Published by Communications and Public Affairs (519) 824-4120, Ext. 56982 or 53338
September 08, 2003
‘Pinch of salt’ helps SNO, U of G scientists further explain mysteries of the sun
A common commodity that people sprinkle on their food every day has helped scientists at the Sudbury Neutrino Observatory (SNO), including University of Guelph physicists, further explain the mystery of missing solar neutrinos.
Table salt was the main ingredient in new measurements released Sunday by SNO researchers at a scientific conference in Seattle, Wash. The measurements collected at SNO – a neutrino telescope the size of a 10-storey building and located two kilometres underground in a mine near Sudbury – verify earlier findings about what happens to electron neutrinos generated by the sun. They confirm that two-thirds of the electron-type neutrinos produced by nuclear reactions in the core of the sun change to other types of neutrinos – muon and tau neutrinos – before reaching Earth. The new measurements also go much further in establishing the properties of neutrinos that cause them to change.
“We are much more confident now of the data released in 2001 and 2002,” said U of G physics professor Jimmy Law, one of SNO’s scientists. “Any uncertainty has been mostly squeezed out.” Law and other U of G scientists helped design and construct the sophisticated instruments at SNO, which was completed in 1998 and relies on heavy water to detect neutrinos from the sun and other astrophysical objects and measure their properties. U of G was also involved in both phases of data collection, and Law, a particle physicist, helped write and test the software used to analyze the data generated.
In 2001, SNO researchers solved the mystery of solar neutrinos that had baffled scientists since the early 1970s, when experiments first detected these tiny particles of matter produced by the sun, only a fraction of the amount that should be arriving on Earth. The first SNO report showed that the electron neutrinos changed into other types of neutrinos in transit to the Earth from the sun. This had deep implications for physics theory because the transformation appears to arise from a finite mass for neutrinos, and the Standard Model of Elementary Particles predicts neutrinos have no mass.
To obtain the latest measurements, SNO scientists added two tonnes of high-purity table salt to the 1,000 tonnes of heavy water at the heart of the detector. Because it contains chlorine, salt provides for three times better sensitivity to detect all the neutrinos, Law said. He added that SNO is the only facility in the world that can make such accurate detections because it includes a giant sphere filled with ultra-pure heavy water that contains heavy hydrogen. Neutrinos passing through break up the deuterium into a neutron and a proton. “This ‘breakup’ is crucial to the measurement process,” he said. Other detectors, which use light water, are not able to make the same correlations.”
In addition to Law, other U of G researchers who are among the more than 130 scientists from Canada, the United States and the United Kingdom involved in SNO are professor Bernie Nickel, now-retired U of G physics professors John Simpson and Robin Ollerhead, researchers Pillalamarri Jagam and Ian Lawson, and graduate student Hendrick Labranche.
A third phase of data collection at SNO will begin after the salt is removed this month. It includes placing ultra-clean helium proportional counters detectors in the heavy water and is expected to provide even further insight into neutrino properties.
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