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.”
Kelly:“Was it the elevator?”
Allen Lipke: “Yes. The vibrations coming through the rock and into the chamber were resulting in detection. Also, we were still getting quite a bit of cosmic radiation.”
Meg:“Tell us more about that.”
Allen Lipke: “Being at that level [half a mile underground] you and I would get about one hundred cosmic ray particles hitting us per day. On the surface we would get one hundred cosmic ray particles hitting us per second. So, a huge difference, obviously.”
Kelly:“Did that affect the data?”
Allen Lipke: “The cosmic rays were hitting the detector, going through lead shielding, going through the safeguards to try to filter out junk and background noise. It wasn’t sufficient to block it all. But yet the Soudan experiment continued and we ended up at the point where we were at our maximum.”
Meg:“Is that research still going on?”
Allen Lipke: “That research was taken out around 2015. The continuation of that research is going up to Ontario, Canada. It’s in a copper nickel mine that’s still active about a mile and a half below the surface. It’ll be deeper and with that greater depth will have less cosmic radiation.”
Meg:“So, what exactly is dark matter?”
