In certain nuclear reactions (such as when protons combine to form helium nuclei) elusive particles called neutrinos are created. Raymond Davies wanted to detect neutrinos in radiation from space to confirm the theory that this kind of nuclear reaction is the source of the sun's energy. Beginning in the 1960s, he placed a large tank containing a chlorine-rich liquid inside a mine. In rare cases, a neutrino interacted with a chlorine atom to form an argon atom. By counting these argon atoms, neutrinos from space could be detected.