BROOKHAVEN NATIONAL LABORATORY / SCIENCE PHOTO LIBRARY BROOKHAVEN NATIONAL LABORATORY / SCIENCE PHOTO LIBRARY
View of the giant tank of dry-cleaning fluid which forms the Homestake detector for solar neutrinos, seen shortly after construction in the Homestake Gold Mine, South Dakota, in 1967. The detector is the work of physicist Raymond Davis Jr. Still in operation in 1993, it has found only about one third of the neutrinos predicted by the standard theory of nuclear interactions in the Sun. The tank contains perchlorethylene. Neutrinos occasionally interact with a chlorine-37 nucleus in this fluid and transform it into an argon-37 nucleus; the argon decays reveal how many such interactions have occurred.
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