Arthur B. McDonald

Education and Career

Art McDonald was born in Sydney, Nova Scotia, and was the son of an army officer who participated in the liberation of the Netherlands during the Second World War and later served as a Sydney city councillor. McDonald entered Dalhousie University at age 17, uncertain of which area of science to study. After exploring different aspects of science, he discovered he enjoyed solving physics problems. Among his early projects was a summer job measuring gravity along Nova Scotia roads, which revealed an anomaly that led to the development of a gypsum mine. His master’s degree focused on the relationship of positron lifetimes to defects in materials.

McDonald received his Ph.D. at the California Institute of Technology in 1969. Among his influences at the university was Willy Fowler, who headed the Kellogg Laboratory and instilled in McDonald a belief in the importance of encouraging a collegial work environment. McDonald also crossed paths with John Bahcall and Raymond Davis, whose work on neutrino detection influenced his later projects.

Returning to Canada in 1969, McDonald worked as a research officer at Atomic Energy of Canada Ltd’s (AECL) Chalk River Nuclear Laboratories. (See also Nuclear Research Establishments.) Among the projects he worked on was developing a continuous beam polarized electron source involving deuterium (a heavy isotope of hydrogen).

In 1982 McDonald became a professor at Princeton University, where he conducted work on polarized targets and on the measurement of radon gas emanated from materials and extracted from water.

He joined Queen’s University as a professor in 1989 and held several positions there, including University Research Chair (2002-2006) and Gordon and Patricia Gray Chair in Particle Astrophysics (2006-2013). He was named professor emeritus in 2013.

Research Highlights

While working at Chalk River in 1984, Art McDonald became involved in the development of the SNO Collaboration led by Herb Chen and George Ewan. Their vision was the development of an underground laboratory where the deuterium in heavy water would be used to detect different types of neutrinos (among the smallest known particle in the universe). Scientists were long puzzled by models of the sun which predicted that there should have been more solar neutrinos produced than were picked up by detectors. Experiments conducted since the existence of neutrinos was verified in 1956 had all failed.

Shortly after McDonald moved to Queen’s University in 1989, SNO received government funding from Canada, the United Kingdom, and the United States. The project involved 14 institutions. McDonald held several executive positions related to SNO including Director of the SNO Scientific Collaboration (1989-present), Director of the SNO Institute (1991-2003 and 2006-2009) and Associate Director of the SNOLAB Institute (2009-2013). ( See also Neutrino Project.)

Asked in a 2015 interview why neutrinos fascinated him, McDonald observed that they were “fundamental particles that we do not know how to subdivide further, and therefore they make up a very fundamental part of the laws of physics at the most microscopic level, and therefore their properties are extremely important in terms of being able to understand our world in great detail.” He also noted that being able to play with equipment in a 10-storey underground lab was “fun, once you get there.” McDonald believed that a more detailed understanding of neutrinos could unlock information about how energy was generated within the sun’s core and give clues about the evolution of the universe.

The site chosen for SNO was a deep shaft in Inco’s Creighton Mine of Sudbury, Ontario. AECL loaned 1,000 tonnes of heavy water, as it had an excess supply due to declining demand for CANDU nuclear reactors. Reactions occurred around 20 times a day, leaving visible blue streaks of light as neutrinos split deuterium atoms into a proton and neutron. By counting how many atoms were split and comparing that total to the number of reactions that could only be done with electron neutrinos, scientists hoped to discover where the missing neutrinos went.

The experiments at SNO found that neutrinos changed “flavour” during their journey from the sun to Earth, which produced different detection readings. These different flavours are known as: electron, muon, and tau. As the sun only produced electron neutrinos, earlier experiments only measured that flavour and missed the others. They also determined that the flavour changes proved neutrinos possessed mass, which led to a re-examination of the role neutrinos have played in the development of the universe.

The team’s discovery that neutrinos changed flavour was ranked as one of the three greatest scientific breakthroughs of 2001 by Science magazine.

During the COVID-19 pandemic, McDonald led an effort by scientists at the Canadian Nuclear Laboratories at Chalk River, SNOLAB, the McDonald Institute and the TRIUMF particle accelerator in Vancouver to develop a hospital ventilator that could be easily manufactured to meet the increasing demand for machines to supply COVID patients with oxygen. “The idea is that the capability is here in the particle physics community,” he told the Globe and Mail in March 2020. “We’re just trying to exploit it.”

Nobel Prize

Art McDonald was awarded half of the 2015 Nobel Prize in Physics “for the discovery of neutrino oscillations, which shows that neutrinos have mass.” (See also Nobel Prizes and Canada.) He shared the award with Japanese physicist Takaaki Kajita, who supervised a project similar to SNO, the Super-Kamiokande detector, which also showed neutrinos changing their flavour.

Commenting on McDonald’s win, Globe and Mail writer Ivan Semeniuk noted in 2015 that the discovery “will stand as an example of Canadian-led science at its best, with an emphasis on collaboration, a blending of theory with technical prowess, and the combined expertise of both university and government researchers supported by industry and all converging on a single challenging problem.”

Legacy

In 2015, the Arthur B. McDonald Canadian Astroparticle Physics Research Institute was established by a group of institutions. Located and led by Queen’s University, the institute aims to promote Canada’s leadership in the field (see Physics).

At the end of his Nobel Prize biographical sketch, Art McDonald noted that “our results are significant for the basic understanding of neutrinos and that is what we set out to do, for some of us almost twenty years earlier. I am very pleased with the very large number of young people who had the opportunity to have a “Eureka” moment with us and who have gone on to productive careers beyond SNO. This was a very significant scientific result and a very substantial educational experience for all of us, with which I am very satisfied”

Awards and Honours

• Fellow, Royal Society of Canada (1997)
• Medal for Lifetime Achievement in Physics, Canadian Association of Physicists (2003)
• Award of Excellence, Natural Sciences and Engineering Research Council of Canada (2003)
• Gerhard Herzberg Canada Gold Medal for Science and Engineering, Natural Sciences and Engineering Research Council of Canada (NSERC) (2003)
• Bruno Pontecorvo Prize in Particle Physics, JINR, Dubna (2005)
• Officer, Order of Canada, 2006
• John C. Polanyi Award (shared with SNO), NSERC (2006)
• Co-recipient, Benjamin Franklin Medal in Physics, The Franklin Institute (2007)
• Fellow, Royal Society (2009)
• Killam Prize in the Natural Sciences, Canada Council for the Arts (2010)
• Member, Order of Ontario, 2012
• Co-recipient, Nobel Prize in Physics, Royal Swedish Academy of Sciences (2015)
• Companion, Order of Canada, 2015
• Breakthrough Prize in Fundamental Physics (shared with the SNO Collaboration), Breakthrough Prize Board (2016)