MeV Xe Ions Research Articles

The Influence of Grain Size on Microstructure Evolution in CeO2 under Xenon Ion Irradiation.

Large-grained UO2 is considered a potential accident-tolerant fuel (ATF) due to its superior fission gas retention capabilities. Irradiation experiments for cerium dioxide (CeO2), used as a surrogate fuel, is a common approach for evaluating the performance of UO2. In this work, spark plasma sintered CeO2 pellets with varying grain sizes (145 nm, 353 nm, and 101 μm) and a relative density greater than 93.83% were irradiated with 4 MeV Xe ions at a fluence of 2 × 1015 ions/cm2 at room temperature, followed by annealing at 600 °C for 3 h. Microstructure, including dislocation loops and bubble morphology of the irradiated samples, has been characterized. The average size of dislocation loops increases with increasing grain size. Large-sized dislocation loops are absent near the grain boundary because the boundary absorbs surrounding defects and prevents the dislocation loops from coalescing and expanding. The distribution of bubbles within the grain is uniform, whereas the large-sized and irregularly shaped xenon bubbles observed in the small grain exhibit pipe diffusion along the grain boundaries. The bubble diameter in the large-grained pellet is the smallest. As the grain size increases, the volumetric swelling of the irradiated pellets decreases while the areal density of Xe bubbles increases. Elemental segregation, which tends to occur at dislocation loops and grain boundaries, has been analyzed. Large-grained CeO2 pellet with lower-density grain boundaries exhibits better resistance to volumetric swelling and elemental segregation, suggesting that large-grained UO2 pellets could serve as a potential ATF.

Annealing Effect on Structural, Optical and Electrophysical Properties of ZnSe Nanocrystals Synthesized into SiO2/Si Ion Track Template.

We report the results of synthesis of zinc selenide (ZnSe) nanocrystals into SiO2/Si track templates formed by irradiation with 200 MeV Xe ions up to a fluence of 107 ions/cm2. Zinc selenide nanocrystals were obtained by chemical deposition from the alkaline aqueous solution. Scanning electron microscopy, X-ray diffractometry, Raman and photoluminescence spectroscopy, and electrical measurements were used for characterization of synthesized ZnSe/SiO2nanoporous/Si nanocomposites. XRD data for as-deposited precipitates revealed the formation of ZnSe nanocrystals with cubic crystal structure, spatial syngony F-43m (216). According to non-empirical calculations using GGA-PBE and HSE06 functionals, ZnSe crystal is a direct-zone crystal with a minimum bandgap width of 2.36 eV and anisotropic electronic distribution. It was found that a thermal treatment of synthesized nanocomposites at 800 °C results in an increase in ZnSe nanocrystallites size as well as an increase in emission intensity of created precipitates in a broad UV-VIS spectra range. However, vacuum conditions of annealing still do not completely prevent the oxidation of zinc selenide, and a formation of hexagonal ZnO phase is registered in the annealed samples. The current-voltage characteristics of the synthesized nanocomposites proved to have n-type conductivity, as well as increased conductivity after annealing.

Tuning critical current density properties of YBa2Cu3O y thin films under longitudinal magnetic field by using heavy-ion irradiation

We attempted to improve the critical current density J c under a longitudinal magnetic field (LMF) by using columnar defects (CDs) tilted toward the transport current, where the CDs were produced with 80 MeV Xe ions at an incident angle(s) up to φ i = 87.5° relative to the c-axis of YBa2Cu3O y thin films. The formation of CDs extending throughout the film was confirmed by cross-sectional transmission electron microscopy. The CDs tilted at φ i = 87.5° weakened the magnetic field dependence of J c under the LMF, providing a J c higher than that of the unirradiated film in a high magnetic field. This is the first study to demonstrate that CDs and/or irradiation defects contribute to flux pinning under the LMF in high-T c superconductors. In addition, the J c under LMF was sensitive to the tilt angle of the CDs: the J c was reduced by CDs tilted not only at φ i = 0°, but also at a slightly larger angle relative to the ab-plane, i.e. φ i = 85°. The introduction of CDs rather disturbs the LMF effect because of the large volume passing through the film thickness, unless the tilt angles of the CDs are within the narrow angular region effective for the LMF effect.

Luminescence Properties of ZrO2: Ti Ceramics Irradiated with Electrons and High-Energy Xe Ions.

