“I don’t want to do run-of-the-mill physics, I want to do something memorable.” Art McDonald, circa 1970
By Clemente Angiolillo and Ruxandra Dranga
[This article originally appeared in The Bulletin of the Canadian Nuclear Society.]
When the Royal Swedish Academy of Sciences announced Arthur (Art) McDonald as a co-winner of the 2015 Nobel Prize for physics for a discovery the committee said “changes our view of the universe,” his former Atomic Energy of Canada Limited (AECL) colleagues and friends greeted the news with a smile and nostalgic reminisces of Art’s days at Chalk River Laboratories (CRL). Among them are Davis Earle, a retired CRL physicist and resident of Deep River who started working with Art in 1973; and Bhaskar Sur, currently the Director of Canadian Nuclear Laboratories’ (formerly AECL) Nuclear Science Division. Earle’s early work with Art took place in the heady days of basic physics research when they paired up for experiments to study two-photon decay in neutron-proton capture using neutrons from the NRU reactor. Sur started working on the Sudbury Neutrino Observatory (SNO) experiment in 1989 when he was at Lawrence Berkeley National Laboratory in Berkeley, California and continued to work on SNO directly with Art at Queen’s University and later with Davis Earle at CRL. Ultimately, under Art’s leadership, SNO would make a major breakthrough on the study of the behavior of an elementary and enigmatic particle of the universe—the neutrino.
“This achievement is the result of the synthesis of over 30-years of work on particle physics, astrophysics and nuclear science that saw early germination at Chalk River Laboratories,” says Sur. “Later on, preliminary SNO results led to a major leap forward on how to measure sub-atomic phenomena that were never used to this extent before and have also provided new insights into the ‘Standard Model’ of physics, and indeed in our fundamental understanding of the entire universe,” Sur adds emphatically.
Pictured in 1986 in front of building 508 at Chalk River Laboratories, Nobel Prize winner Art McDonald, posing confidently on the far right, and Davis Earle, on the far left, flank the Sudbury Neutrino Observatory’s founding team. The initial spokesman for a solar neutrino experiment using Canadian heavy water was Professor Herb Chen (fifth from right), who proposed the concept in 1984 and tragically succumbed to cancer only a year after this photo was taken.
Even the Royal Swedish Academy of Sciences, which bestows the prize annually, acknowledged the ‘earth shook’ when it noted that the Standard Model of particle physics, which described the innermost workings of matter and resisted all experimental challenges for more than 20 years to this point, was now known to be incomplete. Neutrinos, produced in the core of stars by a fusion reaction, were described in the Standard Model as having zero-mass. Art’s work showed that this assumption was incorrect and revealed that they do have mass as well as other amazing characteristics. The SNO experiments essentially rewrote the balance sheet of the universe and have implications for its origins and nature. After the light-carrying particles known as photons, neutrinos are the most abundant particles in the universe as oceans of them are left over from the Big Bang, and many more are produced in stars and in nuclear reactors. They race through the earth and our own bodies like wind through a screen door and they also come in three different identities, or “flavours,” (a technical colloquialism) — which was the key to their eventual unmasking.
On October 16, 2015, Art McDonald returned home to Deep River’s Mackenzie Community School where former colleagues and current CNL staff packed the Childs Auditorium to the rafters to hear Art talk about the SNO experiment that would define his long career. The focus of his talk was the amazing story of an ambitious, risk-laden project for which McDonald served as Director since 1989, which required the building of the most sensitive neutrino detector created to date. Overall, the project is a remarkable engineering achievement in its own right; a massive construction project that resulted in the creation of an ultra-clean, 10-storey-high cavity, two kilometers underground in INCO Ltd’s Creighton nickel mine in Sudbury. In the centre of the cavity was a 12-meter diameter acrylic vessel containing 1,000 tons of heavy water (worth $300 million and on loan from AECL). If that doesn’t sound ambitious enough, SNO would be the first neutrino detector with the ability to detect all three flavours of neutrinos (electron, muon, and tau) and distinguish electron neutrinos from the other two. The depth of the detector’s location was essential to the study as it reduced interference from cosmic rays by many orders of magnitude. Additional steps were required to minimize interference from other sources of radiation and, in fact, the levels of radiation at the centre of the vessel are believed to be the lowest on earth. Once the facility was established, the rest is history. Although the road to the Nobel Prize was laden with challenges and missteps along the way, the project would yield tremendous results to the team’s knowledge of the universe. For CNL, which has been a forerunner in the establishment of the global nuclear industry since World War II and continues to be on the vanguard of nuclear science and technology, it illustrates how history reaches forward and supports the organization’s brand today. Art and many former AECL employees, like Davis Earle, made incredible contributions to the SNO experiment, and it is difficult to conceive of the experiment’s success without those contributions and time spent at Chalk River Laboratories.
Almost three decades after posing for the grainy, black and white photo (above) with the SNO group, Art would return to Deep River to tell his amazing story of discovery that would define his career and earn him the Nobel Prize.
