Formation Of Radiation Defects Research Articles

Radiation defect formation and effect on mechanical property in octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine investigated by molecular dynamics method

Energetic materials (EMs) are generally used in various conditions including under the neutron irradiation environment. To understand the radiation damages and related effects on mechanical property of EMs is important and necessary for their further applications under radiation conditions. In this paper, the displacement cascades are firstly simulated with molecular dynamics method in an octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) with the maximum energy of a primary knock-on atom (PKA) up to around 5 keV. The bond breaking, formation of free radicals, new gas molecules and interstitial and vacancy clusters, are all observed after displacement cascades, which can be used to explain the change of color and release of gas after irradiation as reported in experiments. Furthermore, the effect of above defect formation on mechanical property is calculated based on tensile stress simulations on damaged HMX. The results clearly show the appearance of strong stress gradient around defect formation region, resulting in lower external stress needed to deform the system. Thus, the radiation softening can be explored according to these results, same to experimental reports. Therefore, all these results indicate the radiation damages induced by energetic particles should be considered seriously for further application of energetic materials in nuclear conditions.

Radiation Effects in Tungsten and Tungsten-Copper Alloys Treated with Compression Plasma Flows and Irradiated with He Ions.

The paper presents the results of studying the structure and phase state of tungsten and tungsten-copper alloy after pulsed action of compression plasma flows and irradiation with helium ions. The compression plasma flows were used to modify the surface layer of tungsten, as well as to create an alloy based on tungsten and copper. Using scanning electron microscopy and X-ray structural analysis, the formation of radiation defects on the tungsten surface was detected in the form of local areas of exfoliation and destruction, which begin to form at helium ion irradiation doses of 2 × 1017 cm-2. It is shown that preliminary plasma treatment of the surface in the melting mode leads to the complete disappearance of surface radiation defects up to a dose of 2 × 1017 cm-2, which may be associated with the formation of a fine-crystalline grain structure, the intergranular boundaries of which serve as effective sinks for primary radiation defects.

Effect of Long-Range Interaction in the Modification of Surface Layers of WC–Co Samples by a Pulsed Ion Beam

The results of modification of WC–Co samples by a pulsed beam of nitrogen ions (200–300 keV, 120 ns) with an energy density of 7–8 J/cm2 are presented. It is shown that the change in the structure occurs in the near-surface layer with a thickness of 20–30 µm, which significantly exceeds the range of ions in the target (≈0.5 µm) and the depth of propagation of the thermal front during the pulse (≈1 µm). The analysis of various mechanisms of the long-range effect is carried out: the formation of a shock wave, the generation of primary radiation defects, etc. It is shown that the long-range effect is associated with the charge exchange of ions and the formation of fast atoms. The simulation of the charge exchange of ions in the gaseous layer of desorbed molecules is performed. It was found that the probability of ion charge exchange in the processes N+ + N2 → N0 and N+ + O2 → N0 significantly exceeds 100%, which indicates that the effect of irradiation by atoms was not taken into account while calculating. In contrast to ions, when the target is irradiated with atoms, the efficiency of the formation of radiation defects is much higher.

Threshold displacement energy map of Frenkel pair generation in [formula omitted]-Ga2O3 from machine-learning-driven molecular dynamics simulations

β-gallium oxide (β-Ga2O3) shows great promise for electronics applications, particularly, in future space operating devices exposed to harsh radiation environments for extended times. This study focuses on crucial, yet not fully explored, aspects of radiation damage in this material, such as threshold displacement energies and formation of various radiation-induced Frenkel pairs. Analyzing over 5,000 molecular dynamics simulations based on our machine-learning potentials, we conclude that the threshold displacement energies for two Ga sites, the tetrahedral (22.9 eV) and octahedral (20 eV) ones, differ stronger than the same values for three different O sites, which range only between 17 eV and 17.4 eV. Mapping of threshold displacement energies unveils significant differences in displacements for all five atomic sites. Our newly developed defect identification methodology successfully classified multiple Frenkel pair types in β-Ga2O3, with over ten different Ga and two primary O ones with a predominant O split interstitial at the O1 site. Finally, the calculated recombination energy barriers suggest that O Frenkel pairs are more likely to recombine upon annealing than Ga. These insights are pivotal for understanding the radiation damage and defect formation in Ga2O3, providing the basis for design of Ga2O3-based electronics with high radiation resistance.

