Study on effects of swift heavy ion irradiation on the crystal structure in CeO2 doped with Gd2O3

To simulate the effects of Gd₂O₃-doping and high-energy fission products in UO₂, Gd₂O₃-doped CeO₂ pellets were irradiated with 200-MeV Xe¹⁴⁺ ions. Doping and irradiation effects were analyzed using X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS). The lattice constant of CeO₂ decreases and the local structure is disordered with increased doping levels. However, the irradiation induces an expansion of the lattice and a disordering of atomic arrangement near the Gd atoms. The effects of the irradiation become more pronounced with increasing Gd₂O₃-dopant levels. Our results are compared with those of a study involving Er₂O₃-doped CeO₂.     

Effects of swift heavy ion irradiation on the structure of Er2O3-doped CeO2

In order to simulate the effects of burnable poison doping on the fission fragment damage of UO₂ nuclear fuels, Er₂O₃-doped CeO₂ pellets were irradiated with 200 MeV Xe¹⁴⁺ ions. The irradiation effect was measured by means of X-ray diffraction (XRD). The expansion of lattice and the disordering of atomic arrangement due to the irradiation become more remarkable with increasing the concentration of the Er₂O₃ dopant.     

γ辐照联合H_2O_2处理污泥滤液的研究

采用60 Coγ射线辐照处理污泥滤液,通过对比处理前后化学需氧量(COD)、紫外可见吸光度和浑浊度的变化,研究了辐照处理中初始pH、初始H2O2浓度和吸收剂量对污泥滤液处理效果的影响。结果表明:在相同吸收剂量和初始H2O2浓度条件下,酸性条件更利于CODCr的降低;γ辐照联合H2O2处理存在显著协同效应,吸收剂量为18.75kGy、初始H2O2浓度为2mmol/L时,污泥滤液CODcr去除率达70.4%,浑浊度下降94.9%。     

Study of the magnetic modifications of Fe3O4 ferrite thin films induced by 2.03 GeV Kr ions irradiation

The effect of 2.03 GeV Kr²⁶⁺ ions irradiation on antiphase boundaries (APBs) of polycrystalline Fe₃O₄ ferrite thin films has been investigated. The structure, magnetic and electrical transport properties of samples were characterized. The initial crystallographic structure of the Fe₃O₄ remains unaffected after Kr-ion irradiation, but the magnetic and electrical transports properties are sensitive to swift heavy ions (SHI) irradiation and exhibit different behaviors depending on the Kr-ion fluence range. The energy deposition is mainly due to the electronic energy loss (S_e) and the large value of energy transferred induces an unusual density of defects, stress and heat annealing effect in the samples, which can affect on the arrangement of magnetic moments and APBs density strongly. On the basis of our observations we conclude that the production, accumulation and free of the defects and stress induced by SHI irradiation is more dominant in the case of the magnetic and electrical transport properties modifications of the Fe₃O₄ thin films.     

Recovery of neutron-irradiation-induced defects of Al2O3, Y2O3, and yttrium-aluminum garnet

SiC fiber-reinforced SiC matrix composites (SiC_f/SiC) are considered as one of the candidates for blanket materials in future fusion reactors and as an advanced fuel cladding material for next-generation fission reactors. Generally, the densification of SiC needs sintering additives and oxides such as Al₂O₃, Y₂O₃, and yttrium-aluminum garnet (YAG, Y₃Al₅O₁₂), which are frequently added to SiC. However, the effects of neutron irradiation on sintering additives are still unclear. In this study, we performed the neutron irradiation of Al₂O₃, Y₂O₃, and YAG at fluences up to 2.0–2.5 × 10²⁴ n/m² (E > 0.1 MeV) at 60–90 °C. The isochronal recovery of the macroscopic volume of Al₂O₃ against annealing temperature showed smooth and continuous shrinkage at a temperature of up to 1200 °C, and the volume slightly increased above that temperature. In contrast, the volume of Y₂O₃ showed quick shrinkage at the low temperature range, and slower and smooth recovery was observed up to ～1100 °C. In the case of YAG, the recovery of volume occurred in a step-wise manner at 600–750 °C, and continuous shrinkage occurred at temperatures lower and higher than that temperature range. The activation energies for the macroscopic volume recoveries of three oxides were obtained from the Arrhenius plots of the rate coefficients. Two-stage recovery was observed for Al₂O₃, whereas more complicated recovery processes were suggested for Y₂O₃ and YAG.     

