The Sudbury Neutrino Observatory：萨德伯里中微子天文台.pdf

40 SCIENTIFIC AMERICAN The Sudbury Neutrino Observatory has solved a 30-year-old mystery by showing that neutrinos from the sun change species en route to the earth By Arthur B. McDonald, Joshua R. Klein and David Solving the Building a detector the size of a 10-story building two kilometers underground is a strange way to study solar phenomena. Yet that has turned out to be the key to unlocking a decades-old puzzle about the physical processes occurring inside the sun. Eng- lish physicist Arthur Eddington suggested as early as 1920 that nuclear fusion powered the sun, but efforts to confirm critical details of this idea in the 1960s ran into a stumbling block: experiments designed to de- tect a distinctive by-product of solar nuclear fusion re- actions — ghostly particles called neutrinos — observed only a fraction of the expected number of them. It was not until last year, with the results from the under- ground Sudbury Neutrino Observatory (SNO) in COPYRIGHT 2003 SCIENTIFIC AMERICAN, INC. So l ar N eut rino Problem COPYRIGHT 2003 SCIENTIFIC AMERICAN, INC. Ontario, that physicists resolved this conundrum and thereby fully con?rmed Eddington’s proposal. Like all underground experiments designed to study the sun, SNO’s primary goal is to detect neutrinos, which are pro- duced in great numbers in the solar core. But unlike most of the other experiments built over th