  We examine the prompt and afterglow emission within the context of the
Supercritical Pile model for GRBs. For this we have performed self-consistent
calculations, by solving three time-dependent kinetic equations for protons,
electrons and photons in addition to the usual mass and energy conservation
equations. We follow the evolution of the RBW as it sweeps up circumstellar
matter and assume that the swept-up electrons and protons have energies equal
to the Lorentz factor of the flow. While the electrons radiate their energies
through synchrotron and inverse Compton radiation on short timescales, the
protons, at least initially, start accumulating without any dissipation. As the
accumulated mass of relativistic protons increases, however, they can become
supercritical to the `proton-photon pair-production - synchrotron radiation'
network, and, as a consequence, they transfer explosively their stored energy
to secondary electron-positron pairs and radiation. This results in a burst
which has many features similar to the ones observed in GRB prompt emission. We
have included in our calculations the radiation drag force exerted on the flow
from the scattered radiation of the prompt emission on the circumstellar
material. We find that this can decelerate the flow on timescales which are
much faster than the ones related to the usual adiabatic/radiative ones. As a
result the emission exhibits a steep drop just after the prompt phase, in
agreement with the Swift afterglow observations.
