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Work winding down on 2 big experiments in Soudan mine

Paul Paulisich (right) of the Minnesota DNR leads a tour group through the Soudan Underground Laboratory in 2005. Behind the group is the lab’s neutrino detector. (File / News Tribune)

The Minnesota Department of Natural Resources is looking for a new tenant to lease space set to become vacant.

That tenant will need to enjoy being deep underground, though — the space is on Level 27 of the former Soudan iron ore mine.

“We’ve got two really big rooms, so if you know anyone looking to rent a really big room a half-mile underground, give me a call,” Soudan Underground Mine State Park Manager Jim Essig said with a laugh.

With two large experiments wrapping up in Soudan Underground Mine’s physics lab, DNR staff are searching for a new experiment to fill the vacancy. Essig said he is hoping to continue having physics experiments in the lab — reached via a ride on a mine hoist — but the next tenant could be a different type of science experiment or an organization that needs a secure location underground.

“We’ll certainly be active looking for other potential tenants. … There’s a lot of investment in (the space),” he said. “Yes, physics experimentation was the reason for it, but certainly there’s space there that’s located in such a location that there may be someone else out there that’s interested in using a facility of that type.”

Minnesota’s first iron mine already draws researchers from an array of science disciplines. Scientists usually hear about its research opportunities through word of mouth from other scientists, Essig said. Microbiologists have completed research at the park and physicists have arrived at the park to find that there was potential to complete other studies while there, he said Wednesday, adding that earlier in the day, geologists had visited to research underground rock.

“It’s been a good promotional thing for us over the years. It’s also led to some of the research because you are a focal point of a certain group of researchers. That often attracts other people who are interested in doing research and they kind of play off each other to a certain degree,” Essig said.

Dark matter and neutrinos

The Soudan mine, near Lake Vermilion, is open to visitors in summer for two tours — one focused on the mine that operated from 1882-1962, and the other on science experiments now conducted in the space.

Essig said the physics lab tours will continue, but after this summer, they may look different as the two large experiments’ equipment begins to be packed up and moved out. Some smaller experiments taking place at the mine will continue.

The experiments run for a finite amount of time to collect data, and the end of the two major experiments at the mine this year was expected, lab manager Jerry Meier said before the hoist came to take him out of the mine at the end of his workday on Thursday. Eight lab staff work at the Soudan mine.

One of the large experiments, the Cryogenic Dark Matter Search, concluded its research last month and its equipment is being prepared for a move to a facility called Snolab in Sudbury, Ontario. Snolab is in the Vale Creighton nickel mine, which is three times as deep as the Soudan mine. Researchers are searching for an undiscovered particle of dark matter and need to go deeper underground than Soudan’s mine to get farther away from cosmic radiation, Meier explained.

“This is basically a particle they believe exists, but haven’t been able to prove it yet,” he said.

The second experiment, the Main Injector Neutrino Oscillation Search — MINOS for short — has been searching for changes, or oscillations, in neutrinos shot in a beam underground to the Soudan mine from Fermilab near Chicago. The funding comes from the U.S. Department of Energy and is administered by Fermilab in a contract with the University of Minnesota.

Neutrinos are the second-most abundant particles in the universe but remain poorly understood; they are referred to as “ghosts” because they have no electrical charge and rarely interact with each other. Detecting oscillations in neutrinos may help determine their mass, and that information could benefit the understanding of the universe’s workings.

MINOS has been in operation since 2003 and has reached the point where it has collected the needed data, said Alec Habig, a University of Minnesota Duluth physics professor.

“It’s getting to the point where more data doesn’t help you so much because there’s already so much of it,” Habig said.

Once Fermilab’s beam goes down for annual maintenance in July, the MINOS detector will shut down permanently, but it’ll take a while for the equipment to be moved out of the mine, Meier said.

“There are things going on. We’re not just packing up and leaving,” he said. “That’s not a small project. The MINOS detector alone is 6,000 pounds of steel plates. That’s going to take a little bit of time.”

From the park’s perspective, staff will need to figure out how to do the lab tours once the detector dismantling begins. The lab tours have been running for nearly 15 years and the lab drew about 2,500 visitors to the park last year, not counting the educational groups, Essig said. The park has seen an uptick in school groups coming to Soudan both for the mining history and the science, he said.

In addition to putting out the word about the lab vacancy, the park has worked with a consultant to figure out different types of activities for which the space could be used.

“There will be something there; we just don’t really know what that’s going to be. Will it be a series of smaller experiments? Possibly. Will we see a real large experiment again? You just don’t know,” Essig said.

Planning for future work

The beam shooting from Fermilab to Soudan is the same one being used by the experiment called NuMI Off-Axis Electron Neutrino Appearance, or NOvA for short, located at Ash River, 30 miles southeast of International Falls.

The neutrinos will continue to be beamed from Fermilab through Soudan to Ash River, giving Essig hope that they’ll be able to bring another physics experiment to Soudan that requires the neutrino beam. NOvA collects data on neutrinos that’s different than what has been collected at Soudan, which is how researchers are continuing to learn more about neutrinos, Habig said.

“We’ll get different measurements on different aspects of the problems. It’ll match nicely with what MINOS has been able to do running for a long time this way,” he said.

NOvA recently finished its first year of data and the first papers analyzing that data are being completed, Habig said. NOvA has about five to six years left to run and is operated by some of the same people who have worked at the Soudan mine, he said.

As they clear out the equipment from Soudan, it can be used in future experiments, Habig said.

A proposed project called the Deep Underground Neutrino Experiment, or DUNE for short, at the Sanford lab in South Dakota’s Homestake gold mine is in the research and development phase, Habig said.

Taking what is being learned with NOvA, they can improve for the next experiment, he explained. DUNE will involve a new beam of neutrinos being sent from Fermilab to Homestake, and researchers will be able to get better measurements in response to questions left unanswered by the neutrino experiments in Minnesota.

“Over the course of the MINOS experiment being dismantled and the NOvA experiment continuing to take data, we’ll be designing and building the new experiment. Each of these things take a decade to design, a few years to build and a decade to run, so we have to keep something in the pipeline at each stage if we’re going to keep planning new things,” Habig said.

The physics lab at Soudan was created in the early 1980s, the brainchild of Marvin Marshak, a physics professor at the University of Minnesota in the Twin Cities. The first experiments were searching for proton decay — but instead of finding that, they found neutrinos behaving strangely. Now MINOS has given them a better picture of neutrinos — after researchers started the experiment with hardly any picture at all, Habig said.

“In science, whenever you look more carefully and make a careful measurement, sometimes you find what you expect and measure it better and sometimes you uncover more questions,” Habig said. “For example with the MINOS experiment, by measuring very carefully how these neutrinos behave, we’ve uncovered other questions that can be uncovered with the NOvA experiment, which led us to design the DUNE experiment in South Dakota in a certain way to fill in the blanks that we’re uncovering.”


Learn more about the experiments conducted at the Soudan Underground Mine at For more information on the state park, go to