  The polarization of gamma ray emission scattered off the baryon rich material
that collimates a GRB fireball and the coasting speed of the irradiated matter
are calculated numerically for different geometries of the radiation source and
the collimating wall. It is shown that when the scattering material is Compton
sailing, the direction of maximum polarization is quite generally well within
the beaming cone of scattered radiation. As a result, the probability for
observing bright highly polarized GRB's increases considerably, provided the
Lorentz factor of the coasting matter is not well below 30, and the scattered
radiation is highly polarized even when the beam thickness is large compared to
$1/\Gamma$. It is suggested that correlation between polarization and intensity
could provide clues as to whether energy flows from matter to photons or the
reverse.
