Jenni Adams is part of a large-scale scientific mission to understand a very mysterious elementary particle — the neutrino. At the IceCube experiment in Antarctica, Adams and her colleagues use a creation over a mile long to detect the evidence of the elusive particle. At TEDxChristchurch, the Associate Professor of Physics at the University of Canterbury explains how that works.
The neutrino has a particular ability to pass through almost anything — our bodies, walls, the sun, even “objects so dense that nothing else can escape” — Adams says. Day and night, neutrinos pass through us all, at a rate of about 100 trillion per second. Because of their ghostly ability to pass through things (nearly) without obstacle, neutrinos are tricky particles to detect.
Though it is rare, neutrinos do interact … sometimes. And on the seldom occasion that they do, they produce charged particles, which in turn produce light, which is [relatively easily] detectable. “If we can put enough targets in front of a neutrino,” Adams says, “then we have a chance [of detecting this light].”
At the Amundsen-Scott South Pole Station, the IceCube team built a system designed to detect this light, made up 5,160 in-ice light detectors and minicomputers strung on 86 cables. Why Antarctica? Because with a meters-long ice shelf, it happens to be the perfect setting for catching neutrinos — a place with a built-in large and transparent structure, necessary for catching the rare flashes of light caused by neutrino interaction.
The light detectors at IceCube are housed in extremely pressure-resistant glass and sunk into a hole in the ice on cables that stretch over a mile long with the detectors, or Digital Optical Modules (DOMs), starting at a depth of 1,450 meters and ending at a depth of 2,450 meters.
Adams describes how they got the detectors underground:
“To deploy these cables … first, we used a normal drill to make a hole and then a specially-developed hot water drill, which pumps hot water down into the hole. We can’t just take the ice out of the hole — it’s 2.5 km deep.
It takes two days to melt each hole; it takes around 11 hours to lower a cable down and we have about 30 hours before the ice begins to refreeze again. Then it takes about a month for the ice to completely freeze, and once it’s completely frozen, there’s no way we can get the detectors out, so the detectors are there for good in the ice then.”
“We’re after neutrinos that come from the highest energy regions of the universe, and they have probably a million to a trillion times the energy than the neutrinos produced in radioactive decays, or from the sun,” Adams says.
The DOMs on the IceCube detector detect the light coming from the charged particles post-interaction and send data up to the laboratory via minicomputer. Then scientists go through masses of data — IceCube collects one terabyte of unfiltered data daily and sends about 100 gigabytes to the lab per day — to try and understand the origins of super high energy neutrinos, particles that might reveal the source of ultra-high-energy cosmic rays, which many theorists think could be outside our galaxy.
“There are cosmic rays [charged particles] that have a million times energy than anything we’ve ever created on Earth and actually likely to ever be able to create,” Adams says. “We would love to know where these charged particles come from… It might be something like an exploding star or objects devouring other objects or something we don’t yet know … We know there’s something out there producing all of this energy — but we don’t know what it is or where it is.”
IceCube hopes to find out.
To learn more, watch Adams’s whole talk below: