Raymond Davis

Born October 14, 1914, in Washington, DC; died of complications of Alzheimer's disease, May 31, 2006, in Blue Point, NY. Physicist. Raymond Davis Jr. won the 2002 Nobel Prize in physics for detecting neutrinos from the sun, the final proof that the sun is powered by nuclear fusion. When he began his experiments in 1961, Davis was one of the few scientists who thought that solar neutrinos could ever be detected. Other scientists scoffed, pointing out that neutrinos hardly ever interacted with other matter. But through tenacity, Davis proved them wrong. His work led to a new field, neutrinoastronomy. "Ray was the most optimistic person you could ever encounter," Kenneth Lande, a physicist at the University of Pennsylvania and former colleague of Davis, told Kenneth Chang of the New York Times. "For Ray, this was a challenge. The greater the challenge, the more fun it was to attack it."

Davis was born in Washington, D.C., in 1914, the son of a self-educated inventor who worked for the National Bureau of Standards. Davis studied chemistry at the University of Maryland, where he earned bachelor's and master's degrees, and Yale University, where he earned his doctorate in 1942. Between degrees, he worked for a year for the Dow Chemical Company in Midland, Michigan. In 1942, he joined the Army Air Forces and worked as an observer of chemical weapon tests at the Dugway Proving Ground in Utah. After leaving the Army in 1946, he worked for the Monsanto Chemical Company in Miamisburg, Ohio, studying radioactive isotopes. In 1948, he joined the Brookhaven National Laboratory on Long Island, New York, where he spent the rest of his career. He also met his wife, biologist Anna Torrey, there.

Brookhaven gave Davis wide latitude to choose just about any research project that appealed to him. He chose to study neutrinos, tiny and elusive atomic particles. Neutrinos have little or no mass, travel at almost the speed of light, and hardly ever interact with other matter. But they proved to be very important to proving why the sun burns. At the time, researchers studying the sun were theorizing that it was powered by nuclear energy. Astrophysicists had concluded that hydrogen atoms fuse inside the sun to create helium atoms, releasing vast amounts of energy. They also concluded that for each helium atom created, two neutrinos would be released. But most researchers thought the neutrinos could never be detected, because almost all of them would pass straight through the Earth, and only one in a trillion would actually strike the planet.

Davis thought the scientists were wrong to think neutrinos undetectable. He noted that an Italian physicist, Bruno Pontecorvo, had calculated that if a neutrino hit a chlorine atom, the chlorine atom would be transformed into a radioactive argon atom, which is detectable. So Davis put together an experiment, placing a big tank that held a dry-cleaning fluid containing chlorine in a limestone mine in Ohio in 1961. The idea was that putting the tank underground would block out cosmic rays, but the mine was not deep enough, and the rays drowned out the neutrinos' signal. So, later in the 1960s, Davis installed another tank in a gold mine almost a mile underground in South Dakota. At first, that experiment did not detect neutrinos either. Other scientists thought he should give up. So, to prove that neutrino detection through chlorine and argon was possible, Davis synthesized 100 argon atoms, released them into the tanks, then extracted them back out.

Once Davis and his team got better at detecting argon in the mid-1970s, they started detecting neutrinos. In 30 years, they detected 2,000—the final proof that nuclear fusion occurs in the sun. Brookhaven administered the experiment until Davis retired in 1984. Then it was transferred to the University of Pennsylvania, which Davis joined as a research professor. The experiment continued until the mine closed in the late 1990s. In 2002, the Swedish Royal Academy of Sciences awarded Davis the Nobel Prize in physics for his discovery, describing his feat as more difficult than finding a few specific grains of sand in the Sahara Desert. He shared the prize with Masatoshi Koshiba of the University of Tokyo and Ricardo Giacconi of Johns Hopkins University, who had confirmed his findings.

Occasionally, Davis took a break from neutrinos to work on other projects. He examined meteorites to look at their radioactive isotopes. His most successful work in that field involved what is known as the Lost City meteorite, which was photographed several times as it plunged to Earth, allowing scientists to determine its orbit. By looking, again, at radioactive argon atoms, Davis and his colleagues figured out how intense cosmic rays are in the inner solar system. From 1971 to 1973, as part of the National Air and Space Administration's Lunar Sample Return Board, Davis examined moon rocks that the Apollo space crews brought back to Earth. He was even quarantined for two weeks, to make sure there were no diseases in the moon material, when a glove box the researchers were using leaked.

Davis suffered from Alzheimer's disease for four years before dying of complications of the disease on May 31, 2006, at his home in Blue Point, New York. He was 91. He is survived by his wife, Anna; his sons Andrew, Roger, and Alan; his daughters Martha and Nancy; and eleven grandchildren.

Sources:

Los Angeles Times, June 3, 2006, p. B14; New York Times, June 2, 2006, p. C10; June 3, 2006, p. A2; Times (London), June 29, 2006, p. 64.