Raymond Davis, Jr. (October 14, 1914 – May 31, 2006) was an American chemist, physicist, and Nobel Prize in Physics laureate.
In 1948, he joined Brookhaven National Laboratory, which was dedicated to finding peaceful uses for nuclear power.
Davis reports that he was asked "to find something interesting to work on," and dedicated his career to the study of neutrinos, particles which had been predicted to explain the process of beta decay, but whose separate existence had not been confirmed. Davis investigated the detection of neutrinos by beta decay, the process by which a neutrino brings enough energy to a nucleus to make certain stable isotopes into radioactive ones. Since the rate for this process is very low, the number of radioactive atoms created in neutrino experiments is very small, and Davis began investigating the rates of processes other than beta decay that would mimic the signal of neutrinos. Using barrels and tanks of carbon tetrachloride as detectors, Davis characterized the rate of the production of 37Argon as a function of altitude and as a function of depth underground. He deployed a detector containing chlorine atoms at the Brookhaven Reactor in 1954 and later one of the reactors at Savannah River. These experiments failed to detect a surplus of radioactive argon when the reactors were operating over when the reactors were shut down, and this was taken as the first experimental evidence that neutrinos causing the chlorine reaction, and antineutrinos produced in reactors, were distinct. Detecting neutrinos proved considerably more difficult than not detecting antineutrinos. Davis was the lead scientist behind the Homestake Experiment, the large-scale radiochemical neutrino detector which first detected evidence of neutrinos from the sun.
He shared the Nobel Prize in Physics in 2002 with Japanese physicist Masatoshi Koshiba and American Riccardo Giacconi for pioneering contributions to astrophysics, in particular for the detection of cosmic neutrinos, looking at the solar neutrino problem in the Homestake Experiment. He was 88 years old when awarded the prize.