Upon X-ray irradiation, a number of glasses undergo a fluidization process: The atoms move from their original positions while keeping a similar distribution of interatomic distances, as for two snapshots of a liquid. This process has been studied looking at the atomic displacements over interatomic distances. We here extend these investigations to much longer length scales in the few nanometer range. For silica irradiated at doses of ∼5 GGy, our experiments clarify that this process is not characterized by the common atomic diffusion typical of liquids: It is rather the outcome of an atomic acceleration due to X-ray-induced local stresses random in both time and space, as in the famous example of stochastic acceleration of charged particles by interstellar fields.
Photo credits: Disordered Systems Group, University of Padova, 2023.