Samples of ZrO2 ceramics with different concentrations of impurity titanium ions were synthesized by mixing zirconium and titanium oxide powders in different mass ratios. The X-ray diffraction analysis was used to determine the phase composition, lattice parameters, and crystallite size of the ceramics with varying dopant concentrations. Upon irradiation of the samples with 220 MeV Xe ions to a fluence of 1010 ions/cm2, a decrease in the intensity of the pulsed cathodoluminescence band at 2.5 eV was observed. Additionally, ion irradiation resulted in the emergence of a new thermoluminescence peak at 450-650 K attributed to radiation-induced traps of charge carriers. Further analysis revealed that the thermoluminescence curves of samples irradiated with electrons and ions comprise a superposition of several elementary peaks. Notably, a complex non-monotonic dependence of cathodo- and thermoluminescence intensity on titanium concentration was observed, suggesting the influence of concentration quenching and the presence of tunneling transitions.

Nanoscale core-shell structure and recrystallization of swift heavy ion tracks in SrTiO3.

It is widely accepted that the interaction of swift heavy ions with many complex oxides is predominantly governed by the electronic energy loss that gives rise to nanoscale amorphous ion tracks along the penetration direction. The question of how electronic excitation and electron-phonon coupling affect the atomic system through defect production, recrystallization, and strain effects has not yet been fully clarified. To advance the knowledge of the atomic structure of ion tracks, we irradiated single crystalline SrTiO3 with 629 MeV Xe ions and performed comprehensive electron microscopy investigations complemented by molecular dynamics simulations. This study shows discontinuous ion-track formation along the ion penetration path, comprising an amorphous core and a surrounding few monolayer thick shell of strained/defective crystalline SrTiO3. Using machine-learning-aided analysis of atomic-scale images, we demonstrate the presence of 4-8% strain in the disordered region interfacing with the amorphous core in the initially formed ion tracks. Under constant exposure of the electron beam during imaging, the amorphous part of the ion tracks readily recrystallizes radially inwards from the crystalline-amorphous interface under the constant electron-beam irradiation during the imaging. Cation strain in the amorphous region is observed to be significantly recovered, while the oxygen sublattice remains strained even under the electron irradiation due to the present oxygen vacancies. The molecular dynamics simulations support this observation and suggest that local transient heating and annealing facilitate recrystallization process of the amorphous phase and drive Sr and Ti sublattices to rearrange. In contrast, the annealing of O atoms is difficult, thus leaving a remnant of oxygen vacancies and strain even after recrystallization. This work provides insights for creating and transforming novel interfaces and nanostructures for future functional applications.

Neutrons and swift heavy ions irradiation induced damage in SiC single crystal

Radiation damage induced in SiC single crystal by neutrons and sequentially neutrons + 91.3 MeV Xe ions irradiations were characterised by optical measurements (absorption and photoluminescence) and Raman spectroscopy. The samples were first irradiated with neutrons then followed by irradiation with 91.3 MeV Xe ions. Our aim is to check electronic ionization-induced pre-existing defects annealing in SiC single crystal. The data obtained for samples irradiated by neutrons were compared to those of neutrons + ions. It is found that neutrons irradiation induced absorption band at 780 nm and two emission bands at 550 nm and 920 nm. Both bands 780 nm and 920 nm assigned to silicon vacancy (VSi). Compared to neutrons irradiation, the same absorption and emission bands are observed for neutron + ions irradiated samples, indicating similar types of defects formation by additional 91.3 MeV Xe ions. The bands growth rapid at low dose followed by a saturation effect above a dose of 2.0 × 10−4 dpa for neutrons and 10.6 × 10−3 dpa for neutrons + ions. The stress follows the same dose-dependence as the absorption band, suggesting a good correlation between the stress and the silicon vacancies (VSi). Raman results proved that additional 91.3 MeV Xe ions irradiation induced the pre-existing damage annealing in SiC crystal. However, at high pre-existing defects concentration and Xe ions dose a competition between defects creation and annealing takes place. To confirm the results experiments using Doppler Broadened Emission Spectroscopy (DBS) using Variable Energy Slow Positron Beam, are planned for our next study.

FORMATION OF DEFECTS IN THE ANION AND CATION SUBLATTICE OF MgAl<sub>2</sub>O<sub>4</sub> CRYSTALS IRRADIATED BY HIGH ENERGY XENON IONS

