Solar neutrinos

Previous discovery of antineutrinos made the existence of neutrinos certain, but there was no experimental proof yet. To remedy, Reines set up a tank containing 100,000 gallons of tetrachloryethylene in a mine in South Dakota, left it exposed for several months and came back with definitive proof of argon (and helium) from chlorine reacting with neutrinos.
 Frederick Reines United States 1968 Solar neutrinos

Previous discovery of antineutrinos made the existence of neutrinos certain, but there was no experimental proof yet. To remedy, Reines set up a tank containing 100,000 gallons of tetrachloryethylene in a mine in South Dakota, left it exposed for several months and came back with definitive proof of argon (and helium) from chlorine reacting with neutrinos.