C&EN: TODAY'S HEADLINES - NOBEL LIGHT SHINES ON ASTROPHYSICS

MITCH JACOBY

Far out in the cosmos, astrophysical events give rise to energetic particles and forms of light that radiate through the heavens and sometimes right through planet Earth. For advancing understanding of these cosmic processes, two physicists and a physical chemist have been awarded the 2002 Nobel Prize in Physics.

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Davis
BROOKHAVEN PHOTO

Raymond Davis Jr., 87, a research professor of physics at the University of Pennsylvania and a collaborator in chemistry research at Brookhaven National Laboratory, and Masatoshi Koshiba, 76, professor emeritus at the University of Tokyo’s International Center for Elementary Particle Physics, will share half of the $1 million prize for detecting cosmic neutrinos and for other advances in astrophysics. The other half of the prize has been awarded to Riccardo Giacconi, 71, president of Associated Universities Inc., in Washington, D.C., for his contributions that led to the discovery of cosmic X-ray sources.

Nearly massless neutrinos were postulated in 1930 by Wolfgang Pauli to explain the energy spectrum of electrons emitted in -decay nuclear reactions. But it wasn’t until the 1950s that 1995 Physics Nobel Laureate Frederick Reines detected the elusive particles in nuclear reactor studies. Davis sought to detect neutrinos that were released in nuclear reactions on the sun (and traveled to Earth) as a way of confirming that the sun’s energy comes from fusion reactions that form helium from hydrogen. But neutrinos are difficult to detect because they hardly interact with matter. For example, scientists calculate that every second, trillions of neutrinos pass unnoticed through our bodies and through Earth.

So in the 1960s, Davis designed an experiment in which a tank filled with more than 600 tons of inexpensive perchloroethylene, a dry-cleaning solvent, served as a neutrino detector. The expectation was that neutrinos would interact with chlorine atoms in the solvent, converting a minuscule—but detectable—number of chlorine atoms to argon atoms. To Davis’ credit, the experiment, which ran for some 30 years in a gold mine in Lead, S.D., yielded about 10 neutrinos (that is, 10 argon atoms were detected) per month.

Koshiba’s investigations confirmed Davis’ findings on solar neutrinos and led to the detection of 12 neutrinos out of some 10¹⁶ that passed through a detector in Japan following a supernova explosion in 1987. More recently, Koshiba proved that neutrinos can oscillate from one form to another.

Meanwhile, Giacconi’s work on satellite-borne X-ray detectors and telescopes provided the first glimpse of X-rays from sources outside of the solar system and relatively sharp images of the universe at X-ray wavelengths.