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Deep Science



Workers in the early 1990s assemble the massive geodesic dome that is part of the Sudbury Neutrino Observatory. Inset: The dome as it nears completion.

Deep in the Canadian Shield, the Precambrian rock that covers more than half of Canada’s land base, miners are going to work.

While gold and diamonds have come out of the Shield, the mineral that employs the most workers is nickel, especially that found around Sudbury, Ont. Each morning a group gathers at the Creighton Mine dressed in overalls, heavy boots and hard hats with a flashlight on the front. While they joke and tell rough jokes about the night before, there will also be a group of physicists, engineers and university students heading for the same depths.

It is not what is there that attracts the second group. It is what is not there.

Two kilometres under the solid rock is perhaps the world’s deepest scientific laboratory, shielded from outside environmental elements more effectively than any other place on Earth. It is believed to be the least radioactive laboratory ever constructed. Deep where the sun doesn’t shine a group of scientists is busy trying to discover, or at least better understand, how the sun works.

The Sudbury Neutrino Observatory is a gem of Canadian scientific research. Here they are studying the nature of neutrinos. Neutrinos are a group of stable elementary particles with no electrical charge, originally believed to have no mass and which travel at the speed of light from the sun and other stars.

As early as 1920, long before the nuclear bomb, English physicist Arthur Eddington theorized that nuclear fusion powered the sun. Understanding and proving how the sun worked turned out to be a much more daunting task. In the 1960s scientists became convinced that ghostly particles called neutrinos were a byproduct of that nuclear fusion.

Neutrinos are the only particles that emerge directly from the thermonuclear furnace at the core of the sun and other stars. Two hundred trillion trillion trillion neutrinos are created in the sun’s core every second.

These subatomic particles can penetrate virtually all types of matter. Most neutrinos would emerge unscathed after travelling through a wall of lead for a whole year. As a brochure for the observatory puts in, “Neutrinos stream out from the sun’s core at the speed of light. Because they reach Earth in minutes compared to the thousands of years it takes other particles to escape from the sun, they are light-speed couriers bearing the news of what’s happening today inside the sun.”

Observing them has proven difficult mostly because of the radioactivity generated by almost everything on Earth. Even the rock deep in the ground presents a problem for the scientists because of its natural radioactivity.

The theory of a neutrino was proposed long before it was ever observed. Italian scientist Bruno Pontecorva proposed the concept in the 1940s when he was conducting research in the nuclear laboratories at Chalk River, Ont., 160 kilometres northwest of Ottawa. Pontecorva later defected to the Soviet Union during the Cold War.

While laboratories in the United States, Japan, Russia and Italy searched for neutrinos, they only found what came to be known as the Neutrino Problem. As neutrinos started to be detected in the 1950s, scientists were only finding one third to one half of what was expected, given the established model of how the sun worked. Either the models of the sun were incomplete, or the electron neutrinos were changing to other types in transit from the sun. While only electron neutrinos are produced at the sun’s core, three different species, or flavours as they are called, can be found on Earth. These are electron, muon and tau-type neutrinos.

The Sudbury Neutrino Observatory, affectionately referred to as SNO, has been dealing with the Neutrino Problem since the early 1990s and in 2002 solved the problem.

To understand the workings of the observatory, Richard Ford, the scientific manager for the water purification systems so important to the observatory, led me and another non-scientist on a tour deep into the ground.

Having picked me up at my motel at 6:30 a.m. we drive southeast of Sudbury through Copper Cliff to the town of Lively, about 20 kilometres away.

Here we take off our clothes except our underwear, don a T-shirt and then get into miner’s overalls. We are given a heavy tool belt, to which we attach the battery unit for a flashlight which is attached to our hard hats.

Visitors taken care of, Ford leads us to a massive change room where he lowers his personal mining gear from a steel basket suspended about 20 feet off the ground.

Once the miners gather for the day shift, we enter the elevator to drop down to the various tunnels called drifts. Miners call out the elevations to which they are assigned. We get out at the second-last stop, 6,800 feet. The miners go one direction while the three of us head in the opposite, walking 1.5 kilometres through blasted rock, potholes and puddles until we come to a steel door.

From there we go into a room much like a high school gymnasium change room. The miner’s overalls come off. We shower and emerge to get a clean T-shirt and new overalls and a plastic hair net, like health care workers often wear, before putting on a new hard hat.

The clean room procedure is complete. Now we are ready to see the observatory.

Creating the observatory was a long process which began with an international team of scientists searching for a mine that could become an underground laboratory. The team was headed by Professor Art McDonald of Queen’s University in Kingston, Ont.

Physicist Doug Hallman, a professor at Laurentian University in Sudbury and the vice-chairman of public relations for the project, had explained his part in the project the night before at the restaurant at Science North centre. One of the key attractions at Science North is a display that is designed for children and the general public to explain the labyrinthine workings of the SNO project. “I got involved with them. We settled on the Creighton Mine since it was still in use. I’ve been involved ever since,” he said.

The first significant solar neutrino experiment was conducted in the mid-1960s by Raymond Davis, Jr., of the University of Pennsylvania. He set up his laboratory in a former gold mine in South Dakota using a moderating factor of 615 tonnes of dry cleaning fluid. Neutrinos transformed atoms in the fluid into atoms of argon, an inert gaseous element that fills about one per cent of Earth’s atmosphere. While scientific theory suggested his experiment should have detected about one atom of argon per day. Instead he only found one atom every two and half days.

