Irradiated CeO2 Research Articles

Understanding the dose-rate effect on loop characteristics in Kr+-irradiated CeO2 by in-situ TEM study

Irradiation of CeO2 with heavy ions is commonly used to accelerate the evaluation of the irradiation performance of UO2 nuclear fuel. However, the differences in damage rates between ions and neutrons have led to doubts about this method, making it especially important to study the dose rate effect. Here, two kinds of dose rates were used to in-situ irradiate CeO2 using 400 keV Kr+ at 550 °C and 700 °C to study the dose rate effect on loop characteristics. High dose rate (HR) led to low-density and small-sized dislocation loops compared to low dose rate (LR), which was attributed to the initial high concentration of oxygen vacancies and enhanced recombination of point defects. HR was found to promote the direct nucleation of perfect dislocation loops (PDLs), while under LR irradiation, the PDLs tended to be formed by the transformation of Frank dislocation loops (FDLs) through a typical unfaulting. At a same dose, the proportion of PDL under the HR condition was much higher than that under the LR condition. Temperature greatly affected the loop characteristics. High temperature caused large-sized and small dense loops, as well as high PDL proportion. Moreover, the newly nucleated PDL tended to be close to the pre-existing PDLs and had the same Burgers vector as the adjacent PDL under HR irradiation at 700 °C. Current results provide underlying insights for assessing the effect of dose rate on irradiation-induced loop evolution and a reference for understanding the dose rate effect.

Crack formation and optical properties in 175 MeV Au13+ ion beam irradiated CeO2 thin films

CeO2 thin films have been deposited on fused silica substrates using RF-sputtering technique. 175 MeV Au13+ ions beam with two different fluences, 1 × 1012 ions/cm2 and 5 × 1012 ions/cm2, have been applied to modify the structural, surface and optical properties of CeO2 thin films. X-ray diffraction (XRD), atomic force microscopy (AFM), UV–visible absorption and photoluminescence (PL) measurements have been performed to investigate the 175 MeV Au13+ ion-irradiation induced changes in CeO2 thin films. The irradiated films show the formation of nanocrystalline granulizes on the film surface. The mud like cracks have been evolved at the ion-fluence of 5 × 1012 ion/cm2. The modifications in the optical and structural properties and the formation of cracks have been studied under the light of 175 MeV Au13+ ion irradiation and energy loss process into CeO2 lattice.

Microstructure evolution in 200-MeV Xe ion irradiated CeO2 doped with Gd2O3

The microstructure of virgin and heavy ion-irradiated Ce1–xGdxO2–x/2 with a wide range of Gd dopant concentrations (0 ≤ xGd ≤ 0.5) was evaluated by x-ray diffraction (XRD), micro-Raman spectroscopy, and transmission electron microscopy (TEM) for selected area electron diffraction (SAED) analysis and plane-view bright-field (BF) imaging of ion tracks. The Ce1–xGdxO2–x/2 samples were irradiated with 200-MeV Xe14+ ions up to fluences from 3 × 1011 to 1 × 1013 cm−2 at ambient temperature. XRD patterns of the virgin Ce1–xGdxO2–x/2 samples showed saturation of lattice parameter and relaxation of microstrain in Ce1–xGdxO2–x/2 which are attributed to the increasing Gd concentration. Moreover, micro-Raman spectroscopy and SAED patterns revealed the bixbyite (C-type) structure formation and oxygen vacancy ordering for xGd > 0.2 that is induced by dispersed C-type domains in the fluorite-structured (F-type) matrix. In the irradiated samples, asymmetric XRD peaks induced by lattice distortion were observed together with ion tracks in BF-TEM images. The radiation damage was recovered with the increase of Gd concentration. There is a rapid reduction of radiation damage cross section for xGd > 0.2 with a reduction of the C-type structure reflections in XRD and SAED patterns.

Tailoring of defects dependent magnetic properties of swift heavy ion irradiated CeO2 for spintronics application

The present investigation reports the swift heavy ion induced effects on cerium oxide (CeO2) thin films. These thin films were deposited on Si (111) substrates by the electron-beam evaporation method and irradiated by a 100 MeV O7+ ion beam with different ion fluences. X-ray diffraction analysis of these films confirms the stable fluorite phase of CeO2 even after the higher fluence of irradiations. Raman measurement also supports the presence of the F2g phase of CeO2 and the presence of defect states. The Gaussian deconvolution of photoluminescence (PL) spectra reveals various defect-associated peaks. The broad peaks in the PL spectra are associated with oxygen vacancies and are red-shifted (494–520 nm) with ion fluences. The surface morphological images show the modification in the surface roughness with ion irradiation and the re-growth of smaller circular-formed nanoparticles on the surface is observed at the fluence of 5 × 1011 ions/cm2. Magnetic measurements show an enhancement in magnetic ordering with ion irradiation. All the samples demonstrate room temperature ferromagnetism with magnetic saturation (Ms) up to 14.57 emu/cm3. The saturation magnetization in irradiated thin films is directly correlated to the area under the peak of defect-associated PL emission. The mechanism such as the oxygen vacancy-based F-center exchange model is considered to understand the enhancement of ferromagnetism in ion irradiated CeO2 thin films. Some popular theoretical models are also employed to determine various magnetic parameters.

