The earth is constantly bombarded by charged particles from the cosmos. These cosmic
rays have energies which can be as high as 100 million times higher than those produced
in the LHC accelerator. Although they were rst discovered 100 years ago, the details of
the energy spectrum and of the composition of the cosmic rays are still not well known. In
this project we want to determine the energy spectrum, and the composition, at energies
between 300 PeV and 1 EeV with the IceTop detector which was just recently nished
at the South Pole, as part of the IceCube neutrino observatory. IceTop is an array of
81 water Cherenkov tanks spread out over 1 square km. We also want to use IceTop as
an eective veto against charged particle background in the DeepCore array of IceCube,
embedded deep in the ice underneath IceTop.