  As it was recently shown by Derishev etal (1999), initial GRB ejecta are
likely to contain comparable number of protons and neutrons. During
acceleration process, and/or later, due to interaction with external medium,
such ejecta are likely to be split into spatially distinct shells of neutron
and proton-electron plasmas. This leads to dynamical effects which can affect
the afterglow light curves. In this paper we study these effects including, for
the first time, radiation drag imposed on the neutron rich ejecta. In the
presence of efficient radiation drag and for typical ejecta Lorentz factor
(below 400), this is the neutron shell which moves faster and, after conversion
to proton-electron plasma, powers the afterglow. After certain amount of
deceleration, this shell is hit by the second one. Such collision will lead to
reflaring, as observed in some afterglow light curves.
