Radiation Damage Production Research Articles

Radiation stability of fluorite-type nuclear oxides

Oxides with the fluorite-type structure are radiation tolerant materials. They are widely used or envisaged in hostile nuclear environments, such as nuclear fuels or inert transmutation matrices for actinide burning. Study of the radiation stability of this class of solids in various radiative fields is of major importance. Two issues which may affect the stability of materials are considered in this work: the production of radiation damage (ballistic contribution); the modification of the matrix composition by doping (chemical contribution). Both contributions may drastically affect the solid stability. Urania and zirconia single crystals were chosen as fluorite-type canonical systems. They were implanted with low-energy inert gases (He or Xe). The damage in-growth, due to both ballistic and chemical contributions, was investigated by in situ RBS/C experiments in the channelling mode and TEM. Two main steps in the disordering kinetics were observed for both inert gases. Relevant key parameters were found to be: the number of displaced lattice atoms created by the slowing-down of energetic ions during the implantation process; the concentration of noble gas atoms in the solid which cause the formation of large stress fields surrounding gas aggregates.

Radiation stability of ceramics: Test cases of zirconia and spinel

The study of the effects of radiation in ceramics of potential use in electronic, space and nuclear industries appears to be a major challenge in the next decades. The collect and analysis of data dealing with the production and recovery of radiation damage in this type of materials are thus tasks of prime interest. In this article, we present a review of the main structural and chemical modifications observed in test case ceramics (yttria-stabilized zirconia and magnesium-aluminate spinel) submitted to ion bombardment and thermal treatments. We show that the stability under irradiation depends on the intrinsic properties of the materials and on irradiation parameters such as the ion energy, fluence and temperature. We also demonstrate that the recovery of damage upon annealing at elevated temperatures induces drastic physico-chemical modifications of the matrix.

Physicochemical modifications induced by ion bombardment and thermal treatments in zirconia and spinel

The evaluation of the damage generated in ceramic oxides exposed to radiations is a major challenge in many technological domains which cover electronic, space and nuclear industries. Thus there is a great need of data concerning the production and recovery of radiation damage in this type of materials. This work aims to present a short review of the main structural and chemical modifications recently observed in yttria-stabilized zirconia and magnesium aluminate spinel that are submitted to ion bombardment and thermal treatments.

Multiscale Modelling of bcc-Fe Based Alloys for Nuclear Applications [PowerPoint Submission

AbstractUnderstanding the basic mechanisms that determine microstructure changes in neutron irradiated steels is vital for a safe lifetime management of existing nuclear reactors and a safe design of future nuclear options. Low-alloyed ferritic steels containing Cu, Ni, Mn and Si as principal solute atoms are used as structural materials for current reactor vessels. The microstructural evolution under irradiation in alloys is decided by the interplay between defect formation and thermodynamic driving forces, together determining the appearance of phase transformations (precipitation, segregation, …) and favouring or delaying the nucleation and growth of point-defect clusters, their diffusion and their mutual recombination or removal at sinks. A reliable description of the production, evolution and accumulation of radiation damage must therefore start from the atomic level and requires being able to describe multicomponent systems for timescales ranging from few picoseconds to years. This goal demands firstly the fabrication of interatomic potentials for alloys that must be both consistent with the thermodynamic properties of the system and capable of reproducing correctly the characteristic solute-point defect interactions, versus ab initio or experimental data. Secondly the performance of extensive molecular dynamics (MD) simulations, to grasp the main mechanisms of defect production, diffusion, mutual interaction, and interaction with solute atoms and impurities. Thirdly, the development of simulation tools capable of describing the microstructure evolution beyond the timeframe and lengthscale of MD, while reproducing as much as possible the atomic-level origin of the mechanisms governing the evolution of the system, including phase changes.In this presentation the results of recent efforts made in this direction in the case of Fe-Cu, Fe-Cr and Fe-Ni alloys, as basic model alloys for the description of steels of technological relevance, are highlighted. In particular, advanced techniques to fit interatomic potentials consistent with thermodynamics are proposed and the results of their application to the mentioned alloys are presented. Next, the development of advanced methods, based on the use of artificial intelligence, to improve both the physical reliability and the computational efficiency of kinetic Monte Carlo codes for the study of point-defect clustering and phase changes beyond the scale of MD, is reported. These recent progresses bear the promise of being able, in the near future, of producing reliable tools for the description of the microstructure evolution of realistic model alloys under irradiation.

