US and Japan Plan to Create Cross‐Country Neutrino Beams

Deep inside the Kamioka zinc mine, in the mountains west of Tokyo, the just‐completed Super Kamiokande proton‐decay and neutrino detector is now being filled with 50 000 tons of highly purified water. (Fifty thousand tons is the displacement of a large battleship.) Super Kamiokande is a Japan‐US collaboration. In a few months this newest, and largest by far, of the water‐Cerenkov detectors will be recording neutrinos from the Sun and from collisions of cosmic rays in the atmosphere. It will also be keeping its 11 200 photomultiplier eyes peeled for neutrino bursts from distant supernova explosions and for evidence that one of the detector's $1034$ nucleons has decayed. (See the photograph on this page).