In this work, the optical characteristics of an aluminum-magnesium spinel irradiated with 220 MeV Xe ions, which simulate the effect of nuclear fuel fission fragments were studied. During the experiments, the transmission spectra were measured in the IR region (240–12500) cm−1, the optical absorption spectra in the range (2–7) eV, the Raman spectra were measured by the ion penetration depth, from the surface to 30 µm. In the optical absorption spectrum (2–8) eV of irradiated spinel crystals, a wide complex band of radiation-induced absorption is observed with a peak in the region of 5.3 eV associated with electronic color centers of the F + and F type, and hole color centers are responsible for optical absorption at ~ (3–4) eV. In the near IR region, the crystal retains its transparency. In the Raman spectrum, in addition to the Raman modes characteristic of an ideal crystal, additional modes, A1g* (720 cm−1), and Eg* (385 cm−1), appear mainly in the form of an asymmetric shoulder of the main Eg mode. As the depth increases, the A1g*/Eg ratio increases, reaching a maximum value of 0.05 at 6 µm, and remains practically unchanged until the end of the Xe ion range of 14 µm, and with a further decrease to 0.045 at a depth of 30 µm. That is, when irradiated with 220 MeV Xe ions, cation mixing occurs along the ion path.

Optical Characteristics of MgAl2O4 Single Crystals Irradiated by 220 MeV Xe Ions.

In In this study, the optical properties of magnesium-aluminate spinel were examined after being irradiated with 220 MeV Xe ions. The research aimed to simulate the impact of nuclear fuel fission fragments on the material. The following measurements were taken during the experiments: transmission spectra in the IR region (190-7000) nm, optical absorption spectra in the range (1.2-6.5) eV, and Raman spectra were measured along the depth of ion penetration from the surface to 30 µm. A peak with a broad shape at approximately 5.3 eV can be observed in the optical absorption spectrum of irradiated spinel crystals. This band is linked to the electronic color centers of F+ and F. Meanwhile, the band with a maximum at ~(3-4) eV is attributed to hole color centers. Apart from the typical Raman modes of an unirradiated crystal, additional modes, A1g* (720 cm-1), and Eg* (385 cm-1), manifested mainly as an asymmetric shoulder of the main Eg mode, are also observed. In addition, the Raman spectroscopy method showed that the greatest disordering of crystallinity occurs in the near-surface layer up to 4 μm thick. At the same time, Raman scattering spectroscopy is sensitive to structural changes almost up to the simulated value of the modified layer, which is an excellent express method for certifying the structural properties of crystals modified by swift heavy ions.

Photoluminescence of high energy xenon ion irradiated magnesium aluminate spinel single crystals

Laser confocal microscopy technique (60 ps laser pulse excitation at 445 nm) and a time-correlated single photon counting (TCSPC) technique have been used to study the photoluminescence (PL) in 152 MeV Xe ion irradiated MgAl2O4 single crystals. It was shown that radiation defects produced by swift xenon ions give rise to broad luminescence band positioned in the 470–800 nm wavelength range. The measurements of the PL decay curves have evidenced that lifetime of defect-related PL signal gradually increases from 6 to 10 ns in 500–620 nm spectral range and decreases with ion fluence increasing. The decrease of the luminescence intensity observed after fluences ∼1013 cm−2 is attributed to overlapping of individual ion track core regions.

RADIATION DEFECTS IN ZrO<sub>2</sub> NANOSTRUCTURAL COMPACTS IRRADIATED BY ELECTRON AND ION BEAMS

The thermoluminescence (TL) and EPR spectra of nanostructured compacts of monoclinic ZrO2 irradiated by three types of irradiation have been studied: impulse flow of 130 keV electrons, beam of 10 MeV electrons, as well as a 220 MeV Xe ion beam. Irradiation of samples with 10 MeV electrons and ions leads to the formation of F+ centers in them. Thermal destruction of these centers is observed in the temperature range 375–550 K for electron-irradiated compacts and 500– 700 K for ion-irradiated compacts. The drop in the concentration of F+ centers is associated with the depletion of traps responsible for TL peaks in the specified temperature range. In samples irradiated with an ion beam, new paramagnetic centers with g = 1.963 and 1.986 were found, in the formation of which, probably, Zr3+ ions and oxygen vacancies participate, thermal destruction occurs in the temperature range 500–873 K.

Defect evolution under intense electronic energy deposition in uranium dioxide

The coupled effects of nuclear and electronic energy losses were investigated in uranium dioxide (UO2). Single and sequential ion irradiations were carried out with 92 MeV Xe ions and 0.9 MeV I ions. Raman spectroscopy and X-ray diffraction analyses were combined with the inelastic thermal spike (iTS) model to investigate the effect of electronic ionizations on the ballistic damage. It appears that the high-energy ions induce a significant change in the defect distribution with an amplitude that depends on the level of pre-existing disorder. This modification essentially results in an acceleration of the transformation from the dislocation loops to the dislocation lines, a process that is accompanied by a stress relaxation. Surprisingly, with the fluence increase of 92 MeV Xe ions, the stress starts to increase again, highlighting a possible synergetic effect between the pre-existing defects and those generated by the 92 MeV Xe ions irradiation.

