Radiation Damage Properties Research Articles

Molecular-dynamics-based characterization and comparison of the radiation damage properties of three polytypes of cubic BC3

Boron ($$\mathrm{B}^{10}$$)-based materials such as boron carbide ($$\mathrm{B}_4\mathrm{C}$$) are used in control rods of the nuclear reactors because of their high neutron capture cross section and resistance to thermal and chemical degradation. There is an interest to consider other materials that may serve this purpose. In particular, boron-doped diamonds are prospective candidates as they are known to have excellent mechanical strength. In this work, molecular dynamics (MD) simulations are used to characterize and compare the basic radiation damage properties of boron-doped diamond with the stoichiometric formula $$\mathrm{BC}_3$$. Only cubic structures of $$\mathrm{BC}_3$$ were considered since the experimentally synthesized structure (as per existing literature) was cubic. The basic radiation damage properties compared include threshold displacement energy, primary damage and defect cluster analysis. In addition, the propensity of the material to amorphize under radiation (RIA – radiation-induced amorphization) was also analysed. It was found that the three materials had very similar threshold displacement energies and hence responded to radiation damage in an identical manner. Furthermore, it was seen that none of them were as favourable as the commonly used $$\mathrm{B}_4\mathrm{C}$$, as all of them amorphized at lower doses. Consequently, it is concluded that $$\mathrm{BC}_3$$, while having excellent mechanical properties, may not have good radiation resistance.

Classical interatomic potential for quaternary Ni–Fe–Cr–Pd solid solution alloys

In this paper, we present a new quaternary interatomic potential for the NiFeCrPd system, which is an extension on the previous NiFeCr potential. Density functional theory is used to calculate the quantities to be fitted, with particular focus on the energetics of point defects with solutes, for the potential to be used towards understanding radiation damage properties. The potential thus will enable the modeling of multi-elemental solid solution alloys consisting of up to four elements. To test the potential, we have performed atomistic kinetic Monte Carlo simulations to investigate the effect of configurational entropy on the self-diffusion coefficients. The self-diffusion coefficients are found to increase with chemical complexity, contrary to the common postulation of sluggish diffusion in high entropy alloys (HEAs). In addition, we have performed molecular dynamics simulations to elucidate the effect of Pd on vacancy diffusion and clustering in pure Ni and binary alloys. In agreement with recent irradiation experiments, our simulations show that while large vacancy clusters, such as stacking fault tetrahedra, are formed in pure Ni, Ni–Fe and Ni–Cr systems, negligible vacancy clustering is observed in Ni–Pd systems, indicating a possible effect of Pd in reducing cluster sizes. We suggest that this potential will be useful for studying the defect evolution in multi-component HEAs.

The Effect of Proton and Carbon Irradiation on 4H-SiC 1700V MPS Diode Characteristics

Electronic properties of radiation damage produced in 1700 V 4H-SiC MPS diodes by proton and carbon irradiation were investigated and compared. 4H-SiC epilayers, which formed the lowdoped N-base of MPS power diodes, were irradiated to identical depth with 670 keV protons and 9.6 MeV C4+ ions. Results show that irradiation with both projectiles produces strongly localized damage (deep levels) peaking at ion’s projected range. Compared to protons, heavier carbon ions introduce more defects with deeper levels in the SiC bandgap and more stable damage. Radiation damage act as electron traps and compensates donor doping of the epilayer and decreases electron mobility. Forward voltage drop of irradiated diodes then sharply increases when the peak concentration of introduced acceptor levels donor doping. The effect of both the proton and carbon irradiation can be simulated using a simple model accounting only for one dominant electron trap.

Point defects in 4H–SiC epilayers introduced by neutron irradiation

Electronic properties of radiation damage produced in 4H–SiC by neutron irradiation and its effect on electrical parameters of Junction Barrier Schottky (JBS) diodes were investigated. 4H–SiC N-epilayers, which formed the low-doped N-base of JBS power diodes, were irradiated with 1MeV neutrons with fluences ranging from 1.3×1013 to 4.0×1014cm−2. Radiation defects were then characterized by capacitance deep-level transient spectroscopy, I–V and C–V measurement. Results show that neutron irradiation introduces different point defects giving rise to acceptor levels lying 0.61/0.69, 0.88, 1.03, 1.08 and 1.55eV below the SiC conduction band edge. Introduction rates of these centers are ranging from 0.64 to 4.0cm−1. These defects have a negligible effect on blocking and dynamic characteristics of irradiated diodes. However, the acceptor character of introduced deep levels and their fast introduction deteriorate diode’s ON-state resistance already at fluences exceeding 1×1014cm−2.

