Geomagnetic storms are responsible for the large increase of trapped electron fluxes in the magnetosphere resulting in the formation of radiation belts. Such belts can also be artificially produced by injection of electron beams. The dynamic evolution of the electron fluxes is very important for satellite protection purpose. Up to now most of the existing studies have been restricted to the stationary description of natural radiation belts. Recently, great effort has been made for their dynamic description [Bourdarie et al., 1996>. We have developed a numerical code, which is able to follow the time behavior of the electron population under influence of collisions with tenuous atmosphere and resonant scattering by plasma waves. The code solves the phase-averaged Fokker-Planck equation of the electron momentum distribution function on magnetic shells within the Earth's inner magnetosphere. The physical arguments incorporated in the code include phase-averaged, approximate collision operators and quasi-linear diffusion due to resonant interaction with whistler plasma waves. The magnetic field is supposed to be tilted and decentered. Numerical experiments to simulate the decay and particles' loss in an artificial Van Allen belt are presented, and comparisons with available published data are discussed to validate the code [Abel and Thorne, 1998>. ¿ 2001 American Geophysical Union