Mechanism of ion track formation in silicon by much lower energy deposition than the formation threshold

Mechanism of the ion track formation in crystalline silicon (c-Si) is discussed, particularly under 1–9 MeV C60 ion irradiation. In this energy region, the track formation was not expected because the energy E was much lower than the threshold of E th = 17 MeV determined by extrapolation from higher energy data in the past literature. The track formation is different between irradiations of C60 ions and of monoatomic ions: The tracks were observed under 3 MeV C60 ion irradiation but not under 200 MeV Xe ions, while both the irradiations have the same electronic stopping (S e) of 14 keV nm−1 but much higher nuclear stopping (S n) for the former ions. The involvement of S n is suggested for the C60 ions. While the inelastic thermal spike (i-TS) calculations predict that the high energy monoatomic ion irradiation forms the tracks, the tracks have never been experimentally detected, suggesting quick annihilation of the tracks by highly enhanced recrystallization in c-Si. Exceptions are C60 ions of 1–9 MeV, where the track radii are well reproduced by the i-TS theory with assuming the melting transition. Collisional damage induced by the high S n from C60 ions obstructs the recrystallization in c-Si. Then the tracks formed by the melting transition survive against the recrystallization. This is a new type of the synergy effect between S e and S n, different from the already-known mechanisms, i.e., the pre-damage effect and the unified thermal spike. While c-Si was believed as a radiation-hard material in the S e regime with high S e threshold, this study suggests that c-Si has a low S e threshold but with efficient recrystallization.

The effects of radiation-induced grain subdivision and dislocations on the fracture properties of uranium dioxide

Microcantilever bending tests were applied on uranium dioxide samples irradiated by 84 MeV Xe ions. Depending on the initial grain sizes, different levels of grain subdivision and dislocation development were observed near the irradiated surface. These radiation damage features were shown to degrade the fracture properties of both samples. The fundamental aspects of the radiation-microstructure-property relationships were discussed in this paper, taking a holistic consideration of the microcantilever bending data, fractography and microstructures. The separate effects of the irradiation-induced grain subdivision and dislocations on the fracture initiation and propagation of uranium dioxide were discussed. It was observed that radiation-induced dislocations and grain subdivision, without the presence of Xe bubbles co-located with the defects, cause reductions in the Young's modulus, fracture strain, and fracture stress, and a transition to intergranular fracture.

Correlation between radiation resistance and structural factors of ABO3-type perovskites

In this study, ABO3-type (A = Ca, Sr, Ba; B = Ti, Zr) perovskites were prepared by solid-state reaction method and then irradiated by 3 MeV Xe ion. Results show that the samples exhibit significant amorphization and lattice swelling under irradiation. The radiation resistance of ABO3 perovskites is strongly correlated to the structural factors which were proposed to describe the structural stability of perovskites. Specifically, radiation resistance of ABO3 perovskites deteriorates with increasing t and μ+tη and decreasing τ, where t is Goldschmidt’s tolerance factor, μ is the octahedral factor, η is the atomic packing fraction, and τ is a new tolerance factor. Furthermore, the decomposition energies of ABO3 perovskites were calculated to confirm the mentioned correlation. According to this study, it is suggested that structural factors may provide guidance for predicting the radiation resistance of perovskites and seeking for potential perovskites.

Influence of ion radiation on leaching behavior of borosilicate glass

Borosilicate glass is a promising material for immobilization of high-level radioactive waste (HLW). The leaching behavior of borosilicate glass is crucial for the safety of HLW deep geological disposal. Borosilicate glasses were irradiated with 5 MeV Xe ions. After irradiation, the leaching behaviors of borosilicate glasses were investigated using the MCC-1 static leaching method at 90 °C. The solutions were analyzed by inductively coupled plasma optical emission spectrometry. The structure of the glasses was characterized with Fourier transform infrared spectroscopy, Raman spectroscopy and grazing incident X-ray diffraction. With radiation of ions, [BO4] units were transformed into [BO3] units, which decreased the polymerization of glass network. The [BO3] units of glasses with and without irradiation both decreased gradually as the leaching time increased. After irradiation, the leaching rates of glasses increased obviously. The strength of the glass network deteriorated after irradiation and the structure of irradiated glass was more easily altered than pristine glass under leaching condition.

