Director of the Sudbury Neutrino Observatory. Discovered that neutrinos have mass and that they can change from one type of neutrino to another.
"The research that we are doing is fascinating for the fact that it really bridges the entire universe. We are attempting to understand the most microscopic laws of physics that describe fundamental particles. And, in so doing, we try to understand the most detailed things about the universe, how it was created and evolved, in short the origins of the universe."
Some academics quietly wind down their careers as they near retirement. Not Arthur McDonald.
Particle astrophysics experiments have been the motivation for his research for many years, and he’s not about to leave the exciting work now. In 1984 McDonald became part of an ambitious physics experiment that would hopefully take place in Canada. The project was counterintuitive: they would measure mysterious solar particles from the bottom of a mine.
In 1989, McDonald became the Director of the Sudbury Neutrino Observatory, or SNO as it is more commonly known. The detector was built 2 km underground in INCO’s Creighton mine near Sudbury, and it was completed in 1999 after a decade of construction and financing. After only a few years, it helped particle astrophysicists prove that their model of the Sun was correct. It also showed that neutrinos do have mass, albeit a very, very, tiny one. The discovery changed the laws of physics at a fundamental level.
For McDonald the project harkened back to his graduate research and lessons learned from the Nobel-prize winning physicist William Fowler at Caltech. At that time, researchers in Fowler’s lab were studying the nuclear reactions that power the Sun. However, they were also using the nucleus of the atom to test the laws of physics. “The combination of those two influences, attempting to understand the physics of the sun and other stars and understanding the laws of physics in a detailed way, was extremely powerful,” said McDonald. “Those two interests came together very well in the SNO project and it was at Caltech that I really got the seeds of the interest in the sun and fundamental particle physics.”
The SNO project was also an incredible chance for Canadian scientists to work with colleagues worldwide. According to McDonald there were about 130 scientists from around the world working on the project at any one time. Overall, he said there have been over 270 different authors on SNO-related papers. “This indicates that we have educated a lot of individuals,” said McDonald. “Over a hundred graduate degrees are associated with this project. There is a tremendous team with a wide variety of talents that have contributed to the success of the project; even the people who sweep the floor and keep the facility ultra-clean contribute in a very large way.”
Now, with SNO’s crucial measurements solving what had been called the “Solar Neutrino Problem”, the original experiment has been completed. The last measurement was taken in November 2006, and the last of the heavy water will be returned to the Atomic Energy of Canada Limited by the end of 2007. But that doesn’t mean the lab is being mothballed.
McDonald is working with other colleagues who are leading the development of a new international underground laboratory near the SNO experiment. The new project, called SNOLAB, is the lowest radioactivity laboratory in the world, with an experimental area three times larger than SNO. Experiments in the new SNOLAB will try to answer further fundamental physics questions, such as: What is the origin of all the matter in our Universe? And, what are the dark matter particles that make up nearly a quarter of the Universe’s mass?
Answers to those questions promise to be just as fascinating as the results of the SNO experiment, so you can bet McDonald will be studying the Universe from deep underground for years to come.