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Scientists enjoy South Pole summer at 35 degrees below zero

The average temperature during the summer is 35 degrees below zero. There is always a northern wind blowing about 15 miles an hour. When storms rage, they do so with wind speeds of100 miles an hour, blowing snow and ice for miles. Yet several members of the University of Delaware’s Bartol Research Institute have chosen to visit the South Pole regularly in an effort to study atmospheric radiation.

This year, UD researchers Xinhua Bai, Serap Tilav and Gerald Poirier were joined by high school teachers Jason Petula and Mats Pettersson as they embarked on the annual southern expedition from Nov. 15 to Jan. 15. The group was responsible for collecting and analyzing data, maintaining equipment worth millions of dollars and assembling a protocol for the future study of atmospheric radiation.

One of the key aspects of their study lay a mile below the snow the scientists walked upon. The Antarctic Muon and Neutrino Detector Array, also known as AMANDA, consists of multiple phototubes inserted into holes drilled deep into the Earth. They are placed at such a depth as to eliminate particles from the atmosphere, which often act like static on a radio station.

Once locked away under a mile of ice and snow, AMANDA works like “a backwards light bulb,” Thomas Gaisser, Martin A. Pomerantz Chair of Physics and Astronomy and the principal investigator for the project, said.

The sensors of AMANDA collect radiation that has been omitted by cosmic rays and has traveled through the center of the Earth. According to Gaisser, the rays “produce an optical shockwave, like a sound wave or a wave in water.” This wave is much like a sonic boom, but with light.

A second tool used by the researchers is the South Pole Air Shower Experiment, or SPASE, which is used to detect the same particles AMANDA does, only above ground. Because of the rarity of these high-energy particles–there is usually one in the size of a football field during the span of a minute–numerous sensors are laid over 15,000 square meters.

The South Pole is an ideal location for SPASE because of the high altitude, which also works to eliminate unimportant radiation that causes confusion in data. Due to the otherwise undesirable climate, moisture is instantly frozen, eliminating clouds. This cloud-free sky allows particles studied by SPASE into the atmosphere without restraint.

A newly approved project, known as ICECUBE, underwent preliminary engineering testing, with Poirier at the helm. Poirier, who has been with the project since 1992 and built the modules used in AMANDA, had to install a tank of water and make it freeze clear in order to prevent a distorted reading by instruments that would be placed into the tank.

This is no simple task because once water begins to freeze, it expands as much as 10 percent. However, the tanks could not be sealed from the snow and ice often carried by the wind without creating bubbles. Instead, Poirier developed a method that froze the water from the outside in. The center of the tank, which had to remain above freezing, slowly pushed up all remaining air from the water.

The annual trip provides an opportunity to visit the South Pole to more than just Bartol scientists. Each year, there is an opening for two Girl Scouts or Boy Scouts to tour the facilities. This year, however, none were able to attend and, in their absence, the team of scientists flew the flag of Chesapeake Bay Girl Scout Troop 315.

While at the pole, Bai and his colleagues answered a barrage of questions posed electronically by troop members. “The girls were so wonderful with their questions,” Bai said.

Graduate students are also encouraged to make the voyage. “I see the need for graduate students involved in the immediate and long-term future,” Poirier said. “This is a big project.” Interested students should contact Gaisser.

Feb. 4, 2002

Kaytie Dowling