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Nobel Physics Prize Goes to Japanese, Two Americans - 2002-10-08

Two Americans and a Japanese researcher have won this year's Nobel Prize in physics. The Royal Swedish Academy of Sciences cites them for pioneering contributions in the detection of X-ray sources and cosmic particles.

Half the $1 million physics prize will be shared by Raymond Davis, 87, of the University of Pennsylvania and Masatoshi Koshiba, 76, of the University of Tokyo. The Swedish Academy cited them for detecting an elusive cosmic particle called a neutrino, which is produced in the nuclear fires inside stars like our sun.

The Swedish Academy says Mr. Davis became the first to do so, attempting to prove a theory about how the sun produces energy. The theory suggested that the source of that energy is the nuclear reaction changing hydrogen into helium. Since the reaction produces neutrinos, capturing them would answer the question.

But neutrino hunter Richard Hahn of the U.S. government's Brookhaven National Laboratory in New York says these particles are hard to collect because they have neither mass nor charge and rarely interact with other atoms. "The way to get around that is to make the target bigger so you have many, many more atoms available for the interaction," he said.

So in the 1950s, Mr. Davis built a big, novel neutrino trap. It was a huge tank filled with 615 tons of chlorine, some of whose atoms would change to argon if they reacted with a neutrino. The trap was buried deep underground to block other types of cosmic rays from interfering with the reactions.

Over a 30-year period, Mr. Hahn says Raymond Davis collected 2,000 neutrinos from the sun in the form of argon atoms converted from chlorine.

"He saw them, so that was great in the general sense that there's proof that nuclear energy is what powers the sun and what sustains life on the Earth," he said.

Japanese physicist Masatoshi Koshiba confirmed Mr. Davis' results with an enormous tank deep inside a mine, but with a different liquid. He used water. The reaction of neutrinos with water atoms released electrons that produced tiny flashes observed by magnification. Unlike Mr. Davis' experiments, Mr. Koshiba's were sensitive to direction, thereby proving for the first time that neutrinos came from the sun.

The other half of the Nobel physics prize goes to Riccardo Giacconi, a 71-year-old Italian-born scientist at Associated Universities, Incorporated in Washington.

He was the first to detect sources of X-rays outside the solar system and prove that the universe contains background X-ray radiation, which the atmosphere absorbs. The Swedish Academy of Sciences says his unexpected discoveries gave an impetus to the development of X-ray astronomy and ultimately the X-ray detecting satellites now orbiting Earth.

The Nobel Prize citation says the three scientists have changed the way we look at the universe by using the continuous shift of cosmic particles to increase our knowledge of the sun, stars, and other celestial phenomena.