A particle detector deep under an Italian mountainside has detected direct evidence of a crucial part of the Sun's fusion process for the first time.
A team of researchers from across Europe and the United States are studying the emission of low-energy neutrinos – a little-understood particle that reacts only weakly with ordinary matter – from the core of the Sun. The reactions there fuse single protons with other elements, creating new atomic nuclei, emitting vast numbers of neutrinos in the process.
A small portion of these – about one in ten thousand – are so-called high energy, and have been detected by earlier experiments. But the low-energy majority – so numerous that about 10 billion pass through a fingernail in any given second, according to Virginia Tech Professor and project member Bruce Vogelaar – have been more difficult to detect, indistinguishable from background radiation produced by ordinary materials used in experiments.
The team of more than 100 researchers working in the Borexino Collaboration has made a number of conceptual and technological breakthroughs over the past decade allowing them to build the Italian facility, which has unprecedented levels of shielding and purity, finally allowing detection of this predicted solar radiation.
The detector itself is essentially a tank containing 350,000 gallons of organic liquid, surrounded by photosensors that capture light emitted when a neutrino passing through the space collides with an electron.
Researchers are studying the signature of neutrinos emitted by the decay of Beryllium-7, one of the critical steps in the Sun's fusion process. In a sense, this gives them a kind of time machine; the neutrinos reach Earth about 8 minutes after being emitted, while the thermal energy produced at the Sun's core takes close to 50,000 years to reach the star's surface, and then travel to Earth as sunlight, the scientists said.
The team hopes that the observations will help scientists learn more about the Sun's energy cycle, as well as help physicists gain a better understanding of the nature of neutrinos themselves.
(Photo: An internal view of the Boraxino detector. Credit: Boraxino Collaboration)
