SOUDAN, MINN. – The lab sits a half-mile underground, a three-minute trip by mine shaft, so that experiments on the universe’s tiniest particles won’t be interrupted by noisy cosmic rays. But on a recent afternoon, the physics lab was a different kind of quiet, its once-buzzing computer fans silent.
It’s about to get quieter.
Research projects at the Soudan Underground Mine, including a high-tech hunt for elusive neutrinos, are shutting down. The lab’s signature experiment — an enormous detector that captures glimpses of neutrinos fired at northeastern Minnesota from Illinois — recorded its final data in late June.
The University of Minnesota is moving out of the mine as the field’s latest research shifts to newer, deeper labs in Canada and South Dakota.
“Although we tried over the last 15 years to show that the next, big project should be at Soudan, we have not been successful,” said physicist Marvin Marshak, the U professor who spurred the lab’s creation in the early 1980s. “Science moves on.”
Summer tours of the mine at the Lake Vermilion-Soudan Underground Mine State Park, Minnesota’s first iron ore mine, will continue. But tours of the physics lab — which Popular Science magazine once named the No. 1 nerd road trip — will wrap up this fall as the detector is broken down.
That work involves slicing hundreds of 27-foot-wide steel plates, which hang in a neat row like a giant file folder, into pieces small enough to make the journey back up the narrow mine shaft.
One day last week, a few interns unplugged thick fiber-optic cables, wrapping their ends with bright tape.
“We calculated that there are 15,500 of these on the actual detector,” said Emma McDonnell, a student at Northwestern University in Evanston, Ill. She wrapped a few cables around her shoulder and turned to Jerry Meier, the lab supervisor. “Jerry, do we actually have to take all 15,500 off this summer?”
“Half of them, yes,” Meier said.
Since 2003, researchers have been using this detector to better understand neutrinos — and, as a result, the universe. The subatomic particles are so small and so tricky that the massive machine can’t measure them directly.
“It’s like shooting into wood with an invisible bullet,” Marshak said. “You can’t see the bullet, but you can see the splinters that come out.”
The detector, part of an experiment called the Main Injector Neutrino Oscillation Search, or MINOS for short, is looking for neutrinos sent 455 miles from the Fermi National Accelerator Laboratory (Fermilab) near Chicago. The neutrino beam there is one of just two in the world, Marshak said.
Because they zoom through matter, neutrinos need no tunnel. Physicists are interested in how long that journey takes, and how the tiny bits change along the way.
For at least the next five years, the Fermilab beam will point beyond Soudan, to a newer physics facility in remote Ash River, near International Falls. A new, souped-up beam will target the Homestake Mine in South Dakota, a gold mine turned underground research facility. Several U researchers, including Marshak, will continue their work there and in Europe.
“The people interested in this topic wanted a new, bigger and better beam — and a bigger and deeper lab,” Marshak said. “Fortunately for the science, they’ve discovered exactly what they need in South Dakota.”
At one time, the Soudan detector was cutting-edge. It was built using materials and machines brought below ground, “a proverbial ship in a bottle,” said Meier, a former Navy photographer who took thousands of shots of the process.
He pointed to crates of shelving, cables and carts stacked in a room behind the detector. Each trip up the elevator shaft costs about $37, he explained, “so when we get stuff down here, it generally stays down here.
“We’ve got 30 years worth of extreme basement hoarding going on here,” Meier said.
Future uses uncertain
A dozen people donned hard hats, then squeezed into the metal box about to be lowered 27 stories below ground. Miners once took the same trip down.
“We’ve replaced components,” the tour guide told them, “but this is all 1924 technology.”
Last year, about 4,000 people toured the physics lab, according to Jim Essig, park manager. Tours of the historic mine are more popular, with about 30,500 visitors last year.
“We’re still going to be conducting the tours we’ve become famous for,” Essig said.
The Minnesota Department of Natural Resources hired a consultant to help look for new tenants to fill the cavernous lab. The department is open to uses beyond research, such as storing large servers or housing a business accelerator.
Essig is hoping for research projects, he said, pointing out that a few, smaller experiments remain in the space. But the MINOS experiment isn’t the first to leave.
Early this year, a major project of the Cryogenic Dark Matter Search left the Soudan lab for a space in Sudbury, Ontario. That experiment, which is looking for heavy particles that could be keys to dark matter, “is getting bigger and going deeper underground,” Meier said.
The experiment’s clean room in the Soudan lab now stands empty, printouts of intricate plans still taped to its walls.
Meier, who started in the lab 27 years ago, said it’s strange to see the place so empty, so quiet. Strange to consider that steel plates bearing the signatures of researchers and politicians, including congressman Jim Oberstar, will soon be cut and sold.
“I hate to see it go,” he said. “But we’re not deep enough, we’re not far enough away.
“So we had a couple strikes against us.”