'Eureka moment': Canadian physicist describes Nobel-winning discovery

Professors Anne L'Huillier, left, Goran K. Hansson and Olga Botner, right, members of the Nobel Assembly announce the winner of the 2015 Nobel Prize in physics, in Stockholm, Tuesday Oct. 6, 2015. (Fredrik Sandberg / TT)

The road to the Nobel Prize for Physics began more than 30 years ago for Canadian professor Arthur McDonald, who learned Tuesday that he is the co-winner of the 2015 award.

"Back in 1984, there were 16 of us that came together," McDonald, 72, told CTV's Canada AM on Tuesday.

Over time, the group grew to approximately 130 collaborators from Canada, the U.S., Britain, and Portugal.

McDonald led the research group in Canada, where he is the director of the Sudbury Neutrino Observatory, located in a northern Ontario nickel mine two kilometres underground.

McDonald said working 2,100 metres underground allowed scientists to avoid radiation.

"It's the same radioactivity that makes the northern lights glow. We didn’t want our detectors to glow," he said.

McDonald said, in that environment, scientists were able to observe neutrinos that are produced by the same kind of nuclear reactions that power the sun.

The tiny particles are very difficult to detect. McDonald said their size makes it possible for neutrinos to pass through the sun without being stopped.

"So we are able to study the properties of neutrinos and also able to study the nuclear reactions that power the sun in great detail," he said.

The scientists were able to show that neutrinos change their type as they travel from the core of the sun to a detector in the mine, "which means they have mass – something that is beyond the standard model of elementary physics and a real contribution to science in that way."

Realizing neutrinos had mass was "a real eureka moment," McDonald said.

"We know neutrinos have a mass that's greater than zero, and we know very accurately how the sun burns in terms of the nuclear reactions powering it," he said.

McDonald won the award along with Takaaki Kajita of Japan, who oversees the Super-Kamiokande detector. Kajita presented the discovery that neutrinos from the atmosphere switch between two identities on their way to the Super-Kamiokande detector.

The Nobel committee described both discoveries as being of "ground-breaking importance for particle physics and for our understanding of the universe."

McDonald said, while there were rumours of a possible Nobel prize for "many years", he didn't have his hopes up.

"It's the sort of thing where you don't want to create any expectations with something as wonderful as this."

He said, over time, 270 authors contributed to the neutrino research.

"Which means we were able to educate a tremendous number of young people as students and as post-doctoral fellows in the process of doing this," McDonald said Tuesday morning. "Because, fundamentally, we are educators as well as researchers."

Prime Minster Stephen Harper congratulated McDonald in a statement, and said his accomplishment will likely inspire other Canadian scientists.

"I am certain that Dr. McDonald's extraordinary accomplishment will further inspire our scientific community and I hope that it will encourage young Canadians who may be considering science as a career choice across the country."