Davis would later share the 2002 Nobel Prize for his pioneering work but the Neutrino Problem had not been solved.

Further advances in neutrino research were made by an American-Japanese collaboration that used 50,000 tons of light water for detection and further understanding of the oscillation of neutrinos. In order to build their laboratory in Japan, a tunnel was built into the side of a mountain. The Super-Kamiokande collaboration found oscillation accounts for the creation of a number of muon-neutrinos which could be easily detected by that lab.

Funding for the SNO project was announced in January 1990. The observatory received $70 million in funding. The supporting partners included INCO Limited, Natural Sciences and Engineering Research Council Canada, Industry Canada, National Research Council of Canada, Northern Ontario Heritage Fund Corporation, the Province of Ontario, the U.S. Department of Energy, the U.K. Particle Physics and Astronomy Research Council, Ontario Power Generation and AECL. Participating universities include Queen’s University, where McDonald leads the project, Laurentian University, University of British Columbia, Brookhaven National Laboratory, Carleton University, University of Guelph, Lawrence Berkeley National Laboratory, Los Alamos National Laboratory, Oxford University, the University of Pennsylvania and University of Washington.

The SNO team decided the best agent for detecting neutrinos would be heavy water. They borrowed heavy water from Atomic Energy Canada Limited worth $300 million to set up their experimental lab. What they in fact created was a 10-storey vacuum tube with tonnes of heavy water.

Excavation by INCO crews began in March 1990. Three years went into the excavation alone until November 1994 when the clean room assembly began. What needed to be created was a geodesic dome, 10 storeys in height. Each panel of the acrylic vessel came down the elevator and was carted on small railway cars to the observatory space.

To further protect the vessel it is immersed into 1,000 tonnes of regular water. “We have all the purification systems down here. We have accountants. They are not dealing with money, but are accounting for every ounce of the heavy water, which must be returned,” says Ford.

What one sees is not unusual other than the workers are all wearing the hair nets, hard hats and overalls. They mostly study computers, which are sensing and identifying all the radioactivity in the heavy water and determining which are neutrinos and which are not. One computer has red lights all over, detecting dozens of reactions every second. They are studying these in two ways, one sensitive only to electron neutrinos, the other sensitive to all three neutrino types.

In 2002 the SNO team solved the mystery. Taking data over a 24-month period the observatory’s scientists were able to conclude that neutrinos do change flavour on their way to Earth. The scientists were able to show that 2/3 of the electron neutrinos were changed to other types before reaching the detectors. This analysis also proves that the model of the sun accepted by scientists is indeed accurate.

“There are a number of questions that have been eluding scientists,” says Ford.

The heavy water must be returned in 2007, to be used as a moderating agent in CANDU reactors. Heavy water has a neutron as well as a proton in each hydrogen atom. Because of its sensitivity, more than 3,000 neutrinos a year are observed in the vat of heavy water. Analysis of the readings from the 100,000 light sensors permits scientists to determine energy, direction of travel and time of arrival of each neutrino that interacts.

“A neutrino has no charge. It does not react to alien things,” says Ford. While atoms decay into either an alpha force—or strong force—or as a beta force—or weak force. “Neutrinos will only interact with a weak force.”

“A basic question is how did the sun get to be so hot? If the sun didn’t have mass it would have burned itself out,” says Ford. The 2002 findings also proved that because neutrinos had the ability to mix with atoms they must have mass.

“That also sheds light on the dark matter of the universe,” says Ford. “There has to be a lot more matter in the universe than can be estimated by counting the stars.

“The project has solved all these physics problems in one fell swoop,” says Ford.

Following the publication of the scientists’ findings, McDonald won the 2003 Gerhard Herzberg Canada Gold Medal for Science and Engineering. The prize awarded by the Natural Sciences and Engineering Research Council of Canada gives the recipients $1 million toward further scientific research.

While the observatory will be winding down its work next year, the excitement lies in the future use of the space. The lunchroom of the observatory is filled with sketches of the proposed SNOLab.

“SNO is an experiment. SNOLab will be a facility able to accommodate many types of underground scientific experimentation,” says Ford.

“The proposals are already coming in,” says Hallman. “It will just depend on what the projects are and how good the science is behind them. The one that makes the most sense will get funding.”

With the heavy water having to be returned in 2007 the SNO project is coming to an end. But the future has already been explored.

Various diagrams of the imagined facility have been drawn up. New segments are being built and another space the size of the SNO cavity will be excavated for future scientific work. “There have been underground laboratories tried in Europe, Japan and smaller areas, but North America is the only place where anyone has gone this deep.”

“Advancing scientific knowledge is a long-term effort. A lot of people talk about the technology spinoffs of long-term research as a justification for governments and industry investing in science,” says Ford. “I think it is the human capital that is important. Canada has always been a country of engineers.”

He notes how Canada has led the world in engineering feats such as the Canadian Pacific Railway and great discoveries in medicine. “To flourish you must have good universities. If you don’t the good students will go to other countries. Research would go to the rest of the world. We have to have a substantial amount of science here.”

As the tour ends, Ford uses his cell phone to find out what time the noon elevator would leave, which sounds like a contradiction. But the elevator operates to the schedule of the miners, not the scientists.

“There were a lot of factors that made the project a success,” said Hallman. “We had the funding but most of all INCO is still working the mine. Therefore we have the infrastructure—the lift, the water and the ventilation.”

Hallman says the scientific research produced in Sudbury has led the world on the subject of neutrinos. “And that is good for science and for scientists, for Sudbury and for Canada,” he concludes.


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