© Courtesy Brookhaven National Laboratory.
This experiment, built deep underground in South Dakota's Homestake Gold Mine, was the first to detect neutrinos from the Sun. The storage vessel holds 100,000 gallons of dry-cleaning fluid (perchloroethylene), which turns into radioactive argon when it reacts with a neutrino. From 1967-1985, it consistently detected only one-third of the expected number of solar neutrinos, confounding lead scientist Raymond David Jr. of the Brookhaven National Laboratory. The mystery of the missing neutrinos was later resolved through results from the Sudbury Neutrino Observatory and Super Kamiokande. (Unit: 1)