- In full:
- Arthur Bruce McDonald
- Born:
- August 29, 1943, Sydney, Nova Scotia, Canada (age 83)
- Awards And Honors:
- Nobel Prize (2015)
- Order of Canada (2006)
- Subjects Of Study:
- cosmic ray
- neutrino
- solar neutrino problem
Arthur B. McDonald
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Who is Arthur B. McDonald?
Arthur B. McDonald, born in Sydney, Nova Scotia, Canada, on August 29, 1943, is a Canadian physicist. He was awarded the 2015 Nobel Prize in Physics for discovering that neutrinos oscillate from one flavor to another, proving these subatomic particles have mass. He shared the prize with Japanese physicist Kajita Takaaki.
McDonald's career includes:
* 1964: Bachelor's degree in physics from Dalhousie University
* 1969: Doctorate from the California Institute of Technology
* 1989: Professor at Queenâs University in Kingston, Ontario
* First director of the Sudbury Neutrino Observatory (SNO)
* 2013: Professor emeritus at Queenâs5 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What is Arthur B. McDonald known for in science?
Arthur B. McDonald is a Canadian physicist renowned for his groundbreaking work on neutrino oscillations. This research, conducted at the Sudbury Neutrino Observatory (SNO) in Ontario, Canada, demonstrated that neutrinos change from one flavor to another, proving that these subatomic particles possess mass.
McDonald's work resolved the solar neutrino problem, which had puzzled scientists for years. His findings have had a significant impact on the standard model of particle physics and our understanding of the universe. In 2015, he shared the Nobel Prize in Physics with Takaaki Kajita for this discovery.
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What important discovery did McDonald help to make about neutrinos?
Arthur B. McDonald, a Canadian physicist, contributed to the groundbreaking discovery that neutrinos oscillate from one flavor to another (electron, muon, or tau), demonstrating that these subatomic particles possess mass.
McDonald's work at the Sudbury Neutrino Observatory (SNO) provided direct evidence for neutrino oscillations. SNO's findings revealed that the total number of neutrinos matched predictions, but the number of electron-neutrinos was lower than expected, implying that they had transformed into muon and tau neutrinos. This discovery that neutrinos have mass resolved the solar neutrino problem, which was the discrepancy between the predicted and observed number of solar neutrinos. McDonald shared the 2015 Nobel Prize in Physics for this work.
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What is a neutrino, and why are they important in physics?
A neutrino is an elementary subatomic particle with no electric charge, very little mass, and 1/2 unit of spin. They are subject to the weak force and are the most penetrating of all subatomic particles. There are three types of neutrinos: electron-neutrino, muon-neutrino, and tau-neutrino.
Neutrinos' importance in physics grew with the discovery of neutrino oscillations, which showed that neutrinos have mass, a finding that went beyond the Standard Model of particle physics. Arthur B. McDonald and his team at the Sudbury Neutrino Observatory (SNO) determined that electron-neutrinos change types as they travel from the Sun, which proved that neutrinos have mass. McDonald shared the 2015 Nobel Prize in Physics for this discovery.
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How did McDonald's work at the Sudbury Neutrino Observatory help prove that neutrinos have mass?
Arthur B. McDonald's work at the Sudbury Neutrino Observatory (SNO) was crucial in proving that neutrinos have mass.
The SNO was built to solve the solar neutrino problem, which was that the number of electron-neutrinos observed coming from the Sun was much less than expected. SNO was able to detect all types of neutrinos. In 2002, McDonald and his team announced that while the number of electron-neutrinos was lower than expected, the total number of neutrinos was consistent with solar models. This showed that electron-neutrinos undergo oscillations, changing into muon and tau neutrinos.
Since neutrino oscillation can only occur if neutrinos have mass, this proved that neutrinos are not massless, as was previously thought.
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Why did Arthur B. McDonald win the Nobel Prize in Physics, and how did his discovery change our understanding of the universe?
Arthur B. McDonald, a Canadian physicist, was awarded the 2015 Nobel Prize in Physics for his discovery that neutrinos oscillate from one flavor to another, proving they have mass. This was achieved at the Sudbury Neutrino Observatory (SNO), which he directed. SNO's ability to observe all three neutrino flavors using heavy water was key to this discovery.
This finding resolved the solar neutrino problem, which observed fewer electron-neutrinos from the Sun than expected. McDonald's work demonstrated that the total number of neutrinos was as predicted, but they changed flavors en route to Earth. This proved neutrinos have mass, altering the previous assumption that they were massless and changing our understanding of these fundamental particles.
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Arthur B. McDonald (born August 29, 1943, Sydney, Nova Scotia, Canada) is a Canadian physicist who was awarded the 2015 Nobel Prize in Physics for discovering the oscillations of neutrinos from one flavor (electron, muon, or tau) to another, which proved that these subatomic particles had mass. He shared the prize with Japanese physicist Kajita Takaaki.
McDonald received a bachelorâs (1964) and a masterâs (1965) degree in physics from Dalhousie University in Halifax, Nova Scotia, and went on to earn a doctorate in 1969 at the California Institute of Technology in Pasadena. He returned to Canada that year to be a postdoctoral fellow at the Chalk River Nuclear Laboratories in Ontario, where he studied nuclear reactions. He became a senior research officer there in 1980 and left 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 electron-neutrinos observed coming from the Sun was much less than expected. In 1989 he accepted a professorship at Queenâs University in Kingston, Ontario, and became the first director of the Sudbury Neutrino Observatory (SNO).
Construction started on SNO in 1990. The observatoryâs detector was a sphere containing 1,000 metric tons of heavy water (water in which the hydrogen was replaced by deuterium, an isotope of hydrogen that has one neutron), and 9,600 photomultiplier tubes detected the interactions of neutrinos with the heavy water molecules. SNO had to be deep underground to avoid contamination by cosmic rays; neutrinos, on the other hand, passed through the 2,100 metres of rock umimpeded.
There were two proposed solutions to the solar neutrino problem. In the first solution, nuclear processes within the Sun that generated neutrinos were misunderstood. In the second, neutrinos actually had a small mass. If neutrinos had mass, the solar electron-neutrinos could undergo oscillations in which they would change their flavor to muon or tau. By using heavy water, SNO, unlike earlier detectors, could observe all three neutrino flavors.
SNO began observing neutrinos in 1999, and in 2002 McDonald and his collaborators presented their results. The number of electron-neutrinos was still lower than expected. However, the total number of neutrinosâelectron, muon, and tauâwas the same as the number of electron-neutrinos predicted by solar models. The electron-neutrinos had undergone oscillations into muon and tau. The neutrino, thought to be massless since its existence was postulated by Wolfgang Pauli in 1930, had mass.
McDonald became a professor emeritus at Queenâs in 2013. He received many honors for his work, including being named an Officer of the Order of Canada (2006).
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