__      __
 ___   _ _     _ _   ___ ___ ___     _ _     _ ___    ___ ___\ \    / /___
| | | / | \   / | \ | | |_  |_  |   / | \   / |  _|  |_  |_  |\ \  / /|_  |
|_  |/ / \ \ / / \ \|_  |  _|_| |_ / / \ \ / /| . |    | |_  | > >< <   | |
  |_|_/   \_|_/   \_| |_|___|_____|_/   \_|_/ |___|    |_|___|/ /  \ \  |_|
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     whereof one cannot speak thereof one must be silent.
The neutrino, a product of certain nuclear decay reactions, is maddeningly hard to detect, even from the nearby Sun. In the early 1950s, at Brookhaven National Laboratory in Upton, NY, Raymond Davis developed a system for capturing the radioactive argon atoms produced when neutrinos collide with molecules containing chlorine and carbon. He filled a tank in the Homestake Gold Mine in South Dakota with over 600 tons of the dry-cleaning fluid perchloroethylene (C2Cl4), bubbling helium through it to remove the argon produced by neutrinos. The amount of argon then gave a measure of the number of neutrinos that hit the tank.