Al Lipke, educator for the University of Minnesota’s underground particle physics lab in Soudan, Minnesota, was at the Sugarloaf Interpretive Center in Schroeder on July 16, 2011 to lecture on the lab’s projects. He talked about particle beams being shot from Fermilab, west of Chicago. Even though the beams go 450 miles straight through the ground, they usually hit nothing along the way because most of what looks like solid material is actually empty space.
On any given day in the Northland, while tourists wander through gift shops, mothers wrestle children into grocery shopping carts, and coffee shop patrons hash over the local news, five scientists hunker down a half mile under the ground in Soudan, Minnesota, mining the mysteries of the universe.
The scientists—particle physicists—take an elevator down into the old Soudan iron mine about 80 miles west of Grand Marais, 800 feet further from the surface than the height of the Sears Tower, hoping to capture two or three teeny little particles a day, called neutrinos, with a magnet that weighs over six tons inside a 50’ x 40’ x 270’ lab.
The project is called the MINOS experiment – Main Injector Neutrino Oscillation Search – and Fermi National Laboratory – or Fermilab – in Batavia, Illinois, a far west suburb of Chicago, has been shooting neutrinos toward the University of Minnesota’s Soudan Underground Laboratory daily since 2005.
Soudan Underground Lab’s educator, Al Lipke, enlightened and enthralled a group of visitors at Sugarloaf Interpretive Center in Schroeder on July 16, 2011, offering a lesson in the basics of particle physics and explaining how this project could lead to practical applications as well as further exploration into intriguing enigmas like dark matter and dark energy.
The old mine at Soudan was a great spot for the lab because the solid rock above it cuts down on the interference from cosmic radiation that would complicate the readings. “On the surface,” a poster shown by Lipke stated, “a typical adult is struck about a hundred times a second by cosmic rays. In the lab, it’s about once an hour.”
What is being studied
So what is a neutrino? Wolfgang Pauli discovered neutrinos in 1931 upon realizing that energy was disappearing when neutrons decayed into protons and electrons. He theorized that an unknown particle was given off when that energy disappeared. In 1934, Enrico Fermi gave that particle the name neutrino, which means “neutral little one” in Italian. It has no charge and comes in three “flavors”: the muon, the electron, and the tau. Muons are the ones being sent from Fermilab.
Neutrinos are everywhere. While matter is unevenly distributed throughout the universe, the universe contains an average of about 300 neutrinos per cubic inch. Neutrinos are very, very tiny, and since objects are mostly empty space—yes, it’s true – neutrinos usually travel through the 450 miles of rock, dirt, and water under the ground from Fermilab to Soudan without hitting anything.
How neutrinos are captured
The process of shooting neutrinos goes like this: Fermilab accelerates neutrons, pointed in the direction of Soudan, and smashes them into pieces. Neutrinos are separated out and fly through the ground. The neutrinos make it to Soudan just a little slower than the speed of light. The beam oscillates as is goes, creating a swath of particles believed to be as wide as 25 kilometers.
The neutrinos pass through almost everything, since, as previously mentioned, most everything is empty space, even though it doesn’t look like it to the naked eye. They keep going if they don’t hit anything, but occasionally, one hits the nucleus of a steel atom in the target range, giving off light. Bingo! The lab detects the light and knows a neutrino has arrived.
Some of the neutrinos change flavor between Fermilab and Soudan. The researchers are trying to find out what makes the muons turn into tau or electron neutrinos as they travel. The mystery has yet to be solved, but other mysteries are starting to be mined in Soudan as well.
By the way, scientists now think neutrinos might decay over time. According to Lipke, this would bring about the end of the universe.
Dark matter, dark energy
The universe is expanding at a faster and faster rate, Lipke said. A couple of scientists in the 1930s noticed that the spiraling motion of a certain galaxy was much too fast, however, for the amount of mass they could observe. Translation: something else was there.
Even if we could travel the universe, we would only be able to see about 4 percent of the matter in it, Lipke said. The majority of what exists is made up of what is being called dark energy and dark matter, which does not block light. Of that 96 percent of all matter in the universe, scientists are theorizing that 23 or 24 percent is dark matter and 76 to 77 percent is dark energy.
The Hubble telescope has created a three-dimensional picture of the distribution of dark matter in the universe. The next project at Soudan, the Cryogenic Dark Matter Search project, will attempt to learn more about dark matter.
According to the Soudan lab website, scientists think dark matter might be made up of weakly interacting massive particles, commonly known as WIMPs. “Detecting them is challenging because, in addition to their interactions being weak, the WIMPs are moving at only about one onethousandth the speed of light. Because of their small speeds, WIMPs need more specialized detectors that detect minute amounts of energy. The scientists use cryogenic detectors, which means they must be very cold – a fraction of a degree above absolute zero (minus 459.67 degrees F.) Truly the coldest spot in Minnesota.”
Learning more about dark matter will involve things like liquid helium, liquid nitrogen and lead. Lead could interfere with the experiments if it retained the radioactivity it had on ground level. It loses its radioactivity over the course of time if it is kept way underground, however, and because of this, the project will use lead from old sunken ships.
Scientists working on the Fermilab/Soudan project are hoping for a whopping 12 to 16 dark matter events per year.
Applying the research
What good is all this experimentation going to do, especially when money is tight and citizens are urging legislators to cut out unnecessary expenses? Lipke pointed out that basic research has led to our use of electricity, penicillin, transistor radios, CDs and DVDs, CAT scans and MRIs, the atomic clock, and cell phones. Simply put, basic research can be highly useful to modern society.
The neutrino lab at Soudan cost $37 million to build and operates on about a million dollars a year. Experiments have been done in the old mine site since 1981.
More information about the projects and touring the facility as well as a virtual tour can be found at www.soudan. umn.edu.
Leave a Reply