This morning, Jim Madsen, physics professor and IceCube researcher from the University of Wisconsin-River Falls, arrived to the PolarTREC training. I and the other KSTF Fellows spoke with Jim at length about the project, including expectations and our roles as PolarTREC teachers. Jim enlightened us about the nature of neutrinos and how the IceCube detector works to detect them. We had a lot of questions for Jim about neutrinos and how we can study them!
What is a neutrino? * neutrinos are subatomic particles, related to electrons but with no electric charge. They pass through regular matter unchanged (except in rare cases). If it doesn't interact, there is no way to detect it, making it effectively invisible (consider: for our eyes to detect light, the light must interact with molecules in our eye - if it didn't interact, we couldn't see it!)
This cute little feller is a
Where do these neutrinos come from? * Neutrinos can be created due to radioactive decay of elements like potassium. Nuclear reactors and bombs can create neutrinos; the sun and other stars create neutrinos. But these are "low" energy neutrinos, not what IceCube is trying to detect. IceCube is looking for high energy neutrinos created in "cataclysmic" galactic events, such as collisions of black holes and perhaps mysterious events called gamma-ray bursts. How can we detect an "invisible" particle? * On the extremely rare instance when a neutrino hits the nucleus of an atom, it ends up creating a new charged particle which flies through the ice at very high speeds. As this new particle moves though the ice, it causes a dim trail of light called "Cherenkov radiation."
this light is detected by hundreds of sensors buried deep in the ice. The scientists use data from the sensors to determine the energy of the original neutrino, and the direction from which it came.
this energy and direction information gives us clues about about cataclysmic events in the universe.
neutrinos may give us insight into the nature of "dark matter." How many neutrinos are out there to detect?
Each second, about 100 trillion neutrinos go through your body. In your entire lifetime, just 1 single neutrino might interact with an atom in your body.
So a detector the size of a person would detect 1 neutrino in a hundred years. The IceCube detector is huge (a cube 1000 meters on a side!) so there are more chances to "catch" neutrinos. Over the course of an average day, 1,000,000,000,000,000,000,000,000,000 (a billion billion billion!) neutrinos might pass through the the IceCube detector.
The researchers predict that each day about 1,000 of those neutrinos will crash into a nucleus and be detectable. That's about 1 in a million billion billion (that's pretty rare!) Why do we want to study neutrinos?
neutrinos give us a deeper understanding of the universe!
pursuit of scientific ideas can often lead to useful applications years or decades later... who knows what we may be able to do with this knowledge 50 years from now?