Kr Irradiation Research Articles

The synergetic effect of He and Kr irradiation on helium bubble evolution in SiC/SiC composite: Combining in-situ TEM observation with MD simulation

SiC fiber reinforced SiC matrix composites (SiC/SiC composites) are considered as one of the promising structural materials for liquid type breeding blanket in the fusion energy system. The transmutation gas production rate in fusion reactor is significantly higher compared with fission reactors. An innovative method combining in-situ irradiation and TEM observation and MD simulation was utilized to evaluate the synergetic effects of helium and irradiation on SiC/SiC composites. A comprehensive experiment matrix including Kr irradiation, He pre-implantation with sequential Kr irradiation as well as simultaneous dual beam at 1073 K to 16 dpa and 2400 appm He (150 appm/dpa) was performed using 800 keV Kr and 50 keV He ions. With the support of MD results, the impact of relative concentration ratio of vacancies and helium atoms on the bubble evolution was systematically investigated and the corresponding mechanism was further unraveled, which provides the basis of limiting the bubble density in SiC/SiC composites. Additionally, the direct evidence for the competition of irradiation-assisted bubble growth and re-dissolution was in-situ observed in SiC matrix for the first time.

Fully discrete model of kinetic ion-induced electron emission from metal surfaces

Ion-induced electron emission (IIEE) is an important process whereby ions impinging on a material surface lead to net emission of electrons into the vacuum. While relevant for multiple applications, IIEE is a critical process of electric thruster (ET) operation and testing for space propulsion, and, as such, it must be carefully quantified for safe and reliable ET performance. IIEE is a complex physical phenomenon, which involves a number of ion-material and ion-electron processes, and is a complex function of ion mass, energy, and angle, as well as host material properties, such as mass and electronic structure. In this paper, we develop a discrete model of kinetic IIEE to gain a more accurate picture of the electric thruster chamber and facility material degradation processes. The model is based on three main developments: (i) the use of modern electronic and nuclear stopping databases, (ii) the use of the stopping and range of ions in matter to track all ion and recoil trajectories inside the target material, and (iii) the use of a scattering Monte Carlo approach to track the trajectories of all mobilized electrons from the point of first energy transfer until full thermalization or escape. This represents a substantial advantage in terms of physical accuracy over existing semi-analytical models commonly used to calculate kinetic IIEE. We apply the model to Ar, Kr, and Xe irradiation of W and Fe surfaces and calculate excitation spectra as a function of ion depth, energy, and angle of incidence. We also obtain minimum threshold ion energies for net nonzero yield for each ion species in both Fe and W and calculate full IIEE yields as a function of ion energy and incidence angle. Our results can be used to assess the effect of kinetic electron emission in models of full ET facility testing and operation.

Irradiation stability and damage mechanism of Ln(1-x)SrxZrO(3.5–0.5x) (Ln[dbnd]La, Nd, Sm, Eu, Gd) ceramic waste form under Kr irradiation

As a quick and affordable experimental technique, the heavy ion irradiation method may quickly learn about the correlation between the degree of amorphization and structural modification of samples with varying ion implantation. Using the heavy ion irradiation technique, the irradiation stability of multiphase ceramic waste made of Ln2Zr2O7/SrZrO3 was assessed. Here, we found that multiphase ceramic waste forms still exhibit excellent radiation resistance while achieving high capacity and weak selectivity for immobilization of actinide nuclides (simulated by lanthanide elements) and fission products 90Sr (replaced by 89Sr). The analysis of grazing incidence and Raman spectroscopy provides evidence for explaining the radiation damage mechanism caused by 84Kr15+ heavy ions. Analysis of grazing incidence offers proof of the manner and extent of radiation damage brought on by 84Kr15+ ions. The impact and mechanism of crystal structure on radiation resistance in multiphase ceramics are discussed.

Effect of substrate thinning on heavy ion induced single event effect in silicon carbide power junction barrier Schottky diodes

Experimental responses of two different substrate thicknesses of SiC Junction-Barrier-Schottky (JBS) diodes are presented by Kr and Bi ions irradiation experiments. Three bias voltages of 250 V, 275 V, and 300 V were chosen to analyse single event leakage current (SELC) degradation and single event burnout (SEB) in the 650 V-rated devices with standard (350 μm) and thin (150 μm) substrates, respectively. Measured data indicate that under the same bias voltage and heavy ion parameter conditions, the degree of leakage degradation of the device is weaker for the SiC JBS with thin substrate structure. Measured data also indicate that when the device at a bias voltage of 300 V by the Bi-ion irradiation experiment, SEB occurred in the standard substrate device, but only leakage current degradation occurred in the thin substrate device. The weakening of effective charge deposition and impact ionization rate in thin-substrate devices are the main reasons for SELC degradation and SEB threshold increasing. Corresponding TCAD simulations are also utilized to analyse physical parameters and confirm the mechanism.

