  Protoplanetary disks, interstellar clouds, and active galactic nuclei,
contain X-ray dominated regions. X-rays interact with the dust and gas present
in such environments. While a few laboratory X-ray irradiation experiments have
been performed on ices, X-ray irradiation experiments on bare cosmic dust
analogs have been scarce up to now. Our goal is to study the effects of hard
X-rays on cosmic dust analogs via in-situ X-ray diffraction. By using a hard
X-ray synchrotron nanobeam, we seek to simulate cumulative X-ray exposure on
dust grains during their lifetime in these astrophysical environments, and
provide an upper limit on the effect of hard X-rays on dust grain structure.
  We prepared enstatite nanograins, analogs to cosmic silicates, via the
melting-quenching technique. These amorphous grains were then annealed to
obtain polycrystalline grains. These were characterized via scanning electron
microscopy and high-resolution transmission electron microscopy before
irradiation. Powder samples were prepared in X-ray transparent substrates and
were irradiated with hard X-rays nanobeams (29.4 keV) provided by beamline
ID16B of the European Synchrotron Radiation Facility. X-ray diffraction images
were recorded in transmission mode. We detected the amorphization of
polycrystalline silicates embedded in an organic matrix after an accumulated
X-ray exposure of 6.4 x 10$^{27}$ eV cm$^{-2}$. Pure crystalline silicate
grains (without resin) did not exhibit amorphization. None of the amorphous
silicate samples (pure and embedded in resin) underwent crystallization. We
analyzed the evolution of the polycrystalline sample embedded in an organic
matrix as a function of X-ray exposure. Loss of diffraction peak intensity,
peak broadening, and the disappearance of discrete spots and arcs, revealed the
amorphization of the resin embedded (originally polycrystalline) silicate
sample.
