McDonald was born on August 29, 1943, in Sydney, Nova Scotia. He graduated with a B.Sc. in physics in 1964 and M.Sc. in physics in 1965 from Dalhousie University in Nova Scotia. He then obtained his Ph.D. in physics in 1969 from the California Institute of Technology. McDonald cited a high school math teacher and his first-year physics professor at Dalhousie as his inspirations for going into the field of physics.
Physicists have been investigating whether or not neutrinos have mass. Since the late 1960s, experiments have hinted that neutrinos may have mass. Theoretical models of the Sun predict that neutrinos should be made in large numbers. Neutrino detectors on the Earth have repeatedly seen fewer than the expected number of neutrinos. Because neutrinos come in three varieties, and because solar neutrino detectors have been primarily sensitive only to electron neutrinos, the preferred explanation over the years is that those "missing" neutrinos had changed, or oscillated, into a variety for which the detectors had little or no sensitivity. If a neutrino oscillates, according to the laws of quantum mechanics, then it must have a mass. In 1984, McDonald's collaborator Herb Chen at the University of California at Irvine suggested the advantages of using heavy water as a detector for solar neutrinos. Unlike previous detectors, using heavy water would make the detector sensitive to two reactions, one reaction sensitive to all neutrino flavours, the other sensitive to only the electron neutrino. Thus, such a detector could measure neutrino oscillations directly. Chen, McDonald, and collaborators formed the Sudbury Neutrino Observatory to exploit this idea in 1984. SNO was to be a detector facility using 1000 tonnes of heavy water located underground in a mine outside Sudbury, Ontario. Chen died of leukemia in November 1987, however. In August 2001, the Sudbury Neutrino Observatory, now led by McDonald, reported observations that directly suggested electron neutrinos from the Sun were oscillating into muon and tau neutrinos. McDonald is a co-recipient of the 2007 Benjamin Franklin Medal in Physics, the 2015 Nobel Prize in Physics, and the 2015 Fundamental Physics Prize for the discovery of neutrino oscillations and demonstrating that neutrinos have mass.
Humanitarian work
In the spring of 2020, amid the COVID-19 pandemic and the ensuing shortages, McDonald became one of the leaders of a project to mass produce mechanical ventilators at low cost. McDonald has stated that the idea came from discussions with his Italian colleagues about the similarities between the requirements of a ventilator and those of particle physics experiments. The design, called the Mechanical Ventilator Milano, is based on the Manley ventilator but uses modern electronics wherever possible. The details, first published on March 23 by about 150 collaborators, were released under the CERN Open Hardware License. The project received the support of Prime Minister Justin Trudeau who anticipated an initial order of 30,000 to Canadian hospitals. Prototypes, which can be built for less than $1,000, are controlled remotely with an interface written in PyQt.
