AGO Update
The weather is getting better, so hopefully our team will be heading to AGO 4 soon. This morning I woke up to blue skies and the twin otter looked ready to go. Unfortunately, it was going to place fuel at a cache not go to AGO 4, since there is still bad weather at AGO 4.
The twin otter we will eventually take to AGO 4 prepares for a fuel cache trip.
The IceCube Project
Yesterday I took a tour of the IceCube project, which is one of the largest research projects at the South Pole Station. Sven Lidstrom gave three other people and me a tour of the facility. IceCube is trying to detect neutrinos. The purpose of the project is to look at the galaxy through a new lens. Galileo mapped the galaxy by looking at the light coming from stars. IceCube hopes to map out the galaxy by looking at neutrinos. This is similar to the South Pole Telescope's attempt to understand the galaxy by looking at the cosmic microwave background. By using different wavelengths or lenses to map out the galaxy, scientists are able to discover more.
The building that houses the IceCube project sits at the edge of South Pole Station.
What is a neutrino?
A neutrino is a subatomic particle. That means it is smaller than atoms. Neutrinos are very small and do not have an electric charge. Neutrinos are not affected by electromagnetic forces, which allow them to move a very large distance without being affected by matter. Neutrinos are constantly moving through us without any incident. As you read this, it is estimated that a trillion neutrinos move through your hand each second!
Recording the neutrinos
Neutrinos are very hard to track since they are so small and have no charge. Every once in a while, a neutrino will hit another particle, releasing energy and creating a muon--another subatomic particle. This is rare and hard to record but the IceCube project is trying to capture these collisions by putting sensors in the ice. The South Pole is a great place to try to record neutrinos because it has pristine ice that is thousands of meters deep. The scientists look down into the ice for neutrinos, since they can travel through the matter. The ice slows down the speed of the neutrinos.
Sven Lidstrom and Michelle Brown pose by an example of a DOM which records neutrinos in the ice.
The picture above shows the sensor that IceCube uses to record the neutrino collisions. It is called a DOM, which stands for Digital Optic Module. The DOMs are placed in deep holes in the ice. There are 86 holes in the ice that stretch out to a cubic kilometer. A string is placed in each hole with 60 DOMs attached to it. That is a lot of DOMs!
Drilling the holes
Since the holes for the IceCube project are in the ice, the team used a hot water drill to make them. The hot water drill used 90 degrees Celsius water and 200 psi of pressure, to create holes that were about 45 cm wide. Each hole took about 48 hours to drill, drilling at about a meter/minute. Although the melted water was funneled out of the upper part of the holes, it remained in the bottom part of the holes since it helped create more clear ice that the DOMs need to record data.
Orange flags spread out over a kilometer mark the DOMs that are buried in the ice.
IceCube Construction
Constructing the IceCube project required a lot of resources. It took four plane flights to carry enough fuel for each hole! Each DOM cost about $10,000 - 15,000. There were 33 drillers who worked 3 different shifts. The group even brought in their own cooks to help accommodate all the people on their team. 250 scientists from 35 institutions and 15 different countries are involved in the project!
Observing Collisons!
The DOMs send data back to computers at the IceCube station. Every DOM has its own computer. That's a lot of computers! When a neutrino hits a particle or atom, it creates a wave of photons. The DOMs record where the energy is coming from and can trace the interaction backwards from where it started. The DOMs record around 5000 interactions per second, but they often originate from the surface of the ice, so it is unclear whether or not they are neutrinos. However, occasionally the DOMs will record interactions originating from the bottom of the ice, which scientists can infer are neutrinos. The IceCube project sees about 10,000 neutrinos a year, mostly from the atmosphere. After touring the hundreds of computers, Sven showed us a computer that showed the interactions that a DOM had just recorded.
A computer screen shows an event recorded by one of the DOMs. Like many of the recorded events, this one comes from above the ice so it is unsure if it is a neutrino.
ARA: The next generation of IceCube
A new project is under development to record higher energy neutrinos: ARA (Askaryan Radio Array). During our tour we spoke with Kara Hoffman, a scientists in the ARA project. Instead of using DOMs and recording the photons and muons, ARA will use radio waves to record interactions. When neutrinos interact, they give off a radio signal. These signals can travel around 1 kilometer through the ice. This project will only go 100 - 200 meters into the ground but will spread out to 100 square kilometers. The research group is completing its first installation of radio antennas and is already collecting data. They are not expecting to record as many neutrino interactions as the IceCube project, since the neutrino collisions they are recording are from higher energy neutrinos and are more rare. They expect to collect around 5 neutrino collisions a year.
Kara Hoffman poses with Michelle Brown after explaining the purpose and details of the ARA project.
This project is also trying to better understand the galaxy. If they are successful, they may also help answer a question that has mystified scientists: does the radiation in the universe come from a heavy iron ion or from a proton? Scientists have recorded radiation from space 1911, but do not know what it originates from. If ARA records many high-energy neutrino interactions, it will support the theory that the radiation in space comes from protons. However, if ARA records fewer neutrino interactions, it will support the Iron ion theory, since the iron ions are larger and the collision will be less dramatic.
Visiting the ARA Radio Antennas
An engineer for the project, Robert Young, took us out to the edge of civilization on the South Pole to see the ARA radio antennas. It was incredible to see the ice extend for miles as a flat eternity!
Out at the edge of the ARA project, there is nothing but ice and sky for miles!
We were transported to the radio antennas on the back of a snowmobile. The three other visitors and I held on tight as we flew over the ice!
Michelle and the other visitors smile after being transported on the back of a snowmobile.
We also visited a drill site, where a hot water drill was drilling the 100 meter holes for the radio antennas.
Scientists drill 100 meter deep holes for the ARA project using a hot water drill.
Questions
How is the South Pole Telescope project similar to the IceCube project? How is it different?
Do you think researching neutrinos is valuable for science? Why or why not?
Math Connection
If the DOMS are placed in 86 holes spread equally apart within a square kilometer, what is the average distance between each hole?
If there are 60 DOMs in each hole, and 86 holes, how many total DOMs are there?
If the hot water drill is at 90 degrees Celsius, what is that in Fahrenheit? Use the following equation to calculate it: F = 9/5 (C + 32), where F is Fahrenheit and C is Celsius.
If it takes 48 hours to drill each hole for the DOMs, and the drill rate was 1 meter/minute, how deep was the depth of each hole?
The DOMs record 5,000 interactions a second, however most of them do not originate from under the ice and cannot be verified as neutrinos. If 10,000 neutrinos are detected from below the ice per year, what is the ratio of neutrinos detected from below the ice to total interactions in one year?