In a major setback for neutrino research, an accident during repairs to the Super-Kamiokande neutrino detector in central Japan has knocked the detector out of commission for the foreseeable future.
Buried a kilometer underground in a mine to screen out background radiation, Super-Kamiokande, a $100 million facility, is a 39-meter-by-41-meter tank of pure water lined with 11,146 photomultiplier tubes. The tubes watch for a characteristic glow, known as Cerenkov radiation, from the statistically rare interaction of ephemeral neutrinos and atomic particles in the water. In 1998, the detector provided researchers with the first convincing evidence that neutrinos have mass (ScienceNOW, 5 June 1998).
The tank had been emptied in August to replace 100 burned-out tubes and was being refilled on Monday when more than half of the 11,146 tubes suddenly shattered in an apparent chain reaction. Yoji Totsuka, director of the University of Tokyo's Institute for Cosmic Ray Research (ICRR), which heads an international collaboration of 120 physicists from 23 institutions operating Super-Kamiokande, says he has no idea what caused the accident or how soon the facility can be put back on line.
The ICRR will set up a team to determine the cause of the accident and what to do next. Totsuka wouldn't comment on the cost of repairing the facility until more is known. But a Super-Kamiokande source puts the cost of replacing the tubes in the neighborhood of $10 million. Totsuka vows to get the facility back on line. "All the researchers here are determined to get back to the forefront of neutrino research," he says.