Electronic sputtering of Gd3Ga5O12 and Y3Fe5O12 garnets: Yield, stoichiometry and comparison to track formation

The results of present paper have shown that sputtering of yttrium iron garnet (Y₃Fe₅O₁₂) under swift heavy ions in the electronic energy loss regime is non-stoichiometric. Here we are presenting additional experimental results for gadolinium gallium garnet (Gd₃Ga₅O₁₂) as target. The irradiations were performed with different ions (⁵⁰Cr (589 MeV), ⁸⁶Kr (195 MeV) and ¹⁸¹Ta (400 MeV)) impinging perpendicularly to the surface. As earlier, the sputtering yield was determined by collecting the emitted gadolinium and gallium atoms on a thin aluminium foil, placed upstream above the target and analyzing the Al catcher by Rutherford backscattering. Also for Gd₃Ga₅O_12, the emission of Gd and Ga is non-stoichiometric. Sputtering appears above a critical electronic stopping power of S_th = 11.6 ± 1.5 keV/nm, which is larger than the threshold for track formation, in agreement with other amorphisable materials. In addition, the angular distribution of the sputtered species was measured for Y₃Fe₅O₁₂ and Gd₃Ga₅O₁₂ using 200 MeV Au ions impinging the surface at 20° relatively to the surface. For the two garnets the ratio of Y/Fe (and Gd/Ga) varies with the angle of emitted species and the stoichiometry seems to be preserved only for an emission perpendicular to the surface.     

Electrical properties changes induced by electron radiation at TiO2/Si interface

TiO₂/Si structures were fabricated by electron beam evaporation, and exposed to electron beam irradiation to investigate their electrical properties using the high frequency capacitance-voltage measurements. It was found that samples annealed in oxygen became more radiation resistant than un-annealed samples, which can be explained by the Ti valence variations induced by radiation. The samples were characterized by X-ray diffraction to show the Ti₂O₃ crystalline phase transformed to anatase-crystalline phase after oxygen annealing.     

烧绿石(La1-yNdy)2Zr2O7模拟固化241Am的晶体结构稳定性研究

为研究²⁴¹Am在La₂Zr₂O₇烧绿石中的固化行为及其对烧绿石晶体结构稳定性的影响,实验选用Nd作为²⁴¹Am的模拟物,采用Sol-喷雾热解法合成了(La_1-yNd_y)₂Zr₂O₇（0.0≤y≤1.0）系列样品,并借助X射线衍射和振动光谱手段对样品的晶体结构稳定性进行了研究。实验结果表明：随着Nd掺杂量的增加,O48f位置参数x_48f和I₍₁₁₁₎ /I₍₂₂₂₎均呈规律性增大,Raman谱逐渐展宽,IR谱发生蓝移,所有结果均证实用Nd不断替换La将导致烧绿石晶体结构有序化程度逐渐降低。另外,实验发现掺杂量y≈0.8是烧绿石晶体结构发生几何相变的逾渗阈值,超过该阈值有序的烧绿石结构将发生突变进而加速向无序萤石结构转变,该实验结果可为(La_1-yAm_y)2Zr2O7固溶体的结构稳定性研究提供参考。     

Ion-induced mixing at Nb/Fe2O3 interface studied by CEMS technique

Conversion electron Mössbauer spectroscopy (CEMS) was used to study the interface behavior between Nb and Fe₂O₃ layers. The interfacial reaction between Nb and Fe₂O₃ was enhanced by argon ion irradiation and the rupture of Fe-O bonding caused by irradiation was also observed. The correlation between the Fe-O bonding energy calculated via Molecular Orbital theory and irradiation induced ionization at the Nb/Fe₂O₃ interface was established to explain the observed phenomena. The subsequent thermal annealing of the irradiated bilayers led to the interdiffusion between Nb and free Fe precipitated from the oxide, with an Fe-Nb phase of ferromagnetic character possibly forming at the interface region.     