Theoretical Study of Intermixing in Au/Si System under Swift Heavy Ion Irradiation

Abstract: The behavior of the metallic multilayer Au100Å/Si100Å/Si under swift heavy ion irradiation has been studied within the inelastic thermal spike model. Gold has been chosen due to its insensitivity to irradiation. The heat transport in the electronic and lattice subsystem has been simulated using a three-dimensional numerical code that includes the energy transfer between the layers in a direction perpendicular to layer surfaces. The simulations have been done for four kinds of ions Pb, Xe, Kr, and Ar, at a specific energy of 3Mev/amu in order to study the influence of the electronic stopping power on the intermixing process. The results show that for Pb, Xe, and Kr, intermixing at the interface of Au/Si has been obtained. However, no mixing has been observed with Ar. Furthermore, the value of the interdiffusion coefficient for Au has been estimated to be approximately 11x10-4 cm2 s-1, which is characteristic of the liquid phase and, thus, supports the thermal spike model of mixing. For comparison, similar thermal spike simulations have been applied to Ti100Å/Si100Å/Si under the same irradiation conditions. We have found that Ti, which is a sensitive material, exhibits considerable intermixing with Si during Pb, Xe, and Kr irradiation. Whereas, a weak intermixing has been found after Ar irradiation; this is completely different from what has been observed in the Au/Si system. Keywords: Irradiation, Swift heavy ions, Thermal spike model, Ion beam mixing. PACS: 61.80.Az, 61.80.Jh, 61.80.LJ.

Helium in Cu-Ag-Fe triphase immiscible nanocomposites: An in situ sequential dual beam TEM study

Helium (He) generated during irradiation is notorious for inducing volumetric swelling and grain boundary embrittlement. It is imperative to design advanced materials with effective capability to manage He. Here, we report a largelydifferent bubble swelling behavior in Cu50Ag50, Cu45Ag45Fe10 and Cu33Ag33Fe34 nanocomposites with similar grain sizes. In situ He pre-injection leads to similar He bubble size and density in all three alloy systems. After subsequent Kr irradiation, the average bubble size and swelling in Cu33Ag33Fe34 is much less than Cu50Ag50. Additionally, while bubble size is much greater along triple junctions and grain boundaries than in matrix in Cu50Ag50, the bubble size at the triple junctions in Cu33Ag33Fe34 is much less, suggesting the vital role of Cu-Ag-Fe triphase triple junctions and phase boundaries in managing He. The present study provides new perspective for improving the radiation tolerance of nanocrystalline alloys by microstructure design.

In-situ radiation response of additively manufactured modified Inconel 718 alloys

In this study, a novel alloy of modified Inconel 718 produced by laser powder bed fusion is studied before and after in-situ Kr irradiation up to 3 dpa at 200 and 450 °C. Before irradiation, the microstructure consists of dislocation cells having a misorientation angle less than 5° and with an average size of ~500 nm. There are also second phase particles of MC type carbides, Laves phase and oxides such as Y-O, Y-(Ti)-Al-O. While the microstructure consists of stacking fault tetrahedra, faulted and perfect loops after irradiation at 200 °C, dislocation loops are the primary defects at 450 °C. With increasing dose, the size of the defects remains similar at 200 °C while it increases at 450 °C. This has been attributed to the existence of vacancy type defects at 200 °C and the different defect transport mechanisms at different temperatures. Moreover, matrix and second phase particle compositions seem to be similar after irradiation. The sink strengths of the structures have been calculated and superior radiation resistance of this alloy has been attributed to the existence of fine cell boundaries stabilized by the second phase particles produced by additive manufacturing.

Irradiation-induced large bubble formation and grain growth in super nano-grained ceramic

In this work, 0.5TRPO•0.5Gd2Zr2O7 ceramic with an average grain size of only ∼15 nm was prepared by a high pressure (5 GPa/520 °C) sintering method. Phase evolutions and microstructure changes of the as-fabricated super nano and micron-grained ceramics under a high-dose displacement damage induced by 300 keV Kr2+ ions were investigated. The results show that the super nano-grained ceramic has low degree of amorphization, obvious grain growth (2–3 times in grain size) and big Kr bubbles (10–68 nm) formation after irradiation. The micron-grained ceramic was severely amorphized after irradiation and many microcracks were formed parallel to its surface. The formation mechanism of Kr bubbles in the super nano-grained ceramic is on account of grain boundary diffusion and migration induced by the accumulation of the injecting Kr ions and irradiation defects. Nevertheless, microcracks formed in the micron-grained sample are caused by the accumulation of Kr atoms.

