Formation Of Radiation-induced Defects Research Articles

Simulation of Ion Paths in the Target Material for the Injection Complex of the BELA Facility

To realize the simulation experiments with the use of two ion beams at the injection complex of the BELA accelerator (Based on ECR ion source Linear Accelerator), it is necessary to determine the energy and irradiation angle of the beam of light ions which will be implanted into the region of radiation damage induced by heavy-ion beam. The depth of light-ion implantation is determined by the energy and kind of particles initiating the damage, as well as by their incidence angle. It is supposed that the incidence direction of heavy ions will coincide with the normal to the specimen surface. In our work, the necessary implantation zone for the iron ion beam with an energy of 3.2 MeV is located at depths of 300–800 nm. The simulation of the hydrogen and helium ion paths in the material of the iron target in the energy range from 150 to 600 keV at the angle to the normal from 0° to 65° is performed. The range of energies and irradiation angles for the hydrogen and helium ions are determined for the implantation into the radiation-induced defect-formation zone.

Effects of Proton Irradiation on Microstructure and Mechanical Properties of Nanocrystalline Cu-10at%Ta Alloy

Duplex nanocrystalline Cu-10at%Ta is attractive for extreme environments because of its grain size stability at high homologous temperatures, owing to dispersed Ta nanoclusters. This study is an initial investigation into the microstructural and mechanical stability of Cu-10at%Ta under irradiation. Proton irradiation is carried out to 1 displacement per atom (dpa) at 500°C. The Cu-10at%Ta exhibits grain size stability throughout irradiation and resistance to the formation of irradiation-induced defects. However, Ta nanoclusters undergo ballistic dissolution. Nanoindentation reveals there is no significant irradiation hardening, consistent with the relatively irradiation-stable microstructure. Ballistic dissolution of Ta nanoclusters is discussed in the context of Orowan strengthening.

Dependence of the Kinetics of Radiation-Induced Defect Formation on the Energy Absorbed by Si and SiC when Exposed to Fast Charged Particles

The kinetics of the formation of radiation-induced defects in silicon and silicon carbide as a function of the absorbed energy is analyzed. The dependence of the concentration of conduction electrons n-Si and n-SiC on the irradiation dose is studied experimentally under conditions of irradiation with electrons with an energy of 0.9 MeV and protons with an energy of 15 MeV. The advantages and disadvantages of using the integral flux (fluence) and absorbed energy as kinetic parameters are discussed. It is established in the performed studies that the visual representation of the kinetics of radiation-induced defect formation as a function of the fluence of irradiating particles is clearer for tabulating the requirements imposed to equipment stability under suitable conditions. To study the physical processes underlying the formation of radiation-induced defects in semiconductors, it is more convenient to use the dependences of the effects observed under radiation exposure as functions of the absorbed energy.

Fundamental Mechanisms for Irradiation-Hardening and Embrittlement: A Review

It has long been recognized that exposure to irradiation environments could dramatically degrade the mechanical properties of nuclear structural materials, i.e., irradiation-hardening and embrittlement. With the development of numerical simulation capability and advanced experimental equipment, the mysterious veil covering the fundamental mechanisms of irradiation-hardening and embrittlement has been gradually unveiled in recent years. This review intends to offer an overview of the fundamental mechanisms in this field at moderate irradiation conditions. After a general introduction of the phenomena of irradiation-hardening and embrittlement, the formation of irradiation-induced defects is discussed, covering the influence of both irradiation conditions and material properties. Then, the dislocation-defect interaction is addressed, which summarizes the interaction process and strength for various defect types and testing conditions. Moreover, the evolution mechanisms of defects and dislocations are focused on, involving the annihilation of irradiation defects, formation of defect-free channels, and generation of microvoids and cracks. Finally, this review closes with the current comprehension of irradiation-hardening and embrittlement, and aims to help design next-generation irradiation-resistant materials.