Al2O3-containing silver phosphate glasses as hosting matrices for radioactive iodine

Al₂O₃-containing silver phosphate glasses were synthesized to investigate the feasibility of phosphate glasses for the immobilization of radioactive iodine (¹²⁹I) present in spent nuclear fuel. Characterizations were performed by X-ray diffraction, Fourier transformed infrared spectroscopy, and scanning electron microscopy coupled with energy dispersive spectroscopy to examine structures, bonding properties, surface morphology, and elemental distribution of the synthesized glasses. The principal results showed that iodine became more strongly immobilized in the phosphate glasses with the addition of Al₂O₃, which was confirmed by the decrease of iodine leaching rates with approximately one order of magnitude. The present study would be helpful to decide whether Al₂O₃-containing silver phosphate glasses could be used as a candidate matrix to incorporate ¹²⁹I.     

Nanoparticles of Al2O3:Cr as a sensitive thermoluminescent material for high exposures of gamma rays irradiations

Aluminum Oxide (Al₂O₃) doped with proper activators is a highly sensitive phosphor commonly used for radiation dosimetry using thermoluminescence (TL) technique. Nanoparticles of this material activated with Chromium (Cr) have been synthesized using the propellant chemical combustion technique and studied for their TL response. They were characterized by X-ray diffraction and scanning electron microscope. The synthesized material has spherical nanoparticles with grain size around 25 nm. These nanoparticles were exposed to heavy doses from γ-rays of ¹³⁷Cs. The TL glow curves show a prominent peak at around 474 K. This peak is found to be sensitive for high exposures of γ-rays and has linear response in the range of 100 Gy-20 kGy without showing saturation. This remarkable result suggests that Al₂O₃:Cr nanoparticles might be used for the dosimetry of food and seed irradiations.     

Effect of additive ions on the optical density and stability of the color centers induced by X-ray irradiation in soda-lime silicate glass

To apply radiation-induced coloration of glasses as a reversible glass-coloring technique, we studied the influence of various additive ions incorporated into a soda-lime silicate glass on the optical density and stability of the color induced by X-ray irradiation. Absorption spectra before and after irradiation are discussed in the comparison with those of the undoped soda-lime silicate glass. Additive ions were incorporated as metal oxides, namely TiO₂, V₂O₅, Fe₂O₃, ZnO, Ga₂O₃, GeO₂, ZrO₂, Nb₂O₃, MoO₃, Ag₂O, In₂O₃, SnO, SnO₂, CeO₂, Eu₂O₃, Ta₂O₅, WO₃ and Bi₂O₃. Among them, TiO₂, GeO₂, Nb₂O₃, MoO₃, Ag₂O, In₂O₃, Eu₂O₃, Ta₂O₅, WO₃ and Bi₂O₃ have a large effect on optical density. The optical densities in the visible region for glasses doped with these oxides were much stronger than for undoped soda-lime silicate glass. On the other hand, incorporation of Fe₂O₃, SnO and CeO₂ reduced the optical density. Over longer periods the coloration of the undoped glass was one of the most stable while those of the Fe₂O₃, SnO and CeO₂-doped glasses soon faded.     

Improvement of UO2 Pellet Properties by Controlling the Powder Morphology of Recycled U3O8 Powder

Powder morphology evolution of recycled U₃O₈ according to the thermal treatments has been studied. The defective UO₂ pellets are oxidized to U₃O₈ powders at a conventional temperature of 350 or 450°C in air. Those powders are pressed into green pellets and then sintered at 1,500 and 1,730°C in H₂ gas flow. Final reoxidized U₃O₈ powers are obtained by reoxidizing those sintered pellets at 450°C in air. This paper shows that the reoxidized U₃O₈ powder morphology and the BET surface areas are greatly dependent on the density of sintered UO₂ pellets before reoxidation. Reoxidized U₃O₈ powders are added to virgin UO₂ powders to fabricate UO₂ pellets and the effect of such addition on the UO₂ pellet properties is investigated. The reoxidized U₃O₈ powders having a certain range of BET surface area significantly promote the grain growth of UO₂ pellets.     