Formation of light-emitting defects in silicon by swift heavy ion irradiation and subsequent annealing

High-resistivity floating-zone silicon (FZ-Si) and n-type (4.5 Ohm·cm) Czochralski silicon (CZ-Si) wafers were irradiated at room temperature with 167 MeV Xe ions to fluences ranging from 5·1010 to 5·1011 cm−2. Temperature dependent photoluminescence (PL) measurements were performed to characterize the as-implanted and annealed silicon wafers. It was found that irradiation with swift heavy ions (SHI) leads to the formation of light-emitting defects in both types of silicon wafers. Low-temperature annealing (400 °C) leads to a significant increase of the photoluminescence intensity. In addition, the photoluminescence decreases for increasing measurement temperatures and eventually quenching is observed for temperatures larger than 80 K. The type of silicon wafer (FZ or CZ) does not significantly influence the defect-related light-emitting properties. This implies that low fluence SHI irradiation is a promising method for creation of light-emitting defects in silicon.

Swift heavy ion irradiation-induced amorphous iron and Fe–Si oxide phases in metallic57Fe layer vacuum deposited on surface of SiO2/Si

57Fe conversion electron Mössbauer (CEM) spectroscopy, SEM and magnetization measurements were used to study the effect of swift heavy ion irradiation on metallic 57Fe (10 nm) thin layer vacuum deposited onto SiO2/Si. About 85% of the total iron content of the surface layer detected by CEM was present as metallic, crystalline alpha iron before the irradiation, while upon irradiation with 160 MeV Xe ions, with a fluence of 5 × 1013 ion cm−2, ~ 21% was converted to amorphous iron and ~ 47% to silicon-containing iron oxide phases. The presence of pure iron in the amorphous state was evidenced by CEM in agreement with magnetization measurements. Temperature dependence of CEM measurements and the FC/ZFC curves of the irradiated deposit indicated superparamagnetic nature of the iron-silicon-oxide phases. The results are discussed in terms of the thermal spike model for the formation of the amorphous iron phase that can be essential for the formation of silicon-iron-oxides. Graphical abstract

Thermal conductivity of Al2O3 irradiated with swift heavy ions

• Comprehensive study of thermal conductivity under swift heavy ion irradiation. • Very strong effect of a narrow highly damaged track core on heat propagation. • Classical thermal transport model may be not valid for nanometric SHI tracks. Thermal transport in α -Al 2 O 3 irradiated with 167 MeV Xe ions is studied within direct method based on the Fourier law implemented into classical molecular dynamics. Formation of defective regions as a result of ion passages is described using the original multiscale approach developed in previous works. Degradation of the thermal conductivity coefficient of single-crystalline alumina with ion fluence shows reasonable agreement with the experimental thermoreflectance data. The applied method demonstrated good applicability in the considered case and allowed to distinguish effects of discontinuous crystalline tracks on thermal conductivity of the alumina target. It was surprisingly observed that a nanometric highly damaged core of swift heavy ion tracks strongly affect the heat transport in the irradiated material, which is in contradiction with classical Rayleigh model.

Morphology of Columnar Defects Dependent on Irradiation Direction in High-T c Superconductors

The morphologies of ion tracks tilted at different angles were systematically investigated by TEM observations on GdBCO coated conductors irradiated with 80 MeV Xe ions. The 80 MeV Xe ion beam along the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> -axis produced shortly segmented (discontinuous) columnar defects (CDs) along the ion path throughout the sample. When the ion beam was tilted at slight angle of 20° from the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> -axis, by contrast, not discontinuous CDs but thick and elongated (continuous) ones were formed in the irradiation direction. The formation of continuous CDs was observed to a deeper depth from the surface for the irradiation tilted at larger angle from the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> -axis. The variation of the microstructures against the irradiation angles was caused by the anisotropic temperature spread during the formation of CDs, which was attributed to the anisotropic thermal diffusivity in high- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> superconductors. We also demonstrated that discontinuous CDs could be formed at the irradiation angle of ±45° relative to the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> -axis into YBCO thin films by using 50 MeV Kr ions, which was the irradiation condition estimated backwards from the directional dependent morphology of CDs.

Ion-Track Template Synthesis and Characterization of ZnSeO3 Nanocrystals

ZnSeO3 nanocrystals with an orthorhombic structure were synthesized by electrochemical and chemical deposition into SiO2/Si ion-track template formed by 200 MeV Xe ion irradiation with the fluence of 107 ions/cm2. The lattice parameters determined by the X-ray diffraction and calculated by the CRYSTAL computer program package are very close to each other. It was found that ZnSeO3 has a direct band gap of 3.8 eV at the Γ-point. The photoluminescence excited by photons at 300 nm has a low intensity, arising mainly due to zinc and oxygen vacancies. Photoluminescence excited by photons with a wavelength of 300 nm has a very low intensity, presumably due to electronic transitions of zinc and oxygen vacancies.