Radiation Effects In Materials Research Articles

Radiation effects in materials

Radiation effects in materials

Irradiation damage reduces alloy corrosion rate via oxide space charge compensation effects

Radiation effects in materials often compound and accelerate other detrimental phenomena such as embrittlement, oxidation and creep. However, irradiation can also decrease the oxidation rate, for instance with ZrNb alloys nuclear fuel cladding. In this study, we rationalize this observation on Zr-0.5Nb alloy by introducing a mechanism based on oxide space charge modification, resulting from irradiation enhanced Nb clustering. This mechanism is investigated using a multiscale approach: from the macroscale, to determine post-irradiation oxidation kinetics, to the atomic scale, using in-situ atom probe tomography sample oxidation, to observe elemental solute redistribution across the oxide/metal interface. The mechanism is further supported by high resolution transmission electron microscopy characterization and density functional theory calculations. A point defect model is proposed to account for oxide space charge effects and their changes under irradiation. This integrated, multiscale experimental and modeling approach challenges the current paradigm on irradiation effects and how they can potentially improve materials performance in extreme environments.

Characterization of Mechanical Property Degradation of Ion-Irradiated Materials

Evaluating the degradation of mechanical properties under irradiation is crucial for nuclear structural materials. Although ion irradiations have been commonly used for fundamental research on irradiation effects and fast screening of potential materials, the mechanical property tests on ion-irradiated materials are challenging due to the shallow irradiation depth. The research progress on utilizing small-scale mechanical property tests to characterize the ion-irradiation induced mechanical property degradation is the focus of this review. While the current techniques can access the mechanical properties at the nano- to micro-scale from various perspectives, the rationality and accuracy of the existing data analysis models, e.g., for the size-dependence, remain unclear or debating, especially for the ion-irradiated materials, resulting in the lack of consistency and reliability of the evaluation of the irradiation effects of materials. Establishing a standardized method is highly demanded to quantitatively bridge the gap between micro- and macro-scale mechanical properties of ion irradiated materials.

Evolution of microstructures in radiation fields using a coupled binary-collision Monte Carlo phase field approach

The simulation of radiation effects in materials broadly falls into two categories. In the limit of short time and length scales lies the modeling of primary radiation damage, such as point defect creation, energy deposition, and ballistic mixing. This is followed by the modeling at longer time scales of thermally activated microstructure evolution and defect reactions, such as recombination, clustering, and coarsening. The binary collision Monte Carlo method is an established, numerically efficient method for the computation of primary radiation damage. Conversely, the phase-field method is a state-of-the-art technique for modeling microstructure evolution on longer time and length scales. We present a concurrent coupling of these two methods, overcoming the difference between the discrete object Monte Carlo paradigm for primary radiation damage and the continuum field variable approach for microstructure evolution. The coupling is bidirectional, in which the microstructure evolution in the MOOSE finite-element framework provides the spatial scattering data set for the charged particle transport and receives point defect, mass transport, and heat source terms from the simulated collision cascades that contribute to the field variable evolution. The concurrent coupling scheme is implemented in the code Magpie and demonstrated by investigating patterning for an irradiated immiscible binary model alloy. The results from the coupled binary collision Monte Carlo/phase-field simulations reproduce the results of analytical models for phase separation, and phase mixing and patterning, supporting the approach and indicating its utility for modeling real-world materials systems.

Positron annihilation spectroscopy study of radiation-induced defects in W and Fe irradiated with neutrons with different spectra