Treatment of UO2 pellets used for preparing fuel elements of HTR-10 followed by supercritical fluid extraction

International interest in high temperature gas-cooled reactor (HTGR) has been increasing in recent years. It is important to study on reprocessing of spent nuclear fuel from HTGR for recovery of nuclear resource and reduction of nuclear waste. Treatment of UO₂ pellets used for preparing fuel elements of the 10 MW high temperature gas-cooled reactor (HTR-10) followed by supercritical fluid extraction was investigated. When UO₂ pellets were dissolved and extracted with tri-n-butyl phosphate (TBP)–HNO₃ complex in supercritical CO₂ (SC-CO₂), the extraction efficiency was less than 7% under experimental conditions. After UO₂ pellets were ground into UO₂ fine powders, the extraction efficiency of the UO₂ fine powders with TBP–HNO₃ complex in SC-CO₂ could reach 92%. After UO₂ pellets broke spontaneously into U₃O₈ powders under O₂ flow and 600 °C, the extraction efficiency of the U₃O₈ powder with TBP–HNO₃ complex in SC-CO₂ could reach more than 98%.     

Thermal conductivity of Na2O–B2O3–SiO2 melts

Borosilicate glasses are candidate materials for the immobilization of high-level radioactive waste. The values of thermal conductivity of different borosilicate melts are thus indispensable information when optimizing the temperature distribution in a glass melting furnace. In this study, the thermal effusivity of Na₂O–B₂O₃–SiO₂ melts was measured using a front heating–front detection laser-flash method. The thermal conductivity, which can be obtained by combining the measured thermal effusivity with the specific heat capacity and density, was calculated using the least-squares method; the values for the Na₂O–B₂O₃–SiO₂ melts either slightly decreased linearly with increasing temperature or remained almost constant over the investigated temperature range. The values of thermal conductivity of the Na₂O–B₂O₃–SiO₂ melts were higher than those of B₂O₃–SiO₂ melts and lower than those of CaO–B₂O₃–SiO₂ melts. Furthermore, the thermal conductivity of the Na₂O–B₂O₃–SiO₂ melts was compared with those of the B₂O₃–SiO₂ and CaO–B₂O₃–SiO₂ samples.     

Effects of Mg-ion implantation in α-Al2O3 and α-Al2O3:Mg crystals: Electrical conductivity and electronic structure changes

Undoped and Mg-doped α-Al₂O₃ single crystals were implanted with Mg ions, with an energy of 90 keV and a fluence of 10¹⁷ ions/cm². DC electrical measurements using the four-point probe method, between 295 and 428 K, were used to characterize the electrical conductivity of the implanted area. Measurements in this temperature range indicate that the electrical conductivity after implantation is thermally activated with an activation energy of about 0.03 eV both in undoped and in reduced Mg-doped α-Al₂O₃ crystals, whereas the activation energy in oxidized Mg-doped α-Al₂O₃ crystals remains close to that before implantation. The I-V characteristics of the latter samples reveal a blocking behavior of the electrical contacts on the implanted area in contrast to the ohmic contacts observed in α-Al₂O₃ single crystals with the c-axis perpendicular to the broad face, where the Mg ions were implanted. We conclude that the enhancement in conductivity observed in the implanted regions is related to the intrinsic defects created by the implantation, rather than to the implanted Mg ions. The relationship between the oxygen vacancy concentrations at different stages of etching and the changes in the electronic structure, the chemical bonding, and the Al³⁺(2p)/O²⁻(1s) and Mg²⁺(1s)/O²⁻(1s) relative intensities was studied by X-ray Photoemission Spectroscopy.     

