Study on effects of swift heavy ion irradiation in cerium dioxide using synchrotron radiation X-ray absorption spectroscopy

In order to simulate the effects of high energy fission products on high-burnup UO2 nuclear fuel pellets, CeO2 thin films and bulk specimens were irradiated with 200 MeV Xe ions. Effects of the irradiation were studied by using Extended X-ray Absorption Fine Structure (EXAFS) measurement and X-ray photoelectron spectroscopy (XPS) at synchrotron radiation facilities. The EXAFS spectra for the irradiated thin films near the Ce K-edge show the formation of the oxygen deficiency around Ce ions. XPS Spectra show that the valence state of Ce atoms is changed from intrinsic Ce4+ to Ce3+ state by the irradiation. As such irradiation effects appear even for low fluence irradiation, the experimental result suggests that the oxygen deficiency and the change in Ce valence state are due to high-density electronic excitation induced by the 200 MeV Xe ions.