The paper presents new knowledge on primary defect formation in tungsten (W) and iron (Fe) irradiated by fission and high-energy neutrons at near-room temperature. Using a well-established method of positron-annihilation lifetime-spectroscopy (PALS), it was found that irradiation of W in the fission reactor and by high-energy neutrons from the p(35 MeV)-Be generator leads to the formation of small radiation-induced vacancy clusters with comparable mean size. In the case of Fe, smaller mean size of primary radiation-induced vacancy clusters was measured after irradiation with fission neutrons compared to irradiation with high-energy neutrons from the p(35 MeV)-Be generator. It was found that one of the reasons of the formation of the larger size of the defects with lower density in Fe is lower flux in the case of irradiation with high-energy neutrons from the p(35 MeV)-Be source. The second reason is enhanced defect agglomeration and recombination within the energetic displacement cascade at high energy primary knock-on-atoms (PKAs). This is consistent with the concept of the athermal recombination corrected (arc-dpa) model, although the measured dpa cross-section of both fission neutrons and wide-spectrum high-energy neutrons in W is between the conventional Norgett–Robinson–Torrens (NRT-dpa) and arc-dpa predictions. This means that the physics of the primary radiation effects in materials is still not fully known and requires further study through a combination of modeling and experimental efforts. The present data serve as a basis for the development of an improved concept of the displacement process.

Analysis of strain and disordering kinetics based on combined RBS-channeling and X-ray diffraction atomic-scale modelling

Ion beams delivered by particle accelerators are routinely used to emulate harsh, radiative environments and they also constitute the foundations of the modern microelectronics industry. To characterize irradiated materials, numerous experimental and computational techniques can be implemented, but it is extremely difficult to effectively intertwine them, and to compare the associated data. In the present work, we present an integrated, experimental and computational approach that uses a same set of molecular dynamics simulations to generate signals of Rutherford backscattering spectrometry in channelling condition and X-ray diffraction, with UO2 as a test-case material. From these signals, parameters to monitor the damage level are computed, compared and confronted with experimental data. Although the evolution of the strain and disordering kinetics obtained by simulations differ on an absolute scale from those obtained experimentally (a discrepancy inherent to the method used to generate the atomic-scale data), a very good relative agreement is obtained, which demonstrates the validity of the approach, hence providing a new tool for the fine study of irradiation effects in materials.

An Integrated Experimental and Computational Approach for the Investigation of Irradiation Effects in Materials

Ion beams delivered by particle accelerators are routinely used to emulate harsh, radiative environments and they also constitute the foundations of the modern microelectronics industry. To characterize irradiated materials, numerous experimental and computational techniques can be implemented, but it is extremely diffcult to effectively intertwine them, and to compare the associated data. In the present work, we present an integrated, experimental and computational approach that uses a same set of molecular dynamics simulations to generate signals of Rutherford backscattering spectrometry in channelling condition andX-ray diffraction, with UO2 as a test-case material. From these signals, parameters to monitor the damage level are computed, compared and confronted with experimental data. The good agreement that comes out demonstrates the validity of the approach, hence providing a new tool for the fine study of irradiation effects in materials.

Simulation of the energy spectra of swift light ion beams after traversing cylindrical targets: a consistent interpretation of experimental data relevant for hadron therapy

We have performed detailed simulations of the energy spectra, recorded at several angles, of proton and helium ion beams after traversing thin cylindrical targets of different nature (liquid water and ethanol jets, as well as a solid aluminium wire), in order to reproduce a series of measurements intended to assess the stopping power of 0.3–2 MeV ions. The authors of these experiments derived values of the stopping power of liquid water (a quantity essential for the evaluation of radiation effects in materials, particularly for radiotherapy purposes) that are ~10% lower than what is expected from other measurements and theories. In our simulations, instead of treating the stopping power as an unknown free parameter to be determined, we use as input the electronic stopping power accurately calculated within the dielectric formalism. We take into account in the simulations the different interactions that each projectile can experience when moving through the target, such as electronic stopping, nuclear scattering or electron charge-exchange processes. The detailed geometry of the target is also accounted for. We find that our simulated energy distributions are in excellent agreement with the published measurements when the diameter of the cylindrical targets is slightly reduced, what is compatible with the potential evaporation of the liquid jets. On the basis of such an excellent agreement, we validate the accuracy of the model we use to calculate electronic excitation cross sections for ions in condensed matter in its range of applicability (particularly the electronic stopping power) needed for charged particle transport models, and we offer a consistent, but alternative, interpretation for these experiments on ion irradiation of cylindrical targets.

