Allen Lipke: “That was of interest to the particle physics community of that time but no one ever found one to disintegrate. They’re more stable than what we expected them to be.”
Kelly: “How does that relate to neutrons?”
Allen Lipke: “Neutrons, kind of the sister to the proton, is very unstable in the sense that neutrons not found in the nucleus of an atom have a half-life of about fifteen minutes. So, in fifteen minutes a neutron is going to decay into a proton, an electron, and something else. That something else is a neutrino.”
Meg: “That’s why it’s called the neutrino lab!”
Allen Lipke: “That understanding goes way back to about 1930.”
Kelly: “I knew I should have paid more attention in science!”
Allen Lipke: “Wolfgang Pauli proposed a theory dealing with the idea that we’re missing something in this research. There’s something we’re not seeing. It took until the 1950s to actually confirm that neutrinos existed.”
Meg: “So it took twenty years to get that research going?”
Allen Lipke: “Well, then they fell out of interest entirely until the 1990s.”
Meg: “Is that when the underground lab in Northern Minnesota came about?”
Allen Lipke: “In the late 1990s a lab was proposed to be put into the Soudan Underground mine but in order to do so they had to build a chamber that would be in alignment with Formulab down by Chicago.”
The Soudan Underground Lab.
Kelly: “Why did it need to align with another lab?”
Allen Lipke: “There was a beam that was projected from Formulab underground through the surface of the earth. At a point in Wisconsin they estimated the beam was about six miles below the surface of the Earth. Because the Earth is round, by the time the beam got to Soudan it would be right on the middle of the detector.”
Meg: “What did the detector consist of?”
Allen Lipke: “It was made out of steel plates. They were hung kind of like big stop signs. They were twenty-five feet in diameter but in the shape of a stop sign. There was eleven million pounds of these steel plates put into position in the chamber. In between the steel plates we put in plastic.”
Kelly: “What was the plastic for?”
Allen Lipke: “It’s the means by which we would collect data from interactions between the neutrino and matter, the substance of the detector.”
Meg: “What did you find?”
Allen Lipke: “We would get about two events per day. Two neutrinos per day would be detected coming from Chicago going through the earth. Trillions of neutrinos would pass from Chicago through the earth and go through our detector. Neutrinos are very, very small. The smallest particle in the universe. They hit almost nothing but occasionally one, two, three per day would hit it and that would be our data.”
Kelly: “This makes me feel like there’s so much more to learn and so much left to explore even here on Earth! Is that research still going on?”
Allen Lipke: “That went on through 2016. A new detector was built farther north in Minnesota near the Canadian border.”
Meg: “How does this relate to dark matter and the research that the lab did?”
Allen Lipke: “Dark matter is an entirely different experiment. It started at about the same time that the neutrino experiment started. The current philosophy is that dark matter is a particle. Dark matter interacts with regular matter, the stuff that we think of being protons and neutrons and the elements of the periodic table. We think dark matter makes up about 25 percent of our universe. Dark energy makes up 70 percent of our universe. And the remaining stuff that we know something about makes up 5 percent.”
Kelly: “We know nothing!”
Meg: “What’s in that 5 percent that we know?”
Allen Lipke: “Most of it is hydrogen and helium but the periodic table makes up about .3 percent of the matter that we find in our universe.”
Kelly: “How did they do experiments relating to dark matter if we know so little about it?”
Allen Lipke: “The experiment at Soudan was an attempt to see dark matter. It centered around germanium detectors that were in a chamber that was cooled down to .04 degrees Kelvin which is right next to absolute zero.”
Kelly: “Sounds like a winter in Minnesota!”
Meg: “How did you get a chamber that cold?”
Allen Lipke: “We cooled it down to that temperature using liquid helium and then evaporated it very fast. That whole process is an engineering marvel in my mind all by itself. But we cooled it down to get the germanium crystals to the point where the atoms were barely moving. We had to think of the temperature as being nothing more than molecular motions. So, any little change is going to result in an event.
Kelly: “You said any little change, so did that cause any false results?”
Allen Lipke: “The elevator that brings people down to the twenty-seventh level below the surface ends up about one-hundred-and-fifty feet away from where the dark matter detector was located. All of a sudden, they noticed they were getting an event every so often, all day long. But then at night they stopped having these events.”