Effect of ballistic damage in UO2 samples under ion beam irradiations studied by in situ Raman spectroscopy

The damage induced in uranium dioxide (UO2) during ion irradiation at low energy was studied by micro-Raman spectroscopy. Polycrystalline UO2 samples were irradiated by 0.9-MeV I, 2-MeV Au at 25 °C and by 4-MeV Kr ions at −160 °C in a wide range of fluences. In situ Raman measurements show similar spectra evolution no matter the ion beam used. The T2g band centred at 445 cm−1 related to the fluorine structure reveals a broadening with the irradiation damage increase. In addition, several bands ranging from 500 to 700 cm−1, which are attributed to sub- or sur-stoichiometric structural defects, are observed at the early stages of irradiation. Their intensities grow with the irradiation fluence to similar asymptotic relative values for all the irradiation conditions. The obtained Raman kinetics are compared with data from the literature on the microstructure evolution observed by Transmission Electronic Microscopy (TEM) and on the fraction of displaced atoms determined by Rutherford Backscattering Spectroscopy in channelling mode (RBS-C).