Determination of the REE content, geological age, and absorbed alpha dose of allanite mineral from Palawan, Philippines

Allanite is a common accessory mineral in igneous rocks that contains significant amounts of rare‐earth elements (REEs), thorium (Th), and uranium (U). The presence of Th and U in the allanite exposes it to radiation resulting in radiation damage in its crystal structure and further leads to metamictization. Hence, allanite can be used as a natural analogue to assess the long‐term radiation effects in materials for high‐level nuclear waste disposal. It provides information on the effect of α‐decay on the crystal structure including the stability and integrity of the material. In this study, the absorbed α‐dose of allanite from Ombo, Palawan, Philippines, was estimated from the Th and U content and geological age of the mineral using X‐ray fluorescence and gamma‐ray spectrometry. The amount of Th and REE was measured to be around 1.37 and ~30.4 wt.%, respectively. Radiometric dating using gamma‐ray spectrometry estimated the age of the allanite mineral to be around 24–35 million years. Having obtained the amount of radioactivity and the time of exposure, the corresponding absorbed α‐dose was estimated to be at 2.84 × 1014 α‐decays/mg. Results suggest that the allanite mineral studied has not accumulated significant radiation damage to cause amorphization and still exhibit a crystalline structure. This study may provide data on the properties of allanite or silicate matrices as part of the ongoing studies on silicate minerals as natural analogues.

Object kinetic Monte Carlo methods applied to modeling radiation effects in materials

The object kinetic Monte Carlo (OKMC) method has proven to be an excellent tool to better understand microstructure evolution in irradiated materials, from metals to semiconductors. Its most valuable capability is that it provides a way to connect parameters obtained from fundamental models, such as first principles calculations, to experimental observations by expanding simulated time and length scales. However, the OKMC method has many limitations that pose questions on its predictive capabilities and an important effort is taking place to improve the model. In this review, first we describe the object kinetic Monte Carlo methodology, then a few examples are presented in the field of radiation damage of metals and the limitations of the method and its applicability discussed. To conclude, an outlook on the future of this computational model is given.

Modeling the impact of radiation-enhanced diffusion on implanted ion profiles

Ion irradiations are a valuable research tool for exploring radiation effects in materials. However, it is well recognized that the implanted ions can artificially modify the radiation damage evolution, e.g., enhancing amorphization processes at low irradiation temperatures and suppressing void swelling at elevated temperatures. Therefore, the implanted ion region should be avoided for most studies of ion irradiated materials. Due to increased interest in high damage, high temperature ion irradiations studying radiation effects in materials for proposed high dose Generation IV fission and fusion energy applications, it is crucial to quantify the extent of diffusional broadening of the implanted ion profile for a variety of temperatures, irradiation fluxes, and sink strengths. The present study summarizes computational analyses of thermal and depth-dependent radiation enhanced diffusion (RED) on diffusion broadening of the implanted ion profiles in Fe and Ni for a variety of irradiation conditions. For a low assumed RED coefficient (10−20-10−19 m2/s and 10−4 and 10−3 peak dpa/s, respectively) or high flux, broadening of the as-implanted ion profile is very small and a suitable artifact-free midrange region for analysis exists for ion energies above 5–6 MeV at 100 peak dpa. At high RED coefficients (10−19-10−18 m2/s and 10−4 and 10−3 peak dpa/s, respectively) broadening is much more significant, and no valid region for investigation exists below 6–8 MeV ion energies at any damage level >50 dpa. While increasing flux decreases irradiation time, it also increases the RED coefficient; these effects mostly offset except under recombination-dominant conditions. For typical high dose irradiation studies of void swelling that exceed ∼100 displacement per atom (dpa), ion energies >6–8 MeV must be employed in order to achieve suitable artifact-free midrange irradiation analysis regions, depending on the material system. Analysis of amorphization/precipitation require even higher energies (>10 MeV).