Intrinsic Vulnerability to Soft Errors and a Mitigation Technique by Layout Optimization on DICE Flip Flops in a 65-nm Bulk Process

We found that specific pairs of pMOS and nMOS transistors in dual interlocked storage cell flip flop (DICEFF) become sensitive to soft errors by device simulations. We propose several layout structures that can improve soft-error tolerance with additional 39%-46% area overhead. We evaluated soft-error tolerance of a D-type FF (DFF) and DICEFFs in a 65-nm bulk process by heavy ions. Our experimental results showed that the DICEFF has more than 300× better soft-error tolerance than the DFF by Kr (LET 40.3 MeV·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /mg) irradiation when the supply voltage is 1.2 V, and the DICEFF has only 9× better soft-error tolerance than the DFF when the supply voltage is 0.6 V. However, the proposed DICEFF with 46% area overhead has 58× better soft-error tolerance than the DFF when the supply voltage is 0.6 V. DICEFF has so many sensitive pairs and lower soft-error tolerance as supply voltage decreases that cannot be applied to highly scaled process technologies.

On the microstructure evolution of a nuclear-use steel after heavy ion irradiation

A nuclear-use ferritic-martensitic steel was irradiated by 196 MeV Kr ions. Both the low damage level area and the high damage level area were investigated by a transmission electron microscope (TEM), to reveal the irradiated microstructural features. In low damage level area ranging from surface to 6 μm depth, there were a few dislocation loops and black dots induced by Kr irradiation. The type of dislocation loops could be primarily ao<100> or ao/2<100> type. In addition, it was found that the sink effect of grain boundaries and stability of small precipitates were evident.

Impact of krypton irradiation on a single crystal tungsten: Multi-modal X-ray imaging study

Understanding microstructural and strain evolutions induced by noble gas production in the nuclear fuel matrix or plasma-facing materials is crucial for designing next generation nuclear reactors, as they are responsible for volumetric swelling and catastrophic failure. We describe a multimodal approach combining synchrotron-based nanoscale X-ray imaging techniques with atomic-scale electron microscopy techniques for mapping chemical composition, morphology and lattice distortion in a single crystal W induced by Kr irradiation. We report that Kr-irradiated single crystal W undergoes surface deformation, forming Kr containing cavities. Furthermore, positive strain fields are observed in Kr-irradiated regions, which lead to compression of underlying W matrix.

Revealing the synergistic effects of sequential and simultaneous dual beam irradiations in tungsten via in-situ TEM

Elucidating the synergistic effects of different energetic beams on the radiation response of nuclear materials is critical for developing an improved methodology for their evaluation when exposed to extreme environments. This article describes in-situ sequential (He implantation followed by Kr irradiation and vice-versa) and simultaneous (heavy ion Kr irradiation and He implantation) dual beam irradiations performed on tungsten at 1223 K. Dislocation loop density, average area, and total loop damage as a function of irradiation history and dose/fluence are quantified. The loop Burgers vectors and cavity damage (cavity density, size and total change in volume) are also determined at the final maximum dose for each condition. The loop damage evolution was different in all cases, with the smallest loop damage observed in the simultaneous experiment. Annihilation of Kr generated dislocation loops during He implantation in the Kr + He experiment was an unanticipated observation that may be explained by the dynamic evolution of dislocation loop sink strengths and time-dependent defect fluxes. Dislocation loop raft formation, denuded zones near extended defects, and cavity damage are compared across the different conditions. The phenomena observed and discussed in this work will stimulate further experimental and computational modeling activities leading to improved fundamental understanding of the irradiation response of nuclear materials under reactor-similar environments.

