Jan 18, 2011

Guide to the Cosmos Newsletter

World’s Largest Ice Cube and Particle Detector

On December 19th, 2010, construction was completed on the IceCube Neutrino Observatory in Antarctica. A cube of Antarctic ice one kilometer (ten football fields long) on each side has been instrumented with over 5000 optical sensors to detect neutrinos coming from outer space.

Neutrinos are the most elusive of all known subatomic particles. (When we figure out what dark matter is, neutrinos may take second place.) Fifty trillion neutrinos zip right through each of us every second, and only one per week actually interacts with the atoms in our bodies. A neutrino can easily pass straight through a trillion miles of lead, with only a 10% chance of “hitting” any of the lead atoms.

Neutrinos come primarily from the Sun, but also from supernovae and other spectacular cosmic events. Because they are almost unstoppable, we hope to use them to look where light cannot penetrate. For example, it takes thousands of years for photons (particles of light) to travel from our Sun’s core to its surface, as they are continually absorbed and re-emitted. But neutrinos blast straight through, reaching Earth in just over eight minutes. By using neutrinos, we can monitor the Sun’s energy production in real time and be forewarned of coming changes in the amount of sunlight we will receive. Neutrinos will also give us an inside view of how stars explode. Even though supernovae can be billions of times brighter in visible light than our Sun, we believe as much as 99% of all their explosive energy is in neutrinos. IceCube will let us see all we’ve been missing.

Antarctic ice is well-suited to making a neutrino detector, providing an enormous mass that is ultra transparent. If a neutrino does hit an atom in the ice, there might be a small flash of light that the sensors will detect from as much as 100 yards away. A high-energy neutrino may produce a trail telling us where it came from and what its energy was. Hopefully this will add a new dimension to our understanding of the universe.

IceCube was constructed by drilling 86 holes, each 1.5 miles deep, into the Antarctic plateau at the South Pole, 800 miles south of McMurdo Station near the coast. The University of Wisconsin-Madison leads this project and developed a special 4.8 megawatt hot-water drill. Each completed hole was equipped with a string of 64 sensors before being allowed to refreeze. Construction began in 2006 and operated round the clock during the short Antarctica summer, when the Sun shines 24 hours a day.

IceCube is an international collaboration, but the U.S. has provided 87% of the project’s $279 million cost.

IceCube is expected to observe 100 neutrino interactions per day, and has already recorded one with over 100 trillion electron-volts of energy, seven times the highest energy expected from the largest man-made particle accelerator, the LHC near Geneva.

We look forward to IceCube discoveries that are really cool.

images from http://www.icecube.wisc.edu/info/neutrinos/

Regards,
Robert
www.guidetothecosmos.com
Author of "Everyone's Guide to Atoms, Einstein, and the Universe"
and "Can Life Be Merely An Accident?"