Mesoscale simulations of radiation damage effects in Materials: A SEAKMC perspective

Radiation damage presents a unique challenge for material simulations, with processes ranging from picoseconds to decades in time and nanometers to meters in length. Particularly, the understanding of many processes and fundamental mechanisms at the mesoscale are still lacking. In this paper, the self-evolving kinetic Monte Carlo (SEAKMC) method and its application to study mesoscale defect interaction is presented. SEAKMC is an off-lattice atomistic kinetic Monte Carlo approach which conducts ‘on-the-fly’ saddle point searches (SPS) using selective active volumes. The main components of SEAKMC are examined with focus on the comparative benefits of this method. Future areas of improvement are outlined, including suggestions for general improvements to SPS methods by reducing redundant searching and making predictive initial guesses for point defect migration events. Previous applications of SEAKMC to radiation effects in materials are briefly reviewed. Some potential applications of SEAKMC are given, including discussion of dislocation bias, and the further study of interaction between dislocation loops and point defects, which provide useful insights to understand void swelling, radiation induced segregation, and other important radiation damage processes.

Carbon Contamination During Ion Irradiation - Accurate Detection and Characterization of its Effect on Microstructure of Ferritic/Martensitic Steels

Accelerator-based ion beam irradiation techniques have been used to study radiation effects in materials for decades. Although carbon contamination induced by ion beams in target materials is a well-known issue in some material systems, it has not been fully characterized nor quantified for studies in ferritic/martensitic (F/M) steels that are candidate materials for applications such as core structural components in advanced nuclear reactors. It is an especially important issue for this class of material because of the strong effect of carbon level on precipitate formation. In this paper, the ability to quantify carbon contamination using three common techniques, namely time-of-flight secondary ion mass spectroscopy (ToF-SIMS), atom probe tomography (APT), and transmission electron microscopy (TEM) is compared. Their effectiveness and shortcomings in determining carbon contamination are presented and discussed. The corresponding microstructural changes related to carbon contamination in ion irradiated F/M steels are also presented and briefly discussed.

Opportunities and limitations for ion beams in radiation effects studies: Bridging critical gaps between charged particle and neutron irradiations

Ion beams are indispensible for understanding radiation effects in materials, enabling access to conditions challenging to perform with neutrons. However, ion irradiations can produce potential artifacts from beam rastering, high displacement damage rate effective “temperature shifts”, subthreshold collisions, high ionization rates, and non-monoenergetic primary knock-on atom energies. The influence of near-surface denuded zones and implanted ion effects is analyzed, including diffusional broadening effects. At high ion irradiation energies, “swift heavy ion” effects can lead to enhanced defect production or recovery. Ion energies of 10–50MeV typically offer a good compromise for minimizing near-surface, implanted ion, and swift heavy ion effects.

Dedicated Tool for Irradiation and Electrical Measurement of Large Surface Samples on the Beamline of a 2.5 Mev Pelletron Electron Accelerator: Application to Solar Cells

We designed a tool allowing irradiation of large samples over a surface of A5 size dimension by means of a 2.5 MeV Pelletron electron accelerator. in situ electrical measurements (I-V, conductivity, etc.) can also be performed, in the dark or under illumination, to study radiation effects in materials. Irradiations and electrical measurements are achievable over a temperature range from 100 K to 300 K.The setup was initially developed to test real-size triple junction solar cells at low temperature within the framework of the ESA’s JUICE mission. It will be made available to users at the beginning of 2017.After a brief description of the SIRIUS irradiation facility hosted at Laboratoire des Solides Irradies (LSI), this paper gives detailed information about the Large Surface Irradiated-Cell (LSIC) device. Preliminary results obtained during the ongoing qualification phase of the setup are also discussed.

<i>In-Situ</i> Observation of Radiation Damage Using a Combined Facility of Electron Microscope and Heavy-Ion Accelerator(s) —History and Future Prospectives—

Radiation effects in materials for fission and fusion reactors are caused by fast neutrons which produce cascade damage, which has been known to be considerably different from simple Frenkel pairs produced by relativistic electrons. In-situ observation of radiation damage using a combined facility of electron microscope and heavy-ion accelerators has been a powerful tool to investigate the nature of the cascade damage. In this overview, brief historical survey of this experimental technique will be given, followed by the results and discussions on cascade damage mainly in gold will be reviewed. Careful considerations will be required to generalize the results to other metals as well as to other experimental conditions. Finally, there are a number of points to be developed for better understanding of cascade damage and for extending the “in-situ” techniques to other materials as non-metallic solids and to other intriguing phenomena. [doi:10.2320/matertrans.MD201304]

