The World’s Coldest Physics Lab

An overview of the South Pole with the South Pole Station to the left of the runway and IceCube to the right. (Photo: NSF - Photographer: Forest Banks)

On December 18th, 2010, construction of the IceCube Neutrino Observatory in Antarctica was completed.

IceCube is

a massive ice-bound telescope that fills a cubic kilometer of deep Antarctic ice. The main IceCube detector now contains 5,160 optical sensors on 86 strings embedded two kilometers below the National Science Foundation’s Amundsen-Scott South Pole Station.

These researchers used a large water drill to bore 86 holes into the ice of Antarctica. The holes are approximately 2.5 kilometers deep and each took an average of 48 hours to drill.

Next, they installed sensors into each of these holes designed to detect neutrinos.

A sensor descends down a hole in the ice as part of the final season of IceCube. (Photo: NSF/B. Gudbjartsson)

Neutrinos are subatomic particles which are extremely abundant and rarely interact with matter. In fact, as Darren Grant, a University of Alberta physicist explained on this weeks episode of Quirks  & Quarks, 10 billion neutrinos pass through your thumbnail every second! We never notice them though, because they very rarely interact with matter.

However, if you install enough detectors in the right kind of medium, eventually a neutrino will interact with that material and you will be able to see it.

So why ice? Well the Antarctic ice is both very thick and very transparent. When a neutrino eventually interacts with an ice molecule, it will emit what is called Cherenkov radiation. This is the same type of radiation that causes the weird blue glow in a nuclear reactor.

Cherenkov radiation glowing in the core of the Advanced Test Reactor. Via Wikipedia

On Quirks and Quarks, Dr. Grant explains that Cherenkov radiation is kind of like a “an optical equivalent of a sonic boom”. Basically after the neutrino interacts with the ice it will eject a muon from the ice molecule (a muon is an elementary particle similar to an electron, but 200 times bigger). As the muon travels through the ice, it travels faster than the speed of light through ice. This disrupts the electromagnetic field of neighbouring particles and generates the blue glow of Cherenkov radiation, which is then detected by IceCube.

[Aside:  Some of you may be thinking “Whoa! How can it travel faster than the speed of light?”. Be assured that relativity still holds in this situation. That is because the muon is still travelling slower than the speed of light in a vacuum. Since light moves more slowly through ice than it does in a vacuum, the muon will travel faster than light through ice, but still slower than light through a vacuum.]

So why study neutrinos? Well they are quite useful to astronomers because they can travel from distant stars and galaxies without interacting with magnetic fields or matter. Thus they are like a direct messenger from whatever it is the scientist is studying.

Because of IceCube’s size, it is able to detect the highest energy neutrinos, allowing scientists to study supernova, gamma ray bursts and even dark matter.

You can listen to Dr. Grant’s Quirks & Quarks interview here.