The effects of interfaces on radiation damage production in layered metal composites

Molecular dynamics computer simulations of 5 keV displacement cascades near cube-on-cube Cu–Ni interfaces have been performed. Both coherent interfaces (with large coherency stresses) and semi-coherent interfaces (with misfit dislocations in the interface) typical of nanolayer metal composites are considered. The primary damage state of cascades from 5 keV recoil atoms in the composite differs from that in cascades generated in pure Cu and Ni. In the semi-coherent case some defect clusters form directly on the misfit dislocations. Excluding these, the defect yields for both interface types are about two-thirds of the average yield of defects for cascades in the pure metals. In single cascades, as well as for overlapping multiple cascades, the numbers of surviving defects in the semi-coherent interface are significantly different in the Cu and Ni layers, but they are the same in Cu and Ni for the coherent case. Anti-site atomic mixing occurs near both types of interfaces, more so in the coherent case.

Radiation damage on 6H-SiC Schottky diodes

The radiation damage production rate in SiC Schottky diodes was studied by measuring the ion beam induced charge (IBIC) from a 2 MeV He + ion microbeam. Two 30 μm diameter SiC Schottky diodes with a Ni Schottky contact were fabricated on 5 μm thick epilayers of both n-type and p-type 6H-SiC. An area of 10 μm × 10 μm on each Schottky diode was irradiated by a scanned 2 MeV He + ion beam focused to less than 1 μm in diameter with a dose range from 1 × 10 9 to 1 × 10 13 ions/cm 2. Before and after He + ion beam irradiation, IBIC spectra were measured at the irradiated area. From these spectra, the relationship between the IBIC peak shift and the He + ion beam dose was measured. For the n-type and p-type diodes, the IBIC pulse height was found to decrease from the initial height by 27% at 7.6 × 10 11 ions/cm 2 irradiation and 29% at 1.1 × 10 11 ions/cm 2, respectively.

Atomic-scale modelling of primary damage and properties of radiation defects in metals

Considerable success has been achieved in recent years in the understanding of radiation damage production in high-energy displacement cascades, the properties of the defects and evolution of radiation damage in metals. Two main reasons form the basis of this success. First, the significant increase in computing power has allowed simulation of realistic cascade energies with good statistics and relatively long-time evolution of defects to be carried out. Second, new experimental findings and corresponding theoretical calculations have allowed interpretation of a number of mechanisms and phenomena crucial for understanding and prediction of practically important radiation effects, such as void swelling, radiation growth, matrix hardening and plastic flow localisation. In this paper we review the most significant results in atomic-scale computer modelling related to these issues, mainly focusing on new achievements such as the formation of extended defect clusters, the dynamic properties of defect clusters, interaction between radiation defects and strengthening of material due to radiation defects.

Production of defects in supported carbon nanotubes under ion irradiation

Ion irradiation of individual carbon nanotubes deposited on substrates may be used for making metallic nanowires and studying effects of disorder on the electronic transport in low-dimensional systems. In order to understand the basic physical mechanisms of radiation damage production in supported nanotubes, we employ molecular dynamics and simulate ion impacts on nanotubes lying on different substrates, such as platinum and graphite. We show that defect production depends on the type of the substrate and that the damage is higher for metallic heavy-atom substrates than for light-atom substrates, since in the former case sputtered metal atoms and backscattered recoils produce extra damage in the nanotube. We further study the behavior of defects upon high-temperature annealing and demonstrate that although ions may severely damage nanotubes in a local region, the nanotube carbon network can heal such a strong localized damage due to defect migration and dangling-bond saturation. We also show that after annealing the residual damage in nanotubes is independent of the substrate type. We predict the pinning of nanotubes to substrates through nanotube-substrate bonds that appear near irradiation-induced defects.

