X-ray study of radiation damage in UO2 irradiated with high-energy heavy ions

In order to characterize the radiation damage due to ion-track formation in UO2, polycrystalline samples have been irradiated with 210 MeV Xe ions, and characterized with X-ray diffraction technique and with extended X-ray absorption fine structure (EXAFS) technique using X-ray near U L3-edge. The result of the XRD measurement shows that the change in XRD profile is observed at relatively low fluence of 1016 ions/m2, where the ion-tracks should occupy about 20% of the sample when the typical diameter of 5 nm is assumed. The damages detected by XRD increase monotonically with increasing fluence up to relatively high fluence of 1019 ions/m2. The irradiation-induced change in EXAFS spectra near U L3-edge is not observed in UO2 irradiated with 210 MeV Xe ions at highest fluence of 1019 ions/m2. The failure of the damage detection in EXAFS spectra may be due to a deep penetration of high-energy X-ray, which results in smearing of the signal from the damaged shallow region. The depth profile of X-ray penetration may critically affect the detection efficiency of the damage introduced by energetic ion irradiation.