Degradation and regeneration of radiation-induced defects in silicon: A study of vacancy-hydrogen interactions

Silicon lattice vacancies exist in all silicon wafers, will increase in concentration due to high temperature processing, can form recombination active defects and have been proposed as a possible candidate for LeTID. Despite this, there have been relatively few studies in the solar field dedicated to investigating vacancies, their recombination properties or their interaction with hydrogen. In this work, we use high energy electron radiation to create large numbers of vacancies in silicon and study the lifetime response to subsequent thermal processes in the presence or absence of bulk hydrogen. The radiation results in the formation of radiation-induced defects which we interpret as being related to the creation of vacancies in the silicon bulk. Modelling of injection dependent minority carrier lifetime finds that the defects formed via this radiation process have different Shockley-Read-Hall properties to LeTID and are as such, unlikely to be related. Furthermore, this defect can be removed during low temperature annealing but only if hydrogen is present in the bulk of the silicon wafers. This is in contrast to samples with no bulk hydrogen which do not recover during low temperature annealing. The study thus finds no evidence for any link between LeTID and vacancies in silicon, but it does demonstrate the ability of hydrogen to repair radiation damage.

Changes in the Structure and Properties of Quartz Successively Implanted by Zn and F Ions during Thermal Annealing

The temperature dependences of structural and phase transformations in quartz successively implanted by zinc and fluorine during annealing in nitrogen have been studied. Plates were doped with 64Zn+ ions to a dose of 5 × 1016 cm–2 with an energy of 50 keV and then with 19F+ ions to the same dose but with an energy of 17 keV. After the implantation, individual Zn-containing particles about 100 nm in size were found on the sample surface. These particles decrease in size during annealing (by an order of magnitude after annealing at 800°C). The implantation leads to the formation of radiation-induced point defects and their clusters in the quartz bulk. Radiation-induced defects are gradually annealed during the heat treatment, and the phase of metallic zinc is transformed first to its zinc oxide (ZnO) at 600°C and then to willemite (Zn2SiO4) at 800°C.

Post-effects of radioactive decay in ligands on biologically active transport platforms

The electron capture consequences in the 57Co DOTA complex compound and processes of radiation-induced defect formation in DOTA under the effect of recoil nuclei produced after the α-decay of 241Am were studied using high performance liquid radiochromatography and emission Mössbauer spectroscopy. The experiments conducted have shown that the production of targeted RPHs on the base of alpha-emitters and when applying the conventional approach (biologically active molecular construct with any chelate carrying a radioactive tracer) is just a scientific mystification, since the recoiling alpha-emitting nucleus causes a destroying effect on the neighboring substrate molecules and entirely excludes the targeted transport of the preparation. This is a bold conclusion indeed. However, it is confirmed in part by the works of other authors and by the fact that the encapsulation of α-particle emitters in inorganic (rather than organic) nanocontainers significantly decreases the negative effect of recoil nuclei on the carrier molecule and allows radiation treatment to be done of cancerous tissues, which is similar to hadron therapy. It is the recoiling nuclei (and not at all the emitted alpha-particles) that possess a huge destroying ability and exert a therapeutic effect when conventional approach (biologically active molecular construct with any chelate carrying a alpha-emitters) are used. The amount of radiation-induced damage in a matrix, caused by a recoil nucleus with a typical energy of approximately 100 keV is by a factor of several hundreds higher than the amount caused by the 5–7 MeV α-particles. If a labelled molecular construction has reached the tumor cell, there is no doubt in the “prioritative” action of recoil nuclei as compared to that of α-particles. However, the picture changes dramatically if the recoil impact “is blocked” at the location where an α-particle is emitted (e.g., in inorganic nanocontainers). A success in the development and production of pharmaceutical forms based on alpha-emitters is possible only when the pernicious influence of recoil nuclei is “blocked” owing to a high radiation stability of labelled compounds or owing to other “means of transportation” of the radionuclides to lesions. A reasonable alternative to alpha-emitters might be Auger- and internal conversion electron emitters that possess (as it is shown by the present studies and, which is of more importance, by the worldwide radionuclide practice) by incomparably higher radiation stability of labelled compounds.

