Davis, Raymond, Jr.
Born Washington, USA, 14 October 1914
Died Blue Point, New York, USA, 31 May 2006
American radiochemist/physicist Raymond Davis conceived, built, and ran the first experiment to detect neutrinos from the Sun. His work provided the first direct experimental confirmation that the Sun produces energy by thermonuclear fusion of hydrogen to helium.
Davis received BS and MS degrees in physical chemistry from the University of Maryland in 1937 and 1940, respectively. In 1942, he earned a Ph.D. from Yale University also in physical chemistry. Davis served in the United States Army from 1942 to 1946, after which he worked for the Monsanto Chemical Company for 2 years. In 1948, he joined the staff at Brookhaven National Laboratory in Upton, New York, and stayed there until his retirement in 1984. In 1985, Davis joined the Department of Physics and Astronomy at the University of Pennsylvania.
Going against common wisdom in the physics community that the detection of neutrinos from reactors by Fredrick Reines and Clyde Cowan was at the limit of what could be achieved, Davis constructed a neutrino detector 1 mile underground in the Homestake Gold Mine at Lead, South Dakota. The subterranean location was chosen to reduce the background flux produced by cosmic rays.
The experiment was a radiochemical design. The 680-ton detector consisted of 100,000 gal of perchloroethylene, a common chlorine-rich dry-cleaning fluid that was available cheaply in large quantities, due to its industrial use. Neutrinos from the Sun induced the chlorine-37 atoms to convert to gaseous argon-37, which was flushed from the detector every few months and counted by its radioactive decay.
For 20 years, Davis detected only one-third of the predicted flux of solar neutrinos, leading to the “solar neutrino problem.” Since Davis’s experiment was only sensitive to the highest-energy neutrinos emitted by the Sun, some scientists believed that the problem was due to the center of the Sun being very slightly cooler than in the existing models or to experimental error. In the 1980s, Japanese physicists built a water Cherenkov-radiation detector that had been intended to see proton decay infact confirmed Davis’s result. Subsequent experiments in Italy, Russia, and Canada showed that the apparent neutrino deficit was causing neutrinos were changing “flavor” from the electron type, to which Davis’s experiment was sensitive, to μ- or τ-type neutrinos due to the Mikheyev, Smirnov, and Wolfenstein [MSW] effect. In MSW, the mass eigenstates of neutrinos are linear combinations of the flavor eigenstates, and neutrinos change flavor by interacting with matter in the Sun. This result also demonstrates that neutrinos have (a very small) mass. Davis is clearly the father of the modern field of “neutrino astrophysics.”
Davis received the Boris Pregel Prize of the New York Academy of Sciences in 1957, the Comstock Prize from the National Academy of Sciences in 1978, and the American Chemical Society Award for Nuclear Chemistry in 1979. He was elected to the National Academy of Sciences in 1982 (Astronomy). Davis received the Tom W. Bonner Prize in 1988 and the W. K. H. Panofsky Prize in 1992 from the American Physical Society, the Hale Prize from the American Astronomical Society in 1996, the Bruno Pontecorvo Prize from the Russian Academy of Sciences in 1999, the prestigious Wolf Prize in 2000, and the National Medal of Science in 2002. Finally in 2002, he shared the Nobel Prize in Physics with Masotoshi Koshiba, who developed the Japanese neutrino detector known as Kamiokande, and X-ray astronomer Riccardo Giacconi.
- Bahcall, John N. (1989). Neutrino Astrophysics. Cambridge: Cambridge University Press.Google Scholar