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Nuclear Science User Facilities 122 In this experimentwere learning that identifying the differences between oxygen doping and irradiation isnt so simple.There may even be differences between the proton- and He-irradiated materialsand we want to make sure we get it right. Steve ConradsonBeamline ResponsibleSynchrotron SOLEIL current position Figure 2. k3 R EXAFS of Ref UO2 UO2 irradiated to 0.006 dpa with He2 ions and UO2 irradiated to 0.035 dpa with He2 ions. Plots 1-3 the modulus of the real part of the transform of both data and fit. Insets top k3 spectra overlaid with curve-fit bottom moduli of the data fit difference between data and fit and the individual contributions to the fit inverted for clarity. Plot 4 modulus of the Fourier transforms of the k3 -weighted EXAFS spectra of indicated samples. Transforms were performed over a range of 2.70 to 14.75 -1 . 1 m. He-implanted samples irradi- ated to 0.0060.035 displacements per atom dpa and proton-irradiated samples 0.010.5 dpa were also successfully studied using EXAFS at SSRL.This was a first-of-its-kind demonstration of -EXAFS measure- ments on FIB lamellae and brought together high-energy x-ray studies from synchrotron sources and the microscopic analysis techniques used in material characterization. EXAFS analysis has shown that irradia- tion disrupts local structure by giving rise to multisite oxygen distribution at approximately 1.9 angstroms from the absorbing atom which is 0.2 farther than in documented UO2x .This is similar to oxygen interstitials created in UO2x however there is no observed oxidation of the material.The multisite distribution results from uranyl-type bonds that are 1.8 in length and extremely stable due to their oblate geometry which causes them to distort the original local structure. The EXAFS data from the irradiated UO2 shows a consistent decrease in amplitude in the crystallographic shells as irradiation doses increase longer bond distances between near neighbors and the appearance and increase of a shoulder on the low R side at 1.9 of the first crystal- lographic U-O shell. Random disorder in the material would result in a significant loss of amplitude and addi- tional loss of overall structure which is not seen in this set of samples. Due to the consistent amplitude reduction as shown in Figure 2 it can be theo- rized that the defects are not random but instead cluster in such a way that the overall lattice retains its UO2 struc- ture even at higher irradiation doses. This is consistent with several studies that indicate fluorite ceramics in a reactor maintain their lattice structure even at high irradiation doses.