Transformation and Formation of Radiation-Induced Point Defects in Irradiated Lithium Fluoride Crystals After Their Mechanical Fragmentation

Changes in the concentrations of ordinary radiation defects and formation of near-cluster radiation defects (color centers) are shown to occur in nanocrystals fabricated by mechanical fragmentation of irradiated LiF crystals. Concentrations of near-cluster color centers increase to a steady value after fragmentation and remain constant at room temperature for a long time. UV irradiation of fabricated nanocrystals after termination of center formation processes in them causes the concentration of near-cluster defects containing three anion vacancies and two electrons to increase significantly. It is demonstrated that there are single-vacancy color centers as well as ordinary and near-cluster aggregate centers in unirradiated nanocrystals fabricated by fragmentation of unirradiated crystals.

Radiation stability of long-term annealed bi-phasic advanced ceramic breeder pebbles

Advanced ceramic breeder pebbles consisting of Li4SiO4 and additions of Li2TiO3 were tested regarding their long-term thermal and to their radiation stability. As-prepared and long-term annealed pebbles were irradiated with accelerated electrons (up to 6 MGy) to investigate the formation of radiation-induced defects and radiolysis products caused by ionizing radiation. By using Raman spectroscopy the formation of significant amounts of radiolysis products can be excluded. Electron spin resonance spectrometry revealed several paramagnetic radiation-induced defects, such as HC2 centres (SiO43- and TiO3-), E’ centres (SiO33- and TiO33-), Ti3+ centres and peroxide radicals (SiOO·). Radiation-induced defects forming in the first stage of the radiolysis seem to be more pronounced in long-term annealed samples. Thermally stimulated luminescence showed relatively low temperatures (40–200 °C) for the thermal recovery of the radiation-induced defects by accelerated electrons. Moreover, the main recovery process of defects takes place in the first 8–10 days after the irradiation.

Modifying the Structure of Multiwalled Carbon Nanotubes with Continuous and Pulsed Ion Beams

Changes in the local atomic and electronic structure and the chemical state of the surface of multiwalled carbon nanotubes (MWCNTs) irradiated with continuous and pulsed ion beams are studied using transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption near-edge spectroscopy. It is demonstrated that changes in the structure and the chemical state of MWCNTs under continuous irradiation with argon ions are attributable to the radiation-induced defect formation. When a pulsed carbon–proton beam is used, thermal effects exert a considerable influence on the structure of carbon nanotubes. The obtained results suggest that continuous and pulsed ion beams are suitable for targeted functionalization of physical and chemical properties of MWCNTs.

In situ TEM investigation of irradiation-induced defect formation in cold spray Cr coatings for accident tolerant fuel applications

The first in-situ ion irradiation and transmission electron microscopy (TEM) of cold spray deposited Cr coatings was performed at the Intermediate Voltage Electron Microscope (IVEM) facility at Argonne National Laboratory for preliminary investigation into the radiation damage tolerance of these materials for use in accident tolerance fuel cladding. The severely plastically deformed microstructure of the cold spray deposited Cr delayed the onset and growth of radiation induced defects when compared to an annealed coating simulating bulk Cr. Evidence to support this conclusion was based on defect density and defect size measurements of TEM images obtained at different irradiation intervals.

Effects of stacking fault energies on formation of irradiation-induced defects at various temperatures in face-centred cubic metals

ABSTRACTBy using the six sets of interatomic potentials for face-centred cubic metals that differ in the stacking fault energy (SFE) while most of the other material parameters are kept almost identical, we conducted molecular dynamics simulations to evaluate the effects of SFE on the defect formation process through collision cascades. The simulations were performed at 100, 300 and 600 K, with a primary knock-on atom energy of 50 keV. The number of residual defects is not dependent on the SFE at all the temperatures. For clusters of self-interstitial atoms (SIAs), their clustering behaviour does not depend on the SFE, either. However, the ratio of glissile SIA clusters tends to decrease with increasing SFE. This is because perfect loops, the edges of which split into two partial dislocations with stacking fault structures between them in most cases, prefer to form at lower SFEs. The enhanced formation of glissile SIA clusters at lower SFEs can also be observed even at increased temperature. Because most large vacancy clusters have stacking fault structures, they preferentially form at lower SFE; however, it is observed only at the lowest temperature, where the mean size increases with decreasing SFE. At higher temperatures, because of their extremely low number density, the vacancy clustering behaviour does not depend on the SFEs.