Radiation damage, trapping and release of deuterium in diamond and HOPG-graphite

We report the research done on the radiation damage production in HOPG-graphite and diamond due to the implantation of deuterium ions and its relation to the trapping and release of deuterium in these materials. The radiation damage was estimated using Rutherford backscattering spectrometry in channelling geometry (RBS-c), while trapping and release processes were followed using the D( 3He,p)α nuclear reaction. The measured radiation damage is larger than TRIM.SP predictions in both materials. Deuterium-induced damage at low fluences shows similar annealing behaviour in HOPG and in diamond. Implanted deuterium shows similar trapping behaviour in HOPG and diamond, while the thermal release shows two regimes: at high fluences the release behaviour is similar in both materials, at low fluences only little deuterium is released from diamond up to 1100 K.

Atomic processes during damage production and defect retention

Fundamental atomic processes during production and retention of radiation damage in structural materials are reviewed. Firmly established damage mechanisms are outlined, and some of the major uncertainties exposed. Damage production under neutron and ion irradiation proceeds through the elementary step of collision cascade formation, with further modification of the nascent cascade structure by inter-, and intra-cascade interaction events. Under fusion neutron irradiation, single cascade damage production occurs within 10 ps in most metals, with spatial extent of several tens to hundreds of nano-meters. Damage accumulation takes place over much longer time and length scales, during which multiple cascades interact leading to further re-structuring of the incipient cascade. Areas which require further investigation are: (1) the mechanisms of vacancy cluster collapse at the cascade core; (2) the athermal nucleation of interstitial loops at the periphery; (3) the migration of interstitial atoms and clusters emanating from the cascade; (4) the replacement of the dpa with a more physical measure of damage retention; (5) cascade structure for high PKA energies (above 20 keV); and (6) Inter- and Intra-cascade interactions, (7) and finally, cascade dynamics in damaged materials at high dose.

Computer simulation of displacement energies for several ceramic materials

Displacement energies ( E d) are fundamental parameters controlling the production of radiation damage in materials, and as such, are useful for understanding and modeling the effects of radiation on materials. These energies are not easily determined experimentally for many ceramic materials. However, advances in computational methodologies and their application to ceramic materials provide a means to determine these energies in a number of materials of interest. Although computationally intensive molecular dynamics methods can be used to determine E d for the various cations and anions, energy minimization methods can also provide a more expedient means to obtain reasonable estimates of these energies. In this paper, the energy minimization code General Utility Lattice Program (GULP), which uses a Mott–Littleton approximation to simulate isolated defects in extended solids, is used to calculate displacement energies. The validity of using this code for these computations is established by calculating E d for several ceramics for which these energies are known. Computational results are in good agreement with the experimental values for alumina, MgO, and ZnO. Results are also presented for two ceramic materials, zircon and spinel, for which there are little or no experimental values yet available.

Damage accumulation during 11B +, 12C + and 14N + implantations in Si

In this work a contribution to the understanding of the mass and dose dependence of the radiation damage production in silicon for light mass ion implantation is presented. The as-implanted damage profiles in Si implanted at room temperature with 11B +, 12C + and 14N + to doses between 1 × 10 14 cm −2 and 2 × 10 16 cm −2 were measured. In the regime of low doses (< 1 × 10 15 cm −2) the accumulation damage increases with the square root of the dose (Φ). However, for higher doses (> 2 × 10 15 cm −2) the accumulated damage scales with Φ n , being n ≈ 1 for 11B + implantation, 1 < n < 2 for 14N + and n > 3 for 12C +. The higher rate of damage accumulation in carbon implantation is explained by the “chemical” effects associated with the presence of high C concentration in the implanted layer. Additional experiments to investigate the damage accumulation in Si containing a high C concentration were performed to obtain deeper insight on the involved mechanism.