Bolstering Canada’s ‘big science’ brand
Malcolm Harvey, a former Director of Physics at CRL who worked with Art, recounts a memorable conversation he had with McDonald in the early 1970’s when Art came into his office and hinted at the ‘big science’ work that he wanted to pursue. After settling into a chair in Harvey’s office, Art confided something to Malcolm that he has never forgotten to this day: “I don’t want to do run-of-the-mill physics,” he uttered in a plain-spoken, unanimated tone, “I want to do something memorable.” Harvey recounts that moment with Art with a sense of pride and as if the conversation happened yesterday. Personal achievement and professional admiration aside, the Noble Prize is also a win for ‘big science’ in Canada, whose representative institutions are very few and far between in the nation, and would include CNL’s Chalk River Laboratories; TRIUMF in British Columbia; Saskatoon’s Canadian Light Source; and of course SNO, which was initially a grand experiment and more recently has spun-off SNOLAB. For CNL specifically, Art’s win is a shining reminder that some of Canada’s, indeed the world’s, greatest scientific minds have strode through its doors, and CNL can proudly claim to have employed four of the world’s Nobel laureates for extended periods: John Cockcroft, CRL’s first Director when CRL was still under the auspices of the National Research Council of Canada; Geoffrey Wilkinson, a chemist who was at CRL in its early days; Bertram Brockhouse, who did his pioneering work at the NRX and NRU reactors and devised an ingenious method and technologies to probe the crystal structure of materials; and now of course Art McDonald for SNO.
‘Big science’ is a big investment: Davis Earle reflects on the early days
Art came to Chalk River in 1969 as a postdoctoral fellow and progressed to Senior Research Officer prior to his departure in 1982, and although Davis Earle is not familiar with Art’s early work, he vividly recalls the latter years of his career at CRL. They collaborated on a number of experiments culminating in a search for parity violation in deuterium using the electron accelerator at Chalk River. At the time, the Russians were actively pursuing this line of study and their initial conclusions contradicting the Standard Model turned out to be in error according to Earle as he reflects on the early days of the project.
“Although we were unable to get the statistical sensitivity required, we were realizing what it takes to look for very small signals, and it was just at this time that a suggestion by Professor Herb Chen from the University of California, Irving of a solar neutrino experiment using Canadian D2O and an existing Sudbury mine arrived on our doorstop. At the time we thought ‘this is just the kind of basic research we were looking to pursue’ and we jumped at the opportunity,” Earle exclaims. “I basically turned to it full time as I was doing basic research from the day I walked into CRL, essentially curiosity driven work that contributes to knowledge as opposed to applied research work for industry. By 1984, Art was at Princeton and in addition to teaching he invested considerable time into the Sudbury experiment. Other university professors also quickly came on board as advocates and as early contributors to the project. To get it going, we had to convince funding agencies that: a) it is a good idea with potential; and b) we can do it—that essentially it is worth the investment and the results would contribute to our knowledge. That took another six years and it wasn’t easy as we were competing with other good ideas for the same scarce dollars. But because we had a good idea, and the heavy water—compliments of AECL—as well as the availability of the existing Creighton mine, we felt we had a leg up on the competition for funding dollars and the other experiments we were competing with had to admit our idea was also a worthy one to support.”
Located two kilometers below the earth’s surface, the depth of the detector’s location was essential to the study as it reduced interference from cosmic rays by many orders of magnitude. Additional steps were required to minimize interference from other sources of radiation and the levels of radiation at the centre of the vessel are believed to be the lowest on earth.
Ultimately the team got the money to build and early data revelations were an amazing journey for Art, Davis and company. Earle says one important lesson learned from the experience was that funding agencies sometimes don’t always appreciate that it is not enough to simply fund such big projects. Once you commit to funding ‘big science’ research projects that are breaking new ground in construction and installation, you also have to be prepared to add funds when there are setbacks. “We were ‘boldly going where no one had gone before’ and cost overruns are a reality,” he adds. “In addition, these projects are not-for-profit with no source of income, thus operating funds must also be provided.”
Great science and great scientists enrich us all. They enable technologies that ease our lives, or, as in Art’s case, they show us what’s beyond our horizons and the disciplines that ask the biggest questions and find the deepest explanations are the fundamental sciences. Looking back on Art’s work serves as a testament to what is possible when you set high ambitions, work hard to build support for an intrepid project and assemble the right people as part of a team. It takes drive and dedication to convince groups to support a project with such obvious risk, much less challenge existing scientific knowledge and to make breakthrough discoveries, or what Art framed as wanting to “do something memorable” and not “run-of-the-mill.” Surrounded by family and friends, young and older, on that night Art seemed larger than life among former colleagues and the assembled crowd, and his story of true discovery brought another reward his way—the admiration of peers who are proud to see one of their own achieve such a pinnacle.
Clemente Angiolillo and Ruxandra Dranga work at CNL’s Chalk River Laboratories. Clemente is a writer and communications officer. Ruxandra is a reactor physics analyst.