Effect of dose on irradiation-induced loop density and Burgers vector in ion-irradiated ferritic/martensitic steel HT9

ABSTRACTSamples of F/M steel HT9 were irradiated to 20 dpa at 420°C, 440°C and 470°C in a transmission electron microscope with 1 MeV Kr ions so that the microstructure evolution could be followed in situ and characterised as a function of dose. Dynamic observations of irradiation-induced defect formation and evolution were made at the different temperatures. Irradiation-induced loops were characterised in terms of their Burgers vector, size and density as a function of dose and similar observations and trends were found at the three temperatures: (i) both a/2 <111> and a <100> loops are observed; (ii) in the early stage of irradiation, the density of irradiation-induced loops increases with dose (0–4 dpa) and then decreases at higher doses (above 4 dpa), (iii) the dislocation line density shows an inverse trend to the loop density with increasing dose: in the early stages of irradiation, the pre-existing dislocation lines are lost by climb to the surfaces while at higher doses (above 4 dpa), the build-up of new dislocation networks is observed along with the loss of the radiation-induced dislocation loops to dislocation networks; (iv) at higher doses, the decrease of number of loops affects more the a/2 <111> loop population; the possible loss mechanisms of the a/2 <111> loops are discussed. Also, the ratio of a <100> to a/2 <111> loops is found to be similar to cases of bulk irradiation of the same alloy using 5 MeV Fe2+ ions to similar doses of 20 dpa at similar temperatures.

Effect of symmetrical and asymmetrical tilt grain boundaries on radiation-induced defects in zirconium

In this article, molecular-dynamics-based simulations were used to study the effect of grain boundaries (GBs) on the formation and spatial distribution of radiation-induced point defects. In order to perform this study, two sets of symmetrical and asymmetrical tilt grain boundaries were constructed along [0 0 0 1] and [0 −1 1 0] as the tilt axis, respectively. Vacancy, interstitial and Frenkel pair formation energies were estimated as a function of the distance from the GB core for both symmetrical as well as asymmetrical tilt GBs. The trend obtained between GB energies and point defect formation energies helps explain the biased absorption of interstitials over vacancies in most cases, as well as the equal absorption of both kinds of point defects in a few of them. It has already been reported from the experimental work that [0 0 0 1] GB structures closely resemble the polycrystalline texture of hcp materials, which motivates us to study the effect of irradiation on these GBs.

Модифицирование структуры многостенных углеродных нанотрубок с использованием непрерывного и импульсного ионных пучков

AbstractChanges in the local atomic and electronic structure and the chemical state of the surface of multiwalled carbon nanotubes (MWCNTs) irradiated with continuous and pulsed ion beams are studied using transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption near-edge spectroscopy. It is demonstrated that changes in the structure and the chemical state of MWCNTs under continuous irradiation with argon ions are attributable to the radiation-induced defect formation. When a pulsed carbon–proton beam is used, thermal effects exert a considerable influence on the structure of carbon nanotubes. The obtained results suggest that continuous and pulsed ion beams are suitable for targeted functionalization of physical and chemical properties of MWCNTs.

