In October, The Royal Swedish Academy of Sciences awarded the 2015 Nobel Prize in Physics to Dr. Takaaki Kajita of the Super-Kamiokande Collaboration in Japan and Dr. Arthur B. McDonald of the Sudbury Neutrino Observatory Collaboration in Canada. Both professors received the award for directing research projects that led to the discovery of a quantum mechanical phenomenon known as neutrino oscillations, which in turn proved that neutrino particles have mass.
From 1995 to 2006, Dr. Charles Duba worked at the Sudbury Neutrino Observatory (SNO) as part of his graduate dissertation at the University of Washington. He performed a variety of functions alongside collaborators to put together SNO’s neutrino detector, from assembling the acrylic vessel and designing electronics to coding simulation and data analysis routines.
Dr. Duba, now Associate Dean of DigiPen Institute of Technology’s Faculty Development and Research as well as Program Director for the Department of Computer Engineering, described his role on the SNO in a special presentation to DigiPen students and staff in October.
“This is the acrylic vessel in there,” Dr. Duba said, showing a picture of a massive sphere suspended in the center of a huge underground cavern. “We had to build this. This is, by the way, the largest cavity at that depth. It’s a huge room. And it’s very deep underground.”
The “vessel” resembles a giant golf ball suspended from the cavern ceiling and submerged in tap water. SNO collaborators filled the sphere with deuterium — atomically altered “heavy water” — which could interact with neutrinos as they passed through the detector and create flashes of light called Cherenkov radiation. These flashes of light were then detected and recorded by the incredibly sensitive array of 9,600 photomultiplier tubes attached to all sides of the vessel’s exterior.
Collaborators constructed the SNO 6,800 feet below ground in a nickel mine in Greater Sudbury, Ontario, Canada. Dr. Duba spoke about the remote laboratory in his presentation, including the everyday trial of just getting to the lab from a nearby aboveground station.
“Typically you were expecting about an hour to get there,” Dr. Duba said, “from when you started on the surface to when you’re actually ready to do something underground. But sometimes it could be longer.”
To get to the observatory, team members had to travel down a massive mineshaft elevator capable of holding a hundred people and traveling at 40 miles per hour. When they finally reached their level near the bottom of the shaft, scientists then walked down a mile-long drift (a passageway carved through an ore bed) to a series of cleaning stations, where they washed their equipment and donned special suits before stepping into the actual observatory.
The extreme depth of the SNO — and its geographic location in central Canada — meant the SNO collaborators experienced a dramatic shift in temperature as they made their hour-long descent into the observatory.
“You get down there to that depth, and you’re in the mine. The rock temperature is 105 Fahrenheit,” Dr. Duba said, recounting the lab’s stifling atmosphere. To keep the mine cool and to keep the dust out of the air, operators used hoses and pipes to move water over the walls and floors of the underground cavities. “It was constantly dripping,” Dr. Duba said. “There was water and mud all over the place.”
Neutrinos are subatomic particles created by nuclear reactions, such as the reactions that take place in the sun’s core. While most of these particles simply pass through Earth as they travel from the sun and throughout space, a very small percentage will interact with other particles. Using large underground detectors like SNO, scientists can detect these statistically anomalous neutrinos as they pass through the earth.
It may seem paradoxical to monitor galactic forces from a deep underground laboratory, but the math adds up — neutrino observatories have to be built deep underground to isolate neutrino measurements and prevent interference from cosmic rays or other sources of background radiation.
According to the Sudbury Neutrino Observatory’s website, “Neutrinos are tiny, possibly massless, neutral elementary particles which interact with matter via the weak nuclear force.”
The goal of the SNO experiment was to determine if solar neutrinos oscillated — or changed “flavor” — as they travel through and out of the sun. In 2001, the SNO team published their first scientific results from the experiment, proving that neutrinos have mass and that solar neutrinos oscillate between flavors. The discovery was a huge development for the physics community because it shed light on the “solar neutrino problem” — a puzzling discrepancy in previous experiments that consistently detected fewer neutrinos passing through Earth than expected. As the implications of SNO’s results became clear and accepted, the 2002 Nobel Prize in Physics was given to the original experiments that had discovered the problem.
Fourteen years later, the director of the experiment, Dr. Arthur B. McDonald, was co-awarded the Nobel Prize in Physics in October. Less than a month after that, the Breakthrough Prize in Fundamental Physics Board awarded the 2016 Breakthrough Prize in Fundamental Physics to the SNO team and four other teams leading experiments on neutrino oscillation.
A lot has happened at SNO in the nearly decade-and-a-half that transpired between the publishing of the team’s results and their reception of the Nobel Prize. In 2006, five years after their results were published, the SNO team turned off the observatory proper and returned the deuterium they borrowed to the Canadian government, signaling the completion of the SNO project. The scientists’ experiments were far from over, however.
In place of the SNO, several other projects have been set up in the space — now called SNOLAB — to monitor other subatomic anomalies throughout the galaxy. Dr. Duba proposed one such project, called the Helium and Lead Observatory (HALO), to monitor supernova activity in the Milky Way. HALO can do this by picking up on bursts of neutrino activity from around the galaxy and comparing the bursts with other neutrino detectors on Earth to see if they picked up on similar anomalies.
“[The HALO Project] was one of the things I proposed that we do with our helium-3 proportional counters — the ones I did the electronics for,” Dr. Duba said. He described the project as basically a “long-term supernova search.”
Dr. Duba continues to collaborate and keep in touch with the friends he made at SNO (“I was the best man at two of their weddings,” he said, laughing), though he doesn’t foresee a trip back to the remote Canadian lab anytime soon. Instead, he’s focusing on his role as a professor at DigiPen.
As for SNO, scientists are still analyzing the data gathered over a decade ago, and others are renovating the neutrino detector still buried 6,800 feet underground for the forthcoming SNO+ experiment. These talented physicists and engineers will continue to hone their research deep beneath the earth so that those of us on the surface may better understand the awesome mysteries of the stars above.