Ever since its discovery in the early 20th century, cosmic radiation
has been one of the most intriguing phenomena in nature. Although many
of its properties are nowadays well-known, some puzzles still remain
to be solved. One of these is the question of chemical composition:
what kinds of particles make up the cosmic ray flux observed at Earth,
and in which proportions? At energies above ~ 100 TeV, the primary
particles cannot be studied directly, since the flux is too low. Any
equipment light enough to be carried to the top of the atmosphere on
board a balloon, or into outer space with a satellite, is too small to
detect any significant number of primary particles. The only
possibility is to use surface detectors with huge areas, which can
study the air showers induced by primary particles interacting with
air molecules at the top of the atmosphere.
One such surface detector is IceTop, one of several components that
make up the IceCube neutrino observatory. Located at the surface of
the Antarctic ice sheet, some 3000 meters above sea level, and
covering an area of almost a square kilometer, IceTop is uniquely
positioned to study the properties of cosmic ray air showers.
In this talk, I will give an overview of cosmic rays and air showers,
discuss the IceCube neutrino observatory and in particular its IceTop
component, and present a new method of assessing the chemical
composition of cosmic rays.