Science

Probing the deeps for cosmic clues

What researchers find in Sudbury might revolutionize science

DANYLO HAWALESHKA September 2 1996
Science

Probing the deeps for cosmic clues

What researchers find in Sudbury might revolutionize science

DANYLO HAWALESHKA September 2 1996

Probing the deeps for cosmic clues

Science

What researchers find in Sudbury might revolutionize science

DANYLO HAWALESHKA

They call it “The Cage”—and for good reason. Forty miners are squeezed in shoulder to shoulder, before the operator slams the gate to the confining elevator shut. The only light comes from headlamps slung over miners’ shoulders. Faces are hidden in shadow. At a signal from the operator, the lift starts its plunge, bumping and clanging into the depths of Inco Ltd.’s Creighton Mine on the outskirts of Sudbury in Northern Ontario. Ears pop with the sudden change in pressure. Also heading more than a mile underground are a handful of scientists searching for the subatomic secrets of the universe. Together, they are building one of the most eagerly anticipated research facilities in the world: the Sudbury Neutrino Observatory, a $70-million engineering marvel housed in a 10-storey cavern blasted out of rock beneath the Canadian Shield. Once construction ends early next year, SNO will be a scientific facility unique in the world. Says SNO’s director, Art McDonald: “This is groundbreaking work—no pun intended.” Unintentional humor aside, SNO is nothing to laugh at. Physicists will use the facility, begun in 1990, to observe neutrinos: ethereal particles produced in astronomical quantities by stars such as the Earth’s sun. Scientists hope neutrinos will help explain why the universe weighs only one-tenth of what it should, once all the stars are added up, and perhaps when the universe will come to an end. As well, there is the allure of discovering the unforeseen.

Researchers are building SNO in a mine because neutrinos have the ghostlike ability to zip through almost everything—including humans. By burying SNO underground, the observatory’s sensitive detectors will be protected from disruptive cosmic radiation, while the neutrinos themselves will have no trouble penetrating the Earth’s surface to reach the “telescope” 6,800 feet below. But just how much research will be done is not yet clear. The international team of scientists is supported by funding from three nations. Canada, the U.S. department of energy and Britain’s Science and Engineering Research Council are paying for the construction, with substantial contributions from Inco and Atomic Energy of Canada Ltd. (AECL). Canada’s Natural Sciences and Engineering Research Council (NSERC), meanwhile, has yet to decide whether SNO will receive all of the $4 million needed to fully fund the first year of operations, a decision expected by March. “I don’t think there is anyone who foresees that there will be no money to run SNO nextyear,” says McDonald. “It’s merely a question of quantity and adequacy.” Neutrinos—the name means “little neutral ones”—are one of nature’s basic building blocks, indivisible as far as anyone knows, and poorly understood. What is known is that the sun is a prolific source, producing 200 trillion trillion trillion every second. In an instant, an exploding star, or supernova, disgorges 1,000 times more neutrinos than the sun will in 10 billion years. And they are as elusive as they are numerous: billions pass through human bodies every second without striking anything (the one or two that do during a person’s lifetime cause no harm).

Strangely enough, physicists and astronomers think there ought

to be more neutrinos coming from the sun. One possible explanation is that prevailing theories of how the sun works are wrong— which, if true, would turn astrophysics upside down. Another theory suggests a link to the fact that there are three types of neutrinos, or “flavors,” known as the electron-neutrino, muon-neutrino and tauneutrino. The theory suggests that the “missing” neutrinos may actually be transforming from one flavor to another—a transformation perhaps unnoticed because observatories inlltaly, Japan, Russia and the United States cannot distinguish between the three. SNO, however, will be the only facility capable of doing so.

Kevin Lesko, a physicist at Lawrence Berkeley National Laboratories in California, has his own take on neutrinos: “If you count up all the stars,” Lesko says, “the universe doesn’t yeigh enough.” The uni-

verse’s so-called dark matter, he says, is where the balance of weight is believed to be. But what is dark matter? While it has never been seen by the eye, dark matter’s existence has been deduced by measuring the gravitational force that keeps galaxies spinning and orbiting the way they do. SNO will help determine whether neutrinos, in the language of science, have mass. If they do, they would be a critical part of dark matter since they easily outnumber anything else in the universe and their mass would exert significant gravitational pull on the expanding universe. That would then affect scientists’ understanding of whether there will someday be a Big Crunch—a time when the universe reverses its present expansion and caves in on itself.