Asymmetry of radiation damage properties in Al–Ti nanolayers

Molecular dynamics (MD) simulations were employed with empirical potentials to study the effects of multilayer interfaces and interface spacing in Al–Ti nanolayers. Several model interfaces derived from stacking of close-packed layers or face-centered cubic {100} layers were investigated. The simulations reveal significant and important asymmetries in defect production with ∼60% of vacancies created in Al layers compared to Ti layers within the Al–Ti multilayer system. The asymmetry in the creation of interstitials is even more pronounced. The asymmetries cause an imbalance in the ratio of vacancies and interstitials in films of dissimilar materials leading to >90% of the surviving interstitials located in the Al layers. While in the close-packed nanolayers the interstitials migrate to the atomic layers adjacent to the interface of the Al layers, in the {100} nanolayers the interstitials migrate to the center of the Al layers and away from the interfaces. The degree of asymmetry and defect ratio imbalance increases as the layer spacing decreases in the multilayer films. Underlying physical processes are discussed including the interfacial strain fields and the individual elemental layer stopping power in nanolayered systems. In addition, experimental work was performed on low-dose (1016atoms/cm2) helium (He) irradiation on Al/Ti nanolayers (5nm per film), resulting in He bubble formation ∼1nm in diameter in the Ti film near the interface. The correlation between the preferential flux of displaced atoms from Ti films to Al films during the defect production that is revealed in the simulations and the morphology and location of He bubbles from the experiments is discussed.

Point Defects in 4H-SiC Epilayers Introduced by 4.5 MeV Electron Irradiation and their Effect on Power JBS SiC Diode Characteristics

Electronic properties of radiation damage produced in 4H-SiC by electron irradiation and its effect on electrical parameters of Junction Barrier Schottky (JBS) diodes were investigated. 4H‑SiC N‑epilayers, which formed the low‑doped N-base of JBS power diodes, were irradiated with 4.5 MeV electrons with fluences ranging from 1.5x1014 to 5x1015 cm-2. Radiation defects were then characterized by capacitance deep-level transient spectroscopy and C-V measurement. Results show that electron irradiation introduces two defect centers giving rise to acceptor levels at EC‑0.39 and EC‑0.60 eV. Introduction rate of these centers is 0.24 and 0.65 cm‑1, respectively. These radiation defects have a negligible effect on blocking and dynamic characteristics of irradiated diodes, however, the acceptor character of introduced deep levels and their high introduction rates deteriorate diode’s ON-state resistance already at fluences higher than 1x1015 cm‑2.

Radiation Defects Produced in 4H-SiC Epilayers by Proton and Alpha-Particle Irradiation

Electronic properties of radiation damage produced in 4H-SiC epilayer by proton and alpha particle irradiation were investigated and compared. 4H-SiC epilayers, which formed the low doped n-base of Schottky barrier power diodes, were irradiated to identical depth with 550 keV protons and 1.9 MeV alphas. Radiation defects were then characterized by capacitance deep-level transient spectroscopy and C-V measurements. Results show that both projectiles produce identical, strongly localized damage peaking at ion’s projected range. Radiation defects have a negligible effect on dynamic characteristic of irradiated 4H-SiC Schottky diodes, however acceptor character of introduced deep levels and their high introduction rates deteriorate diode’s ON-state resistance already at very low irradiation fluences.

Radiation Damage in Pyrochlore and Related Compounds

ABSTRACTThe radiation damage properties of synthetic pyrochlore-defect fluorite compounds containing lanthanides on the A-site and Ti, Zr, Sn, and Hf on the B-site have been studied extensively using Kr ion irradiation. Using statistical analysis, we show that the results can be quantified in terms of the critical temperature for amorphization, structural parameters, classical Pauling electronegativity difference, and defect energies. The best current model is able to predict the critical temperature to within about 80 degrees Kelvin. The model indicates that radiation tolerance is correlated with an increase in the X anion coordinate toward the value characteristic of the defect fluorite topology, a smaller unit cell dimension, and lower defect energies. Our analysis also demonstrates that radiation tolerance is promoted by an increase in the Pauling cation-anion electronegativity difference or, in other words, an increase in the ionicity of the chemical bonds. Of the two possible cation sites in ideal pyrochlore, the B-site cation appears to play the major role in bonding. This result is supported, for a subset of pyrochlore compounds, by ab initio calculations, which reveal a correlation between the Mulliken overlap populations of the B-site cation and the critical temperature.

