Following an accident last November at the Superkamiokande detector in Japan, the experiment’s spokesman, Yoji Totsuka, vowed that the detector would be rebuilt. Investigations carried out since then have shown a way to prevent such accidents happening again, and rebuilding is now under way.
Superkamiokande is a huge water Cherenkov detector in which some 11,200 photomultiplier tubes view 50,000 t of pure water 1000 m underground. It seems that shockwave propagation from a single tube imploding could have sparked off a chain reaction that destroyed the detector. The short-term solution is to encase the tubes in 13 mm acrylic plus fibre-reinforced plastic bubbles, which would contain the implosion. The recovery plan is to deploy some 47% of the full complement of tubes before the end of the year, allowing operation to resume with the K2K neutrino beam, sent from the KEK high-energy physics laboratory, early next year. Tubes will be deployed in such a way as to maximize the effectiveness of the detector for observing the K2K beam.
For the longer term, the Superkamiokande collaboration will be carrying out research and development into photomultiplier technology, studying aspects of glass shape and structure. The detector is scheduled to be fully rebuilt by 2007, in time for commissioning of a neutrino beam to be sent from the new Japan Hadron Facility.
