We report experiments to determine the effect of radiation damage on the phonon spectra of the most common nuclear fuel, UO2. We have irradiated thin (∼ 300 nm) epitaxial films of UO2 with 2.1 MeV He2+ ions to 0.15 dpa and a lattice swelling of Δa/a ∼ 0.6 %, and then used grazing-incidence inelastic X-ray scattering to measure the phonon spectrum. We succeeded to observe the acoustic modes, both transverse and longitudinal, across the Brillouin zone. The phonon energies, in both the pristine and irradiated samples, are unchanged from those observed in bulk material. On the other hand, the phonon linewidths (inversely proportional to the phonon lifetimes), show a significant broadening when comparing the pristine and irradiated samples. This effect is shown to increase with phonon energy across the Brillouin zone. The decreases in the phonon lifetimes of the acoustic modes are roughly consistent with a 50 % reduction in the thermal conductivity.
@article{arxiv.1802.08593,
title = {Study of phonons in irradiated epitaxial thin films of UO$_2$},
author = {S. Rennie and E. Lawrence Bright and J. E. Darnbrough and L. Paolasini and A. Bosak and A. D. Smith and N. Mason and G. H. Lander and R. Springell},
journal= {arXiv preprint arXiv:1802.08593},
year = {2018}
}