Enhancement of hydroxyapatite dissolution through structure modification by Krypton ion irradiation

Hydroxyapatite (HA) synthesized by a wet chemical route was subjected to heavy ion irradiation, using 4 MeV Krypton ion (Kr17+) with ion fluence ranging from 1 × 1013 to 1 × 1015 ions/cm2. Glancing incidence X-ray diffraction (GIXRD) results confirmed the phase purity of irradiated HA with a moderate contraction in lattice parameters, and further indicated the irradiation-induced structural disorder, evidenced by broadening of the diffraction peaks. High-resolution transmission electron microscopy (HRTEM) observations indicated that the applied Kr irradiation induced significant damage in the hydroxyapatite lattice. Specifically, cavities were observed with their diameter and density varying with the irradiation fluences, while a radiation-induced crystalline-to-amorphous transition with increasing ion dose was identified. Raman and X-ray photoelectron spectroscopy (XPS) analysis further indicated the presence of irradiation-induced defects. Ion release from pristine and irradiated materials following immersion in Tris (pH 7.4, 37 ℃) buffer showed that dissolution in vitro was enhanced by irradiation, reaching a peak at 0.1dpa. We examined the effects of irradiation on the early stages of the mouse osteoblast-like cells (MC3T3-E) response. A cell counting kit-8 assay (CCK-8 test) was carried out to investigate the cytotoxicity of samples, and viable cells can be observed on the irradiated materials.

Nanocrystalline ZrN thin film development via atomic layer deposition for U-Mo powder

Zirconium nitride (ZrN) thin film deposited via thermal atomic layer deposition (ALD) has been recently chosen as a candidate technology for application of a diffusion barrier coating on the low enriched uranium alloy powder considered in the NNSA research reactor conversion program. Reported here is the first instance of using ALD for coating actinide materials. For this study, a modified ALD system was constructed to produce one micron thick zirconium nitride (ZrN) coating over spherical particulate of natural uranium-molybdenum (U-Mo) based fuel. The ALD system was designed to have a rotating drum system, with provisions for facilitating sequential exposures of chemicals such as tetrakis dimethyl amido zirconium (TDMAZr) and ammonia (NH3) in order to deposit ZrN. The ALD system was successful in developing a highly conformal ZrN coating covering every individual U-7Mo particle. This article describes the ZrN film synthesis details and reports the produced microstructure and composition of the ALD ZrN as deposited on fuel particulates. The as-fabricated coating was determined to have a nanocrystalline structure in the cubic-ZrN (cF8) phase. It exhibited a dense microstructure with adequate interfacial bonding. TEM-EELS characterization demonstrated that the coating contains a very low amount of oxygen impurity. To understand the potential microstructural evolution for ALD ZrN during reactor operation, an in-situ heavy ion (Kr) irradiation experiment was performed at the IVEM-Tandem facility. A total fluence of 7.5 × 1015 ions/cm2 (∼10 dpa) was achieved, and apart from minor grain coarsening in the ALD ZrN coating, no significant radiation effects were observed.

Light He and heavy Kr ions irradiation effects in orthorhombic Tb2TiO5 ceramics

Polycrystalline Tb2TiO5 pellets with orthorhombic structure were irradiated with 400 keV He+ and 800 keV Kr2+ ions at room temperature. Ion-irradiation-induced microstructural evolution is characterized using grazing incidence X-ray diffraction and cross-section transmission electron microscopy. A crystalline to amorphous transformation was observed in orthorhombic Tb2TiO5 as the samples were irradiated with heavy Kr2+ ions. However, the orthorhombic Tb2TiO5 was observed to transform into a cubic fluorite structure for light He+ irradiation. Furthermore, this phase transformation is accompanied by a decrease in unit cell volume of approximately 4.53%. No amorphization was observed even to the highest fluence of 2 × 1017 He/cm2. The observations are discussed on the basis of dense cascade and defects accumulation from heavy and light ion irradiation, respectively. Moreover, the electronic to nuclear stopping power is introduced to help better understand the He and Kr irradiation results.

High thermal coarsening resistance of irradiation-induced nanoprecipitates in Cu-Mo-Si alloys

Irradiation by 1.8 MeV Kr ions at room temperature (RT) was employed to induce nanoprecipitation in two Cu-Mo-Si ternary alloys, Cu96Mo1Si3 and Cu90Mo3.5Si6.5. The nature and the stability of these precipitates during high temperature annealing and irradiation were studied using X-ray diffraction and transmission electron microscopy. In Cu90Mo3.5Si6.5, Kr irradiation at RT resulted in the formation of a high number density (>1023 m−3) of Mo-Si rich nanoprecipitates, ∼3 nm in size, the formation of which was attributed to Mo-Si interactions during the thermal spike phase of displacement cascades. The size of these irradiation-induced Mo-Si precipitates remained unchanged after annealing at 750 °C for 1hr. This near absence of thermal coarsening contrasted with a significant thermal coarsening of the more Mo-rich precipitates formed by direct annealing in that same ternary alloy, and with the even larger coarsening of pure Mo precipitates formed by RT irradiation in binary Cu-Mo alloys. During high temperature irradiation, precipitation is also observed, and some precipitates were significantly enriched in Mo. As for thermal annealing, those precipitates displayed increased coarsening. The remarkable thermal coarsening resistance of RT irradiation-induced Mo-Si precipitates is attributed to the suppression of Mo solubility in a Cu matrix containing Si-rich precipitates, and to the narrow precipitates size distribution generated by RT irradiation. This former point was quantified using thermodynamic calculations with the CALPHAD method.