Editor comments

This June 2013 Special Issue of the IEEE TRANSACTIONS ON NUCLEAR SCIENCE commemorates the 50th Anniversary of the IEEE International Nuclear and Space Radiation Effects Conference (NSREC). At the NSREC, held annually in July, scientists and engineers from industry, academia, and government institutions present their latest research on radiation effects in materials, electronic devices, circuits, and systems. The conference is the primary forum for technical presentations in the area of radiation effects, with attendance from over 20 countries around the world. It is also an important venue for companies to present their latest products and where students, young graduates, and experienced professionals meet, share ideas, and plan new experiments. Indeed, NSREC has been at the heart of the radiation effects community for 50 years. This special issue consists of review articles summarizing the research that has been published over the past ten years on subjects of interest to this community. The range of topics covered attests to our diversified and rich background.

Irradiation Effects in Materials for Nuclear Applications

Irradiation Effects in Materials for Nuclear Applications

Low-temperature Resistivity Measurements for Materials Development in Fusion Research

Comprehension of radiation effects in materials is still not totally well known. The combination of specific experiments and computational simulations is necessary to clarify the mechanisms of irradiation damage. Also it is one of the best strategies to carry out reliable bases for the development of correlations that will be able not only to provide trends that nuclear materials in operation are expected to follow, but also to guide the design of reactor components (DEMO) and properly guarantee their safety, maintenance and operational life. Main candidates as structural materials for future fusion reactors include: Austenitic Stainless Steels, Reduced Activation Ferritic/Martensitic (RAFM) steels: EUROFER, EUROFER ODS (9% Cr), ODS Ferritic Steels (12-14% Cr), W and W alloys, Cu alloys, V and V alloys.Low-temperature resistivity measurements represent one of the few techniques that allow “in-situ” and indirect evaluation of radiation effects in the atomic lattice of metallic materials as well as validation of multiscale modeling simulations. This work highlights the potential of such technique to study damage processes and reveals the interest of the fusion materials scientific community specifically for radiation effects modelling and experimental validation.

2012 Special NSREC Issue of the IEEE Transactions on Nuclear Science Comments by the Editors

The December 2012 special issue of the IEEE Transactions on Nuclear Science contains selected papers from the 49th annual IEEE International Nuclear and Space Radiation Effects Conference (NSREC) held July 16���20, 2012, in Miami, Florida USA. 95 papers presented at the 2012 NSREC were submitted for consideration for this year���s special issue. Those papers that appear in this special issue were able to successfully complete the review process before the deadline for the December issue. A few additional papers may appear in subsequent issues of the TRANSACTIONS. This publication is the premier archival journal for research on space and nuclear radiation effects in materials, devices, circuits, and systems. This distinction is the direct result of the conscientious efforts of both the authors, who present and document their work, and the reviewers, who selflessly volunteer their time and talent to help review the manuscripts. Each paper in this journal has been reviewed by experts selected by the editors for their expertise and knowledge of the particular subject areas. The peer review process for a typical technical journal generally takes six months to one year to complete. To publish this special issue of the IEEE Transactions on Nuclear Science (in December), the review process, from initial submission to final form, must be completed in about 10 weeks. Because of the short schedule, both the authors and reviewers are required to respond very quickly. The reviewers listed on the following pages contributed vitally to this quick-turn review process.We would like to express our sincere appreciation to each of them for accepting this difficult, but critical role in the process. To provide consistent reviews of papers throughout the year, the IEEE Transactions on Nuclear Science relies on a year-round editorial board that manages reviews for submissions throughout the year to the TRANSACTIONS in the area of radiation effects. The review process is managed by a Senior Editor and six Associate Editors who are technically knowledgeable in one or more specializations and are experienced in the publication process. This editorial process works very well. With twice the number of editors as previously used for overseeing the review process, each editor is able to devote more time to individual papers.