  The collective nature of light interactions with atomic and nuclear ensembles
yields the fascinating phenomena of superradiance and radiation trapping. We
study the interaction of gamma rays with a coherently vibrating periodic array
of two-level nuclei. Such nuclear motion can be generated, e.g., in ionic
crystals illuminated by a strong driving optical laser field. We find that
deflection of the incident gamma beam into the Bragg angle can be switched on
and off by nuclear vibrations on a superradiant time scale determined by the
collective nuclear frequency, which is of the order of terahertz. Namely, if
the incident gamma wave is detuned from the nuclear transition by much larger
frequency it passes through the static nuclear array. However, if the nuclei
vibrate with the frequency of the gamma ray detuning then parametric resonance
can yield energy transfer into the Bragg deflected beam on the superradiant
time scale, which can be used for fast control of gamma rays.
