Putting neutrino detection on ice.

The South Pole, already a popular site for meteorological and astronomical observations, may also provide the ideal location for a neutrino detector. Douglas M. Lowder of the University of California, Berkeley, and his collaborators propose drilling holes 1 kilometer into the Antarctic ice cap to bury an array of photomultiplier tubes for detecting light flashes generated by subatomic particles known as muons as these particles move through the ice. The investigators hope to detect high-energy neutrinos released in astrophysical events such as the cataclysmic gravitational collapse of a star or the accretion of matter in the massive core of an active galaxy. Such neutrinos interact with ice to produce telltale muons.

However, because neutrinos interact only weakly with ordinary matter, neutrino detectors must cover large areas to be effective. An ice-bound neutrino detector offers the key advantage of expandability. Researchers can readily drill additional holes to extend the Antarctic array, thereby increasing its likelihood of picking up and pinpointing the sources of neutrino signals. "Unlike existing and some proposed detectors, there would be no physical limit to its size and structure," the project leaders say.

In the Sept. 26 NATURE, Lowder and his colleagues describe the results of a pilot project carried out in Greenland to ascertain the feasibility of constructing what they call the Antarctic Muon and Neutrino Detector Array (AMANDA). The Greenland experiments demonstrated that polar ice is sufficiently transparent to permit detection of radiation generated by high-speed muons passing through ice.

"We find these results very encouraging and are planning more extensive experiments at the South Pole during the coming austral summer," they report.