Radiation damage in NaCl. III. Melting phenomena of sodium colloids.

We report measurements on the melting behavior of colloids produced in irradiated NaCl. With differential scanning calorimetry (DSC) several latent-heat peaks near the melting temperature of pure bulk sodium metal have been detected. It appears that the total latent heat in these peaks is an accurate measure of the amount of damage in the crystal. Peak temperature and shape provide more detailed information about the properties of the colloids. The different melting temperatures can be explained by differences in the typical sizes of the colloid, based on the theory for melting of small particles. This DSC technique provides a method to evaluate the production of radiation damage in detail without changing the properties of the damaged crystal.

Basic physics of radiation damage production

The basic physical processes underlying the production of displacement damage in irradiated solids are briefly discussed, including topics from nuclear, atomic, and solid-state physics. Following a general introduction, the concepts of elementary cascade theory are presented as a basis for intuitive descriptions of the damage process. Then the production of primary recoils, mainly by nuclear processes, is discussed in enough detail to prepare a basis for calculating the primary-recoil energy spectra in typical irradiation facilities. The slowing down of fast atomic particles in solids is next discussed as a basis for developing atomistic models of damage production. Finally, several aspects of damage production, as revealed by atomistic simulation models, are outlined.

Characteristics of implantation-induced damage in GaSb

The production and annealing of radiation damage in GaSb Ne-implanted at high energy are studied by transmission electron microscopy and Rutherford backscattering spectrometry in combination with the channeling technique. The anomalous swelling phenomenon of implanted GaSb, previously reported, is found to be related to the formation of voids and microtwins in the crystalline implanted layer. These defects appear when the introduced damage exceeds a critical amount and lead to the formation of a porous polycrystalline GaSb layer, whereas in most other III-V materials an amorphous layer is formed. Provided the swelling is avoided, there is a good recovery of the lattice upon rapid thermal annealing at 600 °C. Otherwise, a heavily perturbed layer remains, containing voids, dislocations and, at sufficiently high doses, polycrystalline GaSb. From previously published results, it is inferred that the InSb behavior towards radiation damage is similar to that of GaSb.

Radiation damage in NaCl: General model of nucleation and aggregation processes in doped NaCl

Abstract The model presented here offers an extensive description of the nucleation and aggregation processes in irradiated NaCl. In particular the effect of impurities on the production of radiation damage has been studied. As compared to theoretical models in the literature the approach shows the following refinements: (1) The nucleation behaviour for aggregation of primary defects is included. Dislocation loops are formed by consecutive trapping of H-centres at impurity sites. Colloid nucleation is described by the coagulation of F-centres into higher order clusters. With the proposed mechanism we are able to consider the effects of the mobility of the F- and H-centre and the stability of the clusters during the nucleation process. (2) The precipitation of molecular halogen centres near the dislocation lines results in a rapidly increasing recombination of F-centres at high damage levels. The production of colloid becomes less-than-linear and the amount of radiation damage approaches a saturation value...