Electron radiation damage in Cu(In,Ga)Se2 analysed in‐situ by cathodoluminescence in a transmission electron microscope

AbstractThis contribution describes the first results of a completely new approach to study in‐situ the radiation damage properties of semiconductors, particularly of Cu(In,Ga)Se2 thin solar films by cathodoluminescence in TEM. This method proved to be sensitive to the initial damage processes that occur on an atomic level and are thus inaccessible otherwise in the microscope. The in‐situ character of the investigation permits to analyze also the defect formation kinetics directly. We discuss the development of the cathodoluminescence spectra in dependence of electron dose and accelerating voltage for Cu(In1–xGax)Se2 with [Ga]/([Ga] + [In]) ratio x ranging from x = 0 to x = 1. The obtained results indicate that the films with equal Ga and In concentration are the least radiation sensitive ones. The voltage dependence of the damage rate indicates that the damage arises essentially due to displacement by electron knock‐on (in the voltage range 150–300 kV). The defect formation kinetics can be interpreted with a first model which is supported by annealing experiments. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Radiation Effects and Defects in Cubic Boron Nitride. A Promising Multifunctional Material for Severe Environment Conditions.

ABSTRACTCubic boron nitride (c-BN) is a synthetic material which exhibits exceptional physicochemical properties such as: hardness, thermal conductivity, thermo-chemical stability, semiconducting properties and radiations resistance. Such outstanding properties make it a promising multifunctional material for applications in extreme conditions, as those found in the outer space environment. Its further use for such applications requires, however, a much better understanding of the lattice defects and radiation damage properties. Here we present the results of multifrequency ESR studies concerning the native and radiation induced point defects in crystalline c-BN under irradiation with high intensity 1MeV electron beams.

Radiation Damage Study on Various Structural Refractory Alloys of a Multi-Purpose Reactor

Radiation damage properties of structural materials play a key role in design of a fusion–fission (hybrid) reactor. Refractory alloys offer a significant advantage of high neutron wall load capability under fusion neutron environment. In this study, main radiation damage parameters (displacement per atom (DPA) and helium production) on three different refractory alloys, namely W-5Re, TZM (Mo alloy) and Nb–1Zr used as structural material in a hybrid reactor were found. Neutron transport calculations were conducted with the aid of SCALE4.3 System by solving the Boltzmann transport equation with code XSDRNPM. The lowest radiation damage values were obtained for W-5Re alloy. Moreover, all investigated materials will require to be replaced frequently due to their radiation damage values during reactor life (~ 30 years).

A study of the optical and radiation damage properties of lead tungstate crystals

A study has been made of the optical and radiation damage properties of undoped and niobium doped lead tungstate crystals. Data were obtained on the optical absorbance, the intensity and decay time of the scintillation light output, and the radioluminescence and photoluminescence emission spectra. Radiation damage was studied in several undoped and niobium doped samples using /sup 60/Co gamma ray irradiation. The change in optical absorption and observed scintillation light output was measured as a function of dose up to total cumulative doses on the order of 800 krad. The radiation induced phosphorescence and thermoluminescence was also measured, as well as recovery from damage by optical bleaching and thermal annealing. An investigation was also made to determine trace element impurities in several samples.

Effects of particle size and shape on dimensional change during sintering: S. Masuhara, S. Kawai (Kobelco Metal Powder of America Inc, Seymour, Indiana, USA)

Electronic properties of radiation damage produced in 4H–SiC by neutron irradiation and its effect on electrical parameters of Junction Barrier Schottky (JBS) diodes were investigated. 4H–SiC N-epilayers, which formed the low-doped N-base of JBS power diodes, were irradiated with 1 MeV neutrons with fluences ranging from 1.3 × 1013 to 4.0 × 1014 cm−2. Radiation defects were then characterized by capacitance deep-level transient spectroscopy, I–V and C–V measurement. Results show that neutron irradiation introduces different point defects giving rise to acceptor levels lying 0.61/0.69, 0.88, 1.03, 1.08 and 1.55 eV below the SiC conduction band edge. Introduction rates of these centers are ranging from 0.64 to 4.0 cm−1. These defects have a negligible effect on blocking and dynamic characteristics of irradiated diodes. However, the acceptor character of introduced deep levels and their fast introduction deteriorate diode’s ON-state resistance already at fluences exceeding 1 × 1014 cm−2.

Composite materials for fusion applications

Ceramic matrix composites, CMCs, are being considered for advanced first wall and blanket structural applications because of their high-temperature properties, low neutron activation, low density and low coefficient of expansion coupled with good thermal conductivity and corrosion behavior. This paper presents a review and analysis of the hermetic, thermal conductivity, corrosion, crack growth and radiation damage properties of CMCs.

