgrades were made to the experiment's electronics. After the upgrade, the new phase of the experiment has been referred to as Super-Kamiokande-IV. SK-IV continues to run, collecting data on various natural sources of neutrinos, as well as acting as the far detector for the Tokai-to-Kamioka (T2K) long baseline neutrino oscillation experiment.