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Neutrinos are subatomic particles produced by the decay of radioactive elements and elementary particles that lack an electric charge. They're so tiny that they can pass through solid matter without colliding with any molecules and they travel at close to the speed of light, making them incredible intergalactic messengers.
Ordinary matter is made of neutrons, protons, electrons and neutrinos. Neutrinos are emitted when neutrons transform into protons in nuclear reactions. They are produced in the nuclear reactions in the sun and in those ignited by the collapse of a dying star. Besides the particles of light they are the most common particle in the universe; they are much more numerous than protons and neutrons. IceCube detects the blue light emitted by the nuclear reaction of a single neutrino crashing into an ice atom. Neutrinos are attractive for high-energy astronomy because they are not absorbed in dense sources like other probe particles, and they travel in straight lines from their source.
We are looking for extremely high energy neutrinos that come from supernova explosions, gamma-ray bursts, black holes, and other extra-galactic events. Correlating the number and energy of the detected neutrinos with these events will help us explain their nature as well as help us understand the sources of dark energy and dark matter.
The basic motivation is to understand our Universe, specifically what powers the most energetic engines in the cosmos and fuels the bombardement of cosmic rays to the Earth. We also want to understand the nature of Dark Matter. At the end, the stuff from which we are made is only 4% of the Universe's inventory, whereas Dark Matter is 23%. These are motivations dominantly driven by curiosity, by the dream of mankind to understand our origins, our place in the cosmos, and a far future much beyond our human horizons. But - this is not the full story. As history teaches us, research started as purely exploratory eventually turns to something applicable:
From University of Wisconsin - Madison's Chancellor, John D. Wiley:
Back in the early 1970s, I worked at Bell Telephone Laboratories in NJ. A friend (fellow staff scientist there) was studying the solidification of metals, trying to create solid "blobs" of metal that have no crystalline structure. In other words, he wanted the metal atoms in the blobs to be randomly positioned relative to each other instead of lining up in the regular rows and patterns of a crystal structure. The atoms in glass are randomly arranged, so he referred to his experiments as attempts to create "glassy metals." He found that if he started with molten metal (and atoms are arranged in constantly-changing but random patterns in liquids), and then cooled the liquid quickly enough, it would solidify without giving the atoms time to rearrange themselves into crystals. The rapid cooling was done by "shooting" liquid metal drops at cold surfaces, causing them to "splatter." The solidified splatters were solid glassy metal samples. I remember teasing him that his work was useless because "Why would anyone care? Your samples are impractically hard to produce; They are unstable (re-crystallize upon heating even a little bit); and have no useful function." His response was that no one knew much about the details of the crystallization paths of metals, and they were interesting questions to answer. "Besides, maybe someday there will be a use for glassy metals."
Now skip forward to the mid 1980s: I am working at Wisconsin, having coffee with a friend who is a faculty member in Metallurgical Engineering. We're discussing the diffusion of impurity atoms through various layers of metals and insulators in microelectronic chips. It became clear that most of the diffusion was along the boundaries between grains in crystalline layers. "Wouldn't it be great if we could produce a layer of metal that has no grain boundaries? It would have to be either one single crystal or else be a metallic glass." After lots of thought and some experimentation, we decided we could produce layers of metallic glass that would be very good diffusion barriers. So we did it; we patented it; we published it; and then we forgot about it (moved on to other things). Toward the end of the 17-year life of our patents, we discovered that most major electronics manufacturers were using our idea (infringing our patents). WARF sued them and collected lots of royalties. But, more to the point: an idea that started out as pure scientific investigation of interesting questions thirty years ago eventually (and very unpredictably) yielded a process that is critical to the operation of today's integrated circuits in everything from desktop computers to Game Boys.
Although there is no direct application for the science being done through the IceCube project, a great many inventions have been fueled by research done in pursuit of knowledge and for the sake of discovery. When drilling for the IceCube project oftentimes we advance science in other fields, such as discovering more about the pre-historic climate at the South Pole and the nature of ice. In the end, our goal is to provide insights into the nature of neutrinos and the universe that might someday be used to make the science fiction of today the reality of tomorrow.
IceCube will have a volume of one cubic kilometer. The top of the array of detectors is at a depth of 1400 meters.
The National Science Foundation provides most of the money for construction, about $242 million. Another $30 million comes from our collaborators in Germany and Sweden.
In order to build the IceCube telescope, we had to find the clearest and purest ice we could find in as large a quantity as possible. In most ice, air bubbles and air pockets form which would distort our measurements. The south pole is basically an enormous glacier and consists almost entirely of ice. This ice is under extreme amounts of pressure as more and more snow falls and the water and ice are compressed tightly until it has been rendered into its purest form. IceCube detects the blue light made by the nuclear reaction initiated by a direct hit of a neutrino on an atom of ice. These hits are rare and it therefore requires a lot of atoms, actually a kilometer cube of ultra transparent ice to do the science. The instrumented ice has to be shielded from the natural radiation at the surface, in our case by a layer of 1.5 kilometer of ice covering IceCube. To build a detector of this complexity requires a scientific infrastructure. The South Pole station constructed on three kilometers of clear natural ice presents us with the opportunity to satisfy all requirements and make neutrino astronomy a reality.
The estimated total cost of the project is $271 million.
We expect to complete construction in 2011, but science is even now being done with the partially deployed detector. Optical sensors detecting the blue light tracking neutrinos take scientific data within days of their deployment at depth. Once the detector has been fully constructed it is our hope that researchers from around the world will continue to utilize this new tool for decades beyond.
Once the detectors are frozen in the ice, they will stay there for 25,000 years or so. That is approximately the amount of time it will take for that portion of the ice to migrate to the coast of Antarctica. We can send electronic signals to the detectors and minimally change some of their operations, but maintenance and upgrades are impossible once they are in the ice.
The UW became the lead institution after an evaluation by NSF of proposals from several institutions. Previous experience with the AMANDA project, during which UW drilled successfully 19 holes and deployed over 660 optical modules indicated that UW would be best as the lead institution for IceCube. UW initiated and was the lead institution for the construction of the AMANDA neutrino telescope that delivered the proof of concept for IceCube. It also plays this role for IceCube construction.
World-wide over 400 people are involved in the construction of the observatory, the development of the data analysis tools, and the analysis of the data obtained thus far.
Three people spend the whole year (winter over) at the South Pole for IceCube. Their jobs are to maintain the data acquisition computers and collect data. About 50 people stay the whole year out of all the projects located at the South Pole.
During the construction period, between November 1 and February 15, about 100 people from the IceCube project go to the South Pole—although they are not all there at the same time. Only about 48 people from IceCube are there at one time. The average population of all scientists and support people at the South Pole during the Austral Summer is about 150 people.
You can explore our website for descriptions of the construction, life at the South Pole, and recent results. The National Science Foundation has a web site especially for the activities at the South Pole, http://www.usap.gov/. If you have a specific question and can't find the answer, you can send an email message to contact-us@icecube.wisc.edu.