Slow component suppression and radiation damage in doped BaF/sub 2/ crystals

The scintillation and radiation damage properties of barium fluoride crystals doped with various rare earths have been studied in an attempt to develop a fast, radiation hard scintillating crystal with a suppressed slow component for use at high counting rates. The light output of doped BaF/sub 2/ samples was measured with a solar blind (CsTe) photomultiplier tube and compared with a standard bialkali phototube. For dopants showing strong slow component suppression, measurements were also made at elevated temperatures and indicate that additional suppression can be achieved by heating. Radiation damage was studied by measuring the light transmission before, during and after irradiation with /sup 60/Co gamma rays for doses greater than 10/sup 6/ rad. The results show that several dopants suppress the slow component, but only one, namely lanthanum, preserves the radiation hardness of undoped BaF/sub 2/. >

Radiation processes in halide crystals and glasses

Materials with wide bandwidth transparency from the ultraviolet into the infrared are increasingly in demand for new electrooptic devices, lasers and light guides to be used in optical communication. Since the variety of potential applications can require the operation of these systems under hostile environmental conditions such as radiation, it is necessary that an understanding of the radiation damage process be obtained through a careful study of various types of materials and radiation environments. The fact that halide materials are particularly sensitive to radiation through a radiolysis process makes it imperative that potential devices involving these materials be characterized as to their radiation damage properties. The purpose of this paper is to review the radiation damage mechanisms in halide crystals and glasses and to assess their usefulness for future optical device systems.

Properties of Cr-Mn austenitic stainless steels for fusion reactor applications

Austenitic stainless steels, in which nickel is partly or completely substituted by manganese accompanied by an addition of nitrogen, have been studied at JRC-Ispra. The work carried out so far was aimed to characterize Cr-Mn steels with respect to many properties relevant for a fusion environment, in order to assess the possible use of these steels as candidate materials for fusion reactors. This review includes results obtained on structural changes due to thermal treatment with and without plastic deformation. The mechanical behaviour, in a broad range of temperatures, is also discussed in function of different mechanical treatments (cold working). Furthermore, irradiation effects, swelling and phase stability, obtained by electron irradiations, are presented. The influence of lithium on corrosion, structural stability, intergranular penetration and tensile properties is described. Finally the neutronic performances of Cr-Mn steels are given with attention on radiation damage properties, composition changes, decay heat, induced radioactivity and effect on tritium breeding.

Properties of Cr-Mn austenitic stainless steels for fusion reactor applications

Austenitic stainless steels, in which nickel is partly or completely substituted by manganese accompanied by an addition of nitrogen, have been studied at JRC-Ispra. The work carried out so far was aimed to characterize Cr-Mn steels with respect to many properties relevant for a fusion environment, in order to assess the possible use of these steels as candidate materials for fusion reactors. This review includes results obtained on structural changes due to thermal treatment with and without plastic deformation. The mechanical behaviour, in a broad range of temperatures, is also discussed in function of different mechanical treatments (cold working). Furthermore, irradiation effects, swelling and phase stability, obtained by electron irradiations, are presented. The influence of lithium on corrosion, structural stability, intergranular penetration and tensile properties is described. Finally the neutronic performances of Cr-Mn steels are given with attention on radiation damage properties, composition changes, decay heat, induced radioactivity and effect on tritium breeding.

Über den einfluβ der ionenimplantation auf die geschwindigkeit der anodischen siliziumoxydation

In the present work we investigated the influence of implanted ions (dose = 10 16−10 17 cm -2, energy = 7.5−50 keV) of the 1st, 3rd, 4th, 5th, 6th, 7th and 8th main groups of the periodic table on the anodic oxidation rate of 〈111〉- oriented p-type silicon as a function of the vertical distance x from the surface. By means of a comparison of the distance x̄ m, which corresponds to the maximum or minimum of the anodic oxidation rate, with the mean projected range R p of implanted ions and by means of a comparison of unannealed with annealed samples the effect of implanted ions could be separated from the effect of radiation damage. An increase in the anodic oxidation rate of silicon was found after implantation of H +, C +, N +, Cl +, Ar + and Xe + ions. With the exception of silicon implanted with Ar + and Xe +, this effect is caused mainly by the implanted ions and is almost uninfluenced by radiation damage. A decrease in the anodic oxidation rate of silicon was observed after implantation of Al +, Ga + and Sb + ions. This is probably caused by radiation damage. Therefore radiation damage can decrease or increase (Ar +- and Xe +-implanted silicon) the anodic oxidation rate. This effect depends on the nature of the implanted ions which generated the radiation damage and may be caused by the different electrical properties of radiation damage caused by various ions.

The relationship between material properties and the economics of fusion power

Fusion power cost is Influenced by materials, fabrication costs and a large number of material properties that impact reactor performance and safety. Reactor performance parameters that are affected include thermal to electrical conversion efficiency, neutron wall loading (power density), availability, and plasma burn time. Chief among the material properties affecting the above reactor performance parameters are the material's temperature limit and the mechanical, thermal and radiation damage properties that determine life and reliability. Extensive materials testing will be required to satisfy a reliability goal of not more than one wall failure per year. Material properties may affect safety issues such as tritium inventory, waste disposal and coolant choice. Determination of the impact of material properties on the cost of fusion power is addressed. This determination is incomplete in some cases.