Relevance of atomic collisions in low-dimensional structure physics

Ion-irradiation is employed routinely for the fabrication and analysis of electronic and optoelectronic materials structures. This includes species-dependent applications where the ion species is chosen for its electrical or chemical properties, such as: doping, alloying, and compound formation; and species-independent applications, where the choice of ion species is made out of convenience, such as: sputter etching, damage-induced electrical or optical isolation, compositional intermixing and ion-beam analysis. In all cases, radiation damage is an unavoidable consequence of the irradiation and plays a crucial role in determining the success of such processing. The radiation damage generated in semiconductor structures depends on many variables, including ion beam parameters such as: ion species, energy, fluence, and flux; and substrate parameters such as: substrate material, temperature and doping level. A basic understanding of these dependencies emerged early in the history of the subject but the details of radiation damage accumulation are extremely complex, even for the simplest of substrate materials; much remains to be understood. The problem is even more complex in multilayered, low-dimensional semiconductor structures, where a variety of different materials and multiple interfaces also influence the type, concentration and distribution of defects. This paper discusses the relevance of ion-irradiation to semiconductor materials processing and reviews recent experiments which have contributed further to our understanding or radiation damage production and its dependencies in such materials. The emphasis of the discussion is on the use of MeV ion-irradiation for damage-related device applications.

Defects in ion-implanted uranium nitride.

The production of radiation damage in ion-bombarded UN single crystals and its recovery upon thermal annealing were studied by means of ion channeling and transmission-electron-microscopy (TEM) techniques. The implantation was performed with doses ranging from 4\ifmmode\times\else\texttimes\fi{}${10}^{14}$ to 1\ifmmode\times\else\texttimes\fi{}${10}^{17}$ at./${\mathrm{cm}}^{2}$ of 500-keV Xe ions or 300-keV Kr ions. The shapes of channeling spectra are similar to those typical for ion-implanted metals. They exhibit continuously increasing dechanneling over the entire damaged layer without a damage peak. According to TEM observations the created defects persist in the form of small, irregular clusters. The most characteristic features of the damage development are increase of the distorted layer thickness and saturation of the damage content with increasing implantation dose, formation of the disordered surface region due to preferential sputtering (altered layer), and the presence of a dislocation network between distorted and virgin regions of a crystal. All these defects anneal out upon thermal treatment. Two important annealing stages located at 900 and 1300 K were observed. For the complete recovery annealing temperatures exceeding 1700 K are necessary.

The Yield of DNA Double-strand Breaks Produced Intracellularly by Ionizing Radiation: A Review

The mechanisms of radiation damage production are used to examine the following premises: (1) the number of DNA double-strand breaks per unit dose increases with dose; (2) cell type to cell type variations in yield of DNA dsb per dose occur. Two stages of damage production are identified as possible sources of damage yield modulation; numbers of OH. free radicals reacting with the target, and amount of chemical repair occurring on the target radicals. These factors are discussed in the light of the structures within which cellular DNA is packaged and the known rate constants for the reactions involved. It is concluded from our current knowledge that, in the presence of oxygen: (a) the number of DNA dsb is linearly related to dose, and (b) the yields of DNA damage per dose among cell types are constant. There is a caveat to the latter conclusion: the chromatin structure may be different in radiosensitive cell lines. In the absence of such a difference, variations in radiosensitivity with dose or with cell type are assigned to differences in repair speed and/or accuracy.

Ion-implantation-induced stress in glasses: Variation of damage mode efficiency with changes in glass structure

Ion implantation induces lateral stress in glass due to the volume dilatation in the implanted near-surface region. Cantilever-beam experiments allow these quantities to be measured as a function of fluence. For fused silica the stress data for various incident ions are found to scale with atomic collision energy deposition. In sharp contrast, Pyrex (alkali-borosilicate) glass, (1 − x)(Na, K) 2O· xB 2O 3·3SiO 2 glass, and a sodalime (microscope slide) glass, yield stress values which scale with energy deposition into electronic processes. More significantly, this mode of damage production is dominant for the nuclear waste glasses PNL 76-68 and SRP. The void space in fused silica allows room for displaced Si and/or O. For the complex alkali-containing silicates, the interstitial volume is restricted. In the latter case, the probability increases that permanent defects can be formed by ionization-induced bond-breaking and network relaxation. These data imply that alpha-particle ionization energy deposition may be an important factor in nuclear waste glass radiation damage production, but the magnitude of this contribution has not yet been evaluated.