  The production of energetic (multi-GeV) heavy ion beams by acceleration of
ultra-thin foils through the application of radiation pressure to a
self-generated, imperfect plasma mirror (photon absorption probability {\eta}
finite) is studied. To evaluate the foil dynamics a relativistic model was
developed for a constant and relativistic invariant value of the
phenomenological parameter {\eta}. The achievable efficiency of kinetic energy
transfer to the matter has been evaluated as function of the parameters
involved ({\eta}, the aimed average foil velocity in unit of the light speed
{\beta}, etc.). The expected collimation degree for the generated ion beams,
the associated energy range, the self-consistency of the model in view of the
{\eta} finite value and the survival to R-T instability were evaluated for
initially thin material disks.