Antioxidant properties variation in radiation induced genotypes of jatropha

Jatropha curcas L. produces seed oil believed to have immense potential as an economical alternative for diesel fuel. This study was undertaken to evaluate effect of gamma rays with rate of 10, 20 and 30 kR on biochemical characteristics of leaves among seven genotypes. Result showed that Chhatrapati genotype performed better for various biochemical properties such as total soluble sugar, protein, free amino acid, total phenol content and moisture content than other genotypes. However, guaiacol peroxidase activity was found to be higher in Hansot genotype. Maximum superoxide dismutase activity was recorded in SKN Big genotype. The increase in gamma rays irradiation progressively increases total soluble sugar, protein, free amino acid, total phenol content, superoxide dismutase (SOD) and guaiacol peroxidase (GPOX). The interaction effect of genotypes and gamma rays treatment were found to be significant for GPOX activity. The significantly highest GPOX activity was recorded under Chhatrapati genotype at 30 kR irradiation. However, the interaction effect of genotype and gamma rays treatment of other biochemical traits like total soluble sugar, protein, free amino acid, total phenol content and moisture content were nonsignificant during field growth stage.

Nanomechanical testing of ODS steels irradiated with 1 MeV/amu heavy ions

Development of oxide dispersion strengthened (ODS) steels, as candidates for fuel claddings for Gen IV nuclear reactors, requires a comprehensive study of their behaviour under operating conditions. In this work, 1.2 MeV/amu Kr and Xe irradiation was used to simulate fission fragment impact. New irradiation approaches with respect to a non-homogeneous damage profile under ion irradiation were proposed. Hardness profiles of irradiated ODS steels were obtained by continuous stiffness measurements with subsequent analysis of size effects according to the Nix–Gao model. It was found, that heavy ion irradiation leads to hardness saturation in ODS steels in a damage dose range of 0.1–1 dpa. Observed hardening is about 20% and is not connected with the radiation stability of Y–Ti–O and Y–Al–O oxide particles in ODS steels as it was studied by TEM.

Structural damage in InGaN induced by MeV heavy ion irradiation

In0.18Ga0.82N films were irradiated with 4MeV 84Kr and 8.9MeV 209Bi ions to various fluences at room temperature. The irradiated films were analyzed by means of Rutherford backscattering/channeling (RBS/C) and high resolution X-ray diffraction (HRXRD). The RBS/C measurements show that under the irradiation conditions, the relative lattice disorder in the films, obtained from the normalized backscattering yield, exhibits a rapid increase in the range from ∼2% to 68%. There is also an increasing lattice expansion of the films with increasing ion fluence, as determined by the HRXRD measurements. At a comparable level of lattice disorder, the Kr irradiation leads to a more pronounced lattice expansion than the Bi irradiation. This may be attributed to a larger portion of the single interstitials in the films produced by the lighter Kr ion irradiation.

Strong irradiation tolerance to amorphization in delta-Sc4Ti3O12

Polycrystalline delta-phase Sc4Ti3O12 was irradiated under two separate conditions, with 200keV Ne+ or 600keV Kr3+ at cryogenic temperature (∼77K) to examine its radiation tolerance to amorphization. Irradiated samples were characterized using grazing incidence X-ray diffraction and cross-sectional transmission electron microscopy. An order-to-disorder (O–D) structural transformation was observed under both ion beam irradiation conditions, but the threshold irradiation doses to produce the O–D transformation differ significantly. The order to disorder phase transformation was completed by a fluence of 2×1019Ne/m2 (or a peak dose of ∼0.7dpa) with Ne irradiation, while it was not accomplished until a fluence of 5×1020Kr/m2 (or a peak dose of ∼93dpa) with Kr irradiation. This observation was interpreted in terms of greater probability of defect survivability in dilute Ne versus dense Kr ion cascades. More interesting aspect in this study, in the basis of so-called “chemical effects”, Ti-bearing oxide Sc4Ti3O12 should be readily amorphous when exposed to ion irradiation, but no amorphization was observed even after 93 displacements per atom in Kr irradiation. These observations exhibit that the temperature–composition (T–C) phase diagram is a good indicator for radiation tolerance, especially for amorphization.