Wave vector dependence of x-ray beam induced dynamics in sodium silicate glasses

We have probed the atomic dynamics of two sodium silicate glasses in a wide wave vector range by means of x-ray photon correlation spectroscopy. The wide angle setup has been modified to cover a $Q$ range that extends to small angles, close to the range normally covered by the usual small-angle x-ray scattering configuration. During irradiation, the oxide samples undergo a transformation to a new amorphous state with different structural and dynamical properties. The observed dynamics before and after the structural transformation shows the presence of de Gennes narrowing. In the low wave vector region, the dynamics is affected by a ballisticlike motion at low absorbed doses, while the glass obtained after prolonged irradiation has a $Q$-independent relaxation time. This observation strengthens the interpretation of the new amorphous phase as a rejuvenated glass that lies in a higher-energy region of the potential landscape.