Influence of thermal effect on dislocation loop evolution in Fe+-irradiated CeO2 during in-situ annealing

Cerium dioxide (CeO2) is widely used as a surrogate fuel for uranium dioxide (UO2) because of their same cubic fluorite crystal structure, nearly identical lattice parameters and similar physical properties. The degree of irradiation damage is related not only to the irradiation dose but also to the thermal effect. The influence of the thermal effect on the microstructure of Fe+-irradiated CeO2 was investigated using in-situ transmission electron microscopy analysis during annealing. Shrinkage of the dislocation loops was observed for the first time in the irradiated CeO2 foil. The threshold size determining whether the dislocation loop shrank was found to be approximately 19 nm through experimental measurements. When the loop size was less than this value, the dislocation loop shrank or even disappeared as the annealing time increased. Moreover, the smaller the loop size, the larger the shrinkage. The shrinkage rate measured in the in-situ annealing experiment was approximately 0.08 nm/s, which was almost consistent with the theoretical calculation (about 0.11 nm/s). However, when the loop size was larger than 19 nm, the loop grew rapidly at the beginning of annealing and then remained stable.

Phase stability of pre‐irradiated CeO2 with swift heavy ions under high pressure up to 45 GPa

AbstractThe effect of defects on the high‐pressure behavior of materials is fundamental to understanding and designing materials for extreme environments. Previous work has demonstrated that radiation damage can enhance phase stability or alter the transformation pathway. Here, we report the high‐pressure phase stability of CeO2 irradiated by swift heavy ions. CeO2 is of particular interest because it can be used as a non‐radioactive surrogate for UO2 and PuO2. High‐pressure Raman spectroscopy shows that low‐fluence ion irradiated CeO2 exhibits nearly the same high‐pressure behavior as unirradiated CeO2; whereas, after high‐fluence irradiation, the phase stability of CeO2 is significantly enhanced, with the critical phase transition pressure increased from 31.7 to 37.3 GPa and only about 7% high‐pressure phase transition fraction at 45.1 GPa. In comparison with the high‐pressure Raman results of pre‐irradiated CeO2 before and after 573, 1073, and 1 273 K annealing in air, we propose that large interstitial‐type defect clusters, such as dislocation loops formed in heavily‐irradiated CeO2, are predominately responsible for the increased phase stability at high pressures.

Grain size effects on irradiated CeO2, ThO2, and UO2

Microcrystalline and nanocrystalline UO2, ThO2, and CeO2 (∼2 μm and∼20 nm particle size, respectively) were irradiated with 946 MeV Au ions at room temperature and characterized by synchrotron X-ray diffraction, Raman spectroscopy, and transmission electron microscopy. All samples show a small increase in unit cell parameter as a function of ion fluence (0.17 ± 0.03% for CeO2 and 0.11 ± 0.03% for ThO2), except microcrystalline UO2, which displays a small contraction of the unit cell (−0.06 ± 0.02%). Raman spectroscopy measurements of microcrystalline UO2 indicate an increase in nonstoichiometry after irradiation. All bulk materials are subject to an increase in heterogeneous microstrain, most notably UO2, implying that the relatively small changes in unit cell parameter are accompanied by substantial local disorder induced by isolated defects. The magnitude of volumetric swelling for all materials is larger in the nanocrystalline form as compared with the microcrystalline form (0.38 ± 0.60% for CeO2, 0.14 ± 0.03% for ThO2, and 0.52 ± 0.13% for UO2). ThO2 shows the smallest difference in swelling between the microcrystalline and nanocrystalline samples (∼0.03%). All nanocrystalline materials exhibit irradiation-induced grain coarsening along with a decrease in heterogeneous microstrain with increasing ion fluence, except nanocrystalline CeO2, which shows no observable change in grain size and a slight increase in heterogeneous microstrain attributed to the accelerated formation of a secondary Ce11O20 phase evidenced in the X-ray diffraction data, present in both nanocrystalline and microcrystalline materials. Surprisingly, nanocrystalline UO2 exhibits a significant degree of swelling indicative of a decrease in oxygen content along with an increase in disorder induced by oxygen loss at grain boundaries during irradiation, based on the analysis of X-ray diffraction and Raman spectroscopy.

Effect of electron beam irradiation on the magnetic, thermal and luminescence properties of various oxide metal nanopowders

Magnetic nanopowders of oxides Al2O3, SiO2, CeO2 and YSZ (ZrO2-8% Y2O3) with a high specific surface area irradiated in air by electrons with energy of 700 keV, pulse duration 100 ns, using the repetitively pulsed accelerator URT-1 within 15 and 30 min. The magnetic, thermal, and cathode luminescence characteristics of NPs were measured before and after irradiation. It was established that the electron irradiation non-monotonically changes the magnetization of the pristine samples. On the contrary, a clear correlation between the intensity of cathode luminescence and the irradiation dose is found in the most of the oxides. Thermal stability and phase transformations of unirradiated and irradiated CeO2 and YSZ oxides were analyzed with the aid of synchronous analysis, using the methods of thermogravimetry and differential scanning calorimetry. The luminescent and thermal properties reflect the transformation of structural defects in NPs more strongly after exposure to a pulsed electron beam in comparison with corresponding changes of the NP's magnetic response.

