  Silicon pixel detectors developed to meet LHC requirements were tested in a
beam at CERN in the framework of the ATLAS collaboration. The experimental
behaviour of irradiated and not-irradiated sensors in a magnetic field is
discussed. The measurement of the Lorentz angle for these sensors at different
operating conditions is presented. A simple model of the charge drift in
silicon before and after irradiation is presented. The good agreement between
the model predictions and the experimental results is shown.
