Arthur B. McDonald – Arthur B. McDonald Biography

Born August 29, 1943 in Sydney, Nova Scotia, Arthur Bruce McDonald, is a Canadian physicist who received the 2015 Nobel Prize in Physics for discovering the oscillations of neutrinos from one variety (electron, muon or tau) to another, which proved that these subatomic particles had mass. He shared the award with Japanese physicist Kajita Takaaki.

McDonald he received a bachelor’s (1964) and a master’s (1965) in physics from Dalhousie University in Halifax, Nova Scotia, and obtained a doctorate in 1969 from the California Institute of Technology in Pasadena. He returned to Canada that year to be a postdoctoral fellow at Chalk River Nuclear Laboratories in Ontario, where he studied nuclear reactions. He became a senior researcher in 1980 but left the institution in 1982 to become a professor at Princeton University.

In the mid-1980s, McDonald became part of an effort to build a neutrino observatory 2,070 meters (6,800 feet) underground in a mine near Sudbury, Ontario. The observatory was designed to study the solar neutrino problem, in which the number of electrons-neutrinos observed from the Sun was much lower than expected. In 1989 he accepted a professorship at Queen’s University in Kingston, Ontario, and became the first director of the Sudbury Neutrino Observatory (SNO).

Construction began in 1990. The observatory’s detector was a sphere containing 1,000 metric tons of heavy water (water in which hydrogen is replaced by deuterium, an isotope of hydrogen that has a neutron), and 9,600 photomultiplier tubes to detect the Neutrino interactions with heavy water molecules.

Two solutions to the solar neutrino problem were proposed. In the first solution, the nuclear processes within the Sun that generated neutrinos were misinterpreted. In the second, the neutrinos actually had a small mass. If neutrinos had mass, solar electrons-neutrinos could undergo oscillations in which their varying muon or tau would change. By using heavy water, the SNO, unlike previous detectors, could observe all three varieties of neutrinos.

The SNO began observing neutrinos in 1999, and in 2002 McDonald and his collaborators presented their results. The number of electron-neutrinos was even lower than expected. However, the total number of neutrinos (electrons, muons, and tau) was the same as the number of electron-neutrinos predicted by the solar models. The electrons-neutrinos had oscillated in muons and tau. The neutrino, believed to be massless since Wolfgang Pauli postulated its existence in 1930, had mass.

McDonald He became a Professor Emeritus at Queen’s in 2013. He received many honors for his work, including being made an Officer of the Order of Canada (2006).