Optical, FT infrared and photoluminescence spectra of CeO2 – doped Na2O – ZnO – B2O3 host glass and effects of gamma irradiation

Collective optical, FTIR and photoluminescence spectra of prepared (1 → 10) CeO2 doped Na2O – ZnO – B2O3 glasses have been examined before and after gamma irradiation doses 2 or 9 × 104 Gy (2 or 9 Mrad). Optical absorption spectrum of undoped glass reveals distinct UV absorption bands which are correlated with trace impurities of ferric ions. Upon gamma irradiation, the UV bands reveal limited changes accompanied with the generation of an induced visible band which is assumed to be due to (BOHC) or (NBOHC). The CeO2 – doped glasses show an additional UV band due to Ce3+ ions while the absorption for Ce4+ ions are assumed to be overlapped by the strong charge transfer absorption due to traces impurities of Fe3+ ions. The irradiated CeO2 – doped glasses reveal no induced visible band due to the efficiency of cerium ions to capture electrons and positive holes during the irradiation. The CeO2 – doped glasses show a distinct luminescence peak centered at 410 nm after excitation at 308 nm and its intensity increases with the CeO2. The optical parameters of the band gap energy and Urbach energy are found to change with the CeO2 content. FTIR spectra of the undoped and CeO2 – doped glasses are almost similar with minor variations in the intensities of some vibrational bands and they show vibrational modes due to both triangular and tetrahedral borate groups in their specific different wavenumbers. The IR spectra of the irradiated glasses reveal stability with minor variations in the intensities of some bands.

Optical Properties Characterization of Gamma Irradiated CeO2 Nanoparticles Solution

Optical properties of CeO2 nanoparticles solution have been studied to explore the possibility of CeO2 nanoparticles as a liquid chemical dosimeter to measure gamma radiation in radiotherapy. CeO2 nanoparticles were synthesized by ultrasound irradiation of cerium nitrate solution. The CeO2 nanoparticles were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). CeO2 nanoparticles solution with concentration of 2.5 x 10-4 g/ml was irradiated by 1.3 MV 60Co gamma rays with a dose of 1.0 to 2.5 Gy. The UV absorbance spectrum of unirradiated and irradiated CeO2 nanoparticles solution was measured by using UV-Vis spectrophotometer. The UV absorbance of CeO2 nanoparticles solution increased with increasing radiation dose and caused a change in the band gap. The change in optical properties of CeO2 nanoparticles solution is correlated to chemical reactions induced by gamma radiation. The obtained chemical yield was in the order of 103 mol/J indicates the sensitivity of CeO2 nanoparticles to gamma radiation. The results show the possibility of CeO2 nanoparticles for use as gamma radiation dosimeter.

The effect of fission-energy Xe ion irradiation on the structural integrity and dissolution of the CeO2 matrix

This work considers the effect of fission fragment damage on the structural integrity and dissolution of the CeO2 matrix in water, as a simulant for the UO2 matrix of spent nuclear fuel. For this purpose, thin films of CeO2 on Si substrates were produced and irradiated by 92 MeV 129Xe23+ ions to a fluence of 4.8 × 1015 ions/cm2 to simulate fission damage that occurs within nuclear fuels along with bulk CeO2 samples. The irradiated and unirradiated samples were characterised and a static batch dissolution experiment was conducted to study the effect of the induced irradiation damage on dissolution of the CeO2 matrix. Complex restructuring took place in the irradiated films and the irradiated samples showed an increase in the amount of dissolved cerium, as compared to the corresponding unirradiated samples. Secondary phases were also observed on the surface of the irradiated CeO2 films after the dissolution experiment.

Effects of high-energy heavy ion irradiation on the crystal structure in CeO2 thin films

We studied the change in crystal structure of 200MeV Xe and 10MeV I ion irradiated CeO2 thin films by means of X-ray diffraction (XRD). The experimental result showed that the average lattice parameter of CeO2 decreased and the full width at half maximum increased by the ion irradiation. Their changes are well correlated with the electronic stopping powers for I and Xe ions. The dependence of lattice parameter on the electronic energy loss was analyzed by using the Poisson’s law, and the radii of the regions affected by the irradiation were determined.

Separation of carrier free152, 153Dy and151–153Tb from16O7+ irradiated CeO2 by liquid-liquid extraction

Charged particle activation of natural CeO2 with ≈80 MeV16O7+ results in the formation of carrier free isotopes,151, 152, 153Dy and their daughter products,151, 152, 153Tb, in the matrix. The liquid cation exchanger HDEHP, has effectively been utilised as an extractant in the quantitative separation of the activation products namely151, 152, 153Dy,151, 152, 153Tb from the bulk target matrix of ceric oxide.