Irradiation-induced defect formation and damage accumulation in single crystal CeO2

The accumulation of irradiation-induced disorder in single crystal CeO2 has been investigated over a wide range of ion fluences. Room temperature irradiations of epitaxial CeO2 thin films using 2 MeV Au2+ ions were carried out up to a total fluence of 1.3×1016 cm−2 Post-irradiation disorder was characterized using ion channeling Rutherford backscattering spectrometry (RBS/C) and confocal Raman spectroscopy. The Raman measurements were interpreted by means of a phonon confinement model, which employed rigid ion calculations to determine the phonon correlation length in the irradiated material. Comparison between the dose dependent changes in correlation length of the Raman measurements and the Ce disorder fraction from RBS/C provides complementary quantitative details on the rate of point and extended defect formation on the Ce and O sub-lattices over a broad range of ion fluences. Raman measurements, which are significantly more sensitive than RBS/C at low doses, reveal that the nucleation rate of defects is highest below 0.1 displacements per atom (dpa). Comparison between Raman and RBS/C measurements suggests that between 0.1 and 10 dpa the damage evolution is characterized by modest growth of point defects and/or small clusters, while above 10 dpa the preexisting defects rapidly grow into extended clusters and/or loops.

Radiation sensitive detector based on field-effect transistors

The possibility of developing radiation detectors based on field-effect transistors (FET) is investigated. Transistor saturation current is chosen as an informative parameter for modeling. Experimental results show that the drain saturation current of the FET with p-n junction as a gate is decreasing after irradiation. In metal-oxide-semiconductor (MOS) FETs during radiation-induced defect formation two effects are competing, therefore the result of radiation influence is highly dependent on the electro-physical properties of transistors before irradiation and on the absorbed radiation dose. It is shown that saturation current increases with absorbed radiation dose for all the transistors with low electron concentration in a channel above certain levels of absorbed radiation. While the opposite effect is observed for high electron concentration in a channel, i.e. the saturation current drops. Obtained dependences of the drain saturation current of FET on the irradiation dose facilitated development of simple detector design for low levels of radiation. The bridge circuit is used in the radiation sensor to minimize the effect of temperature fluctuations. The sensitivity of the detector is enhanced several times with the help of two pairs of FETs with the opposite sign of radiation sensitivity.

Electron-beam charging of dielectrics preirradiated with moderate-energy ions and electrons

The effects of charging of dielectric targets irradiated with moderate-energy electrons in a scanning electron microscope are examined. Considerable differences in the kinetics of charging of the reference samples and the samples preirradiated with ions and electrons are reported. These differences are attributed to the processes of radiation-induced defect formation in Al2O3 (sapphire) and SiO2 that are, however, dissimilar in nature. The contributions of surface structure modification and changes in the electrophysical parameters of the surface (specifically, the charge spreading effect) are revealed. Critical doses of irradiation with Ar+ ions and electrons inducing active defect formation in dielectric targets and critical values of internal charge fields producing a significant contribution to the temporal parameters of Al2O3 and SiO2 charging are determined.

Radiation-Induced Defect Formation in Composite Materials and Their Destruction Under Electron Irradiation

With the example of polyimide films and their compositions with montmorillonite, the radiation damage and destruction of some composites is investigated. These composites should be assigned to the most radiation-resistant electroinsulating materials.

Characterisation and radiolysis of modified lithium orthosilicate pebbles with noble metal impurities

Modified lithium orthosilicate (Li4SiO4) pebbles with additions of titanium dioxide (TiO2) are suggested as an alternative tritium breeding ceramic for the European solid breeder test blanket module. The noble metals – platinum (Pt), gold (Au) and rhodium (Rh), can be introduced into the modified Li4SiO4 pebbles during the melt-based process, due to the corrosion of Pt-Rh and Pt-Au alloy crucible components. In this study, the surface microstructure, chemical and phase composition of the modified Li4SiO4 pebbles with different contents of the noble metals was analysed. The influence of the noble metals on the radiolysis was evaluated after irradiation with accelerated electrons (E=5MeV), up to 12MGy absorbed dose at 300–345K in a dry argon atmosphere. Using electron spin resonance (ESR) spectroscopy, it was determined that the noble metals (up to 300ppm) do not significantly influence the formation and accumulation of radiation-induced defects (RD) in the modified Li4SiO4 pebbles.