But for the moment, the trick is to catch a neutrino. That objective drives the scientists in the dark lift, which finally stops at the 6,800-ft. level, bobbing unnervingly at the end of its monstrous cable. The walk to the observatory is more than a kilometre long. Even though it is still far from the Earth’s molten core, the temperature here would be 40° C, if not for the cooling effects of roaring ventilation fans. Dust hangs like mist. Boots are scrubbed at the entrance to SNO, and the mine and its dirt are left behind. Inside, visitors must shower, don new clothes, boots and a hair net before going through a final “air shower.” Dust is strictly controlled because it can carry naturally occurring radioactive particles, which in turn could interfere with SNO’s measurements. Upon completion, the centre of the observatory will have the lowest level of radioactivity of any manmade place in the world. In terms of cleanliness, says Doug Hallman, a Laurentian University physics professor, “we’re in the same ball park as an operating room.”

Before there was a sterile observatory, there was a hole in the ground in need of digging, a task that fell to Philip Oliver, SNO’s geotechnical consultant. It was Oliver who helped decide where the keg-shaped, 33mby-22m cavern housing the observatory would go. Enormous lateral pressure exerted by tectonic plates pushing against each other required judicious planning: in the wrong location, without appropriate rock support, the cavern would implode. Oliver, a 31-year mining veteran, tested core samples for strength and elasticity and chose a stable site at the 6,800-foot level, well away from the nickel ore still being mined at Creighton. The exca-

vation took six separate blasts, and not all went as planned. Before one explosion, Oliver placed himself in such a way that he had about 300,000 cubic feet of tunnel space between himself and the detonation site— enough to avoid the shock wave. One problem: the blast actually unleashed more than a million cubic feet of gas. The spent fumes blew right by Oliver. “It was just like a gale,” he says. “I had to hold onto something to keep from falling on my ass.”

The dust from that incident has long since settled. Today, most of the major work is done. SNO’s controlroom floor sits snugly anchored in the rock face near the top of the mammoth cavern. Suspended from the floor, extending into the cavity below, is the observatory’s “lens,” a 12-m-wide, clear acrylic sphere. The sphere will be filled with 1,000 tons of heavy water, normally used as a moderator and heat-transfer agent in CANDU nuclear reactors. The non-radioactive water, produced by Ontario Hydro and on loan from AECL, has an extra neutron in each hydrogen nucleus and is especially sensitive to neutrinos. Of the trillions of neutrinos passing through the sphere each day, roughly 20 are expected to collide with a neutron in the centre of a heavy-water molecule. The collision will emit an electron, which in turn will be detectable as a faint flash of light. That flash will be picked up by 9,500 light sensors, called photomultipliers, embedded in the geodesic sphere that surrounds the heavy-water vessel. The two concentric spheres will themselves be immersed in ultra-pure water to further shield the heavy water from unwanted radioactivity. The shielding will be so thorough that the centre of the heavy-water vessel will have the lowest point of radioactivity ever created. Says McDonald, who also teaches physics at Queen’s University in Kingston, Ont.: “It’s like building a ship in a bottle.”

If this ship of sorts is to set sail, it will need Gerry Lloyd, SNO’s mine co-ordinator who, like Oliver, was coaxed out of retirement after more than three decades of mining. On Lloyd’s broad shoulders rests the responsibility of getting everything needed to build a 10storey observatory down a narrow mine shaft. “Our next big challenge,” Lloyd says, “is getting the heavy water underground without losing a drop.” McDonald deadpans: “Don’t worry, it’s only worth $300 million.” On the cost, some parliamentarians question whether

the federal government had caved in to scientists. In times of fiscal belt cinching, basic research like SNO is a tough sell. Few know this better than Ottawa’s point man for the project, Jon Gerrard, secretary of state for science, research and development. “We’re going to have some long-term payoffs from this,” says Gerrard, “even though we don’t know precisely where the economic benefits of the neutrino are right now.” It was only in March that Gerrard was finally able to confirm that SNO would get its last bit of funding to complete construction. Still, there is hope. While NSERC has not finalized how wide it will open its wallet for SNO’s operating budget next year, the agency’s long-range planning has nevertheless declared that the observatory remains its pre-eminent funding project in subatomic physics. In order for Canada to become a world leader in space science, it seems clear that the country must boldly go where no one has gone before—to catch the elusive neutrino. □

THE NEUTRINO RIDDLE