Ion beam analysis of partial lithium extraction of LiMn2O4 by chemical delithiation

Lithium manganese oxide, LiMn₂O₄, has been studied by many research groups. This material is a great candidate to be used as positive electrode in rechargeable lithium-ion batteries because of its low cost, abundant precursors and non-toxicity. LiMn₂O₄ has a spinel Fd-3m structure and shows a reversible extraction and insertion of lithium ions that is one of the most important characteristic of positive electrodes in rechargeable batteries.In this work, LiMn₂O₄ samples were synthesized by solid state reaction. A partial lithium removal was performed on this system by chemical delithiation using HCl aqueous solutions at different concentrations. Six partial-extracted compounds were obtained and characterized by Ion beam analysis (IBA) in order to obtain the Li concentrations. X-ray diffraction (XRD) and Rietveld analyses were also performed. A rigorous study of lithium contents is critical to analyze the structure properties of these compounds and samples production parameters. The IBA method used in this work was the analysis of energy spectra of elastic backscattered (EBS) proton from Mn, O and Li nuclei and the α-particles energy from the ⁷Li(p,α)⁴He nuclear reaction (NR).     

Growth Mechanism of Voids in Fast Reactor Irradiated Austenitic Stainless Steel

The γ-radiolysis of water has been studied using a water-loop specially designed for this purpose. The water was circulated without contact with air during the irradiation. The apparent G(H₂) value was found to be roughly 10-³. However a corresponding amount of O₂ was not found, due to its comsumption by corroding reactions of the constituent materials under radiation field. In the presence of O₂ and H₂O₂, the H₂-yield curves vs. the irradiation dose were revealed a very distinctive characteristic: following a rapid increase with initial irradiation a plateau range has appeared. The H₂-yield at this plateau range depended on the initial concentration of additives. Continued irradiation, however, caused a gradual further rise in the H₂-yield above the plateau value at a rate corresponding to that found in the pure water system. These yield curves are discussed on the basis of the free radical model for the radiolysis of water.     

Oxidation of Uranium Dioxide

The oxidation of UO₂ was studied by thermogravimetry and X-ray diffraction. It was clarified that the thermal history covering the first stage of the oxidation from UO₂ to U₃O UO₇ significantly influenced the rate of the oxidation of the second stage from U₃O₇ to U₃ O₈.

The entire oxidation reaction proceeded in what to all appearances, was a single stage when the specimen temperature was raised rapidly, whereas at slower rates of heating up, two distinct stages of oxidation were observed, separated by an intermediate induction period. These findings suggest the existence of a close connection between the rate of formation of the U₃O₇ phase and the rate of the subsequent oxidation of this phase: A slow formation of U₃O₇ would tend to prolong the induction period preceding the second stage of the oxidation. A similar effect was observed also with annealing of the intermediate U₃O₇ at 200°C: The increase of annealing time prolonged the induction stage.

The rate of the second stage oxidation was fairly well expressed by Johnson & Mehl's equation, log (1/(1-y/)=(1/2.303)kⁿtⁿ . The time exponent n in this equation varied in the range of 1.0~2.5, and the rate constant k of 1.15×10^?4~2.04 ×10^?1 min^?1, depending on the experimental conditions.     

Ion guiding through capillaries in uncoated Al2O3 membranes

We made an experimental study on ion guiding through capillaries in uncoated Al₂O₃ membranes using a variety of ions such as O¹⁺, O³⁺, and O⁶⁺. The incident energy was varied within the range of 30-150 keV. The results were compared with others using coated PET and Al₂O₃ capillary membranes as well as with the so-called scaling law discovered by Stolterfoht and his co-workers. Good agreement of our results with the scaling law was found. However, our membranes showed extraordinarily strong guiding ability. The reason lies in that our membranes were uncoated. A slower charge drift speed along the insulating capillary wall and a much larger equilibrium charge Q_∞ seems to exist in our experiment.