A joint Fermilab/SLAC publication

Scientists celebrate completion of underground physics laboratory


SNOLAB is one big cleanroom underground. Image: SNOLAB

The elevator that sinks into the Vale Creighton Mine near Sudbury, Ontario, is a gateway to two different worlds. One is Canada’s largest nickel mine, opened at the turn of the last century and still in operation. The other is SNOLAB, a large underground particle physics laboratory, the grand opening of which will take place today.

To enter the mine, each worker dons the expected garb: sturdy work boots, a bulky work suit and a hard hat with a light attached. But arriving at SNOLAB, located about 1.3 miles beneath the earth, requires a wardrobe change.

“Mines are not traditionally known as ultraclean environments,” said SNOLAB Director Nigel Smith. “Keeping SNOLAB that way takes a significant effort.”

SNOLAB, which currently houses eight dark matter and neutrino experiments, is one of about a handful of underground particle physics laboratories in the world. It is the only one that serves as a giant cleanroom.

The walls are covered in concrete, which has been smoothed and painted for easy cleaning. The place looks less like a mine and more like the Batcave or some villain’s high-tech, underground lair. “It is a little James Bond-ish at times,” Smith said.

Most of the 45 to 60 people who enter the lab each day are staff, employed to keep the more than 16,000 square feet of space up to Class 2000 clean-room standards.

SNOLAB’s experiments search for rare processes. Their signals can be obfuscated by the rain of cosmic rays constantly showering onto the earth from space, which is why they are located beneath more than a mile of protective rock.

Signals can also be overshadowed by the radiation emitted by pretty much everything around us. “Even the potassium-40 in your sweat emits gamma radiation,” Smith said.

So everything that enters SNOLAB, people included, must go through a two-step cleaning process. Workers must shower to wash the mine dust off of their skin and out of their hair. They pull on anti-static, coverall “bunny suits” and hairnets. They slip covers over their shoes and gloves over their hands.

At least two times per hour, air systems recycle all of SNOLAB’s air, which is cooled to fight the more than 100 degree heat of the surrounding rock. Workers that enter some parts of the lab must take air showers after lunch to blow away potentially experiment-ruining crumbs.

Although the laboratory is already in operation, today marks the celebration of the end of the latest round of construction. SNOLAB began as a single underground experiment, called SNO, which allowed scientists to learn why fewer neutrinos than expected seemed to be streaming from the sun. It turned out the solar neutrinos were changing types, or flavors, in midflight. Scientists built on SNO’s success to expand the experiment into an entire laboratory underground.

It takes about 45 minutes to get into SNOLAB each morning. But a growing number of scientists are lining up to conduct their experiments there. To them, it seems to be worth the trip.

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