Dosimetric studies of e-, γ-, n- Irradiation fields of the M-30 microtron (18.5 mev)

The results of the implementation and study of the radiation characteristics of high-energy electron (e-), gamma (γ-), and neutron (n-) radiation fields of the M-30 microtron with a maximum energy of 18.5 MeV are presented. Dosimetric characteristics were studied using the method of thermally stimulated luminescence (TSL) and using samples TLD-100H (LiF: Mg,Cu,P) and TLD-500K (Al2O3:C). Three e-, γ-, and n-experiments were performed at the same M-30 electron flux; the dosimetric indicators Yγ,n;e = Dγ,n/De, where Dγ,n is the intensity of the dosimetric peaks of TSL after γ- or n-irradiation, and De is, respectively, e-irradiation. We discuss the relative stability of these dosimeters' Yγ,e parameters at gamma irradiations and the presence of a partial correlation of Yn,e values in neutron fields. The latter is associated with the peculiarity of radiation defect formation in the material of dosimeters when interacting with nuclear particles of different types. The research results confirm the general ideas about the physics of electron radiation conversion into beams of nuclear particles of different natures. The data obtained are important in developing methods for dosimetric support of radiation technologies that use beams of mixed high-energy nuclear radiation, particularly for radiation therapy.

Paticularities of radiation defect formation in ceramic barium cerate

The results of the investigations are presented on the effect of irradiation with electrons, ions of inert gases (Ne, Ar, Kr) and oxygen on the structure and properties of Nd-doped barium cerate by the methods of X-ray diffraction analysis, scanning electron and atomic force microscopy, thermal desorption spectroscopy. It is shown that the low-energy irradiation with Ne and Ar ions stimulates the blistering processes on the surface, whereas the high energy ion irradiation by Ne, Ar, Kr ions the cerate surface undergoes the following stages of the spherulite growth - nucleation, growth (view of cauliflower), formation of spherulitic crust, correspondingly. The similar structures were not observed in the case of irradiation with high-energy oxygen ions. It is noticed that the irradiation of cerates with electrons leads to the formation of nano-sized acicular structures on the surface. The radiation of lowenergy ions of inert gases led to the conversion of most of the neodymium into a tetravalent state, as has been shown, accompanied by an increase in oxygen release and a decrease in water compared to non-irradiated cerate, as well as the independence of the amount of gases from the type of ions. Based on the data on thermal desorption of water and oxygen molecules from the irradiated barium cerate it was assumed that the irradiation stimulates the oxidation to Nd4+.

Formation of Radiation Defects in Wide-Band Semiconductors Based on Gallium (Ga2O3, GaN) under Proton Irradiation

Formation of Radiation Defects in Wide-Band Semiconductors Based on Gallium (Ga2O3, GaN) under Proton Irradiation

Radiation Defect Formation in a Silicon Carbide Betaconverter

Radiation Defect Formation in a Silicon Carbide Betaconverter

Математичне обґрунтування визначення віку четвертинних відкладів

The possibilities of applying the thermoluminescence method (TL-method) to investigate Quaternary sediments have been considered. The TL-method is used for dating in archaeology and geology. It was noted that this method covers larger age intervals than carbon dating. The TL-method is based on the measurement of the decay energy of natural radionuclides that are present in the rock. Therefore, the TL-method can be applied to the development of methodical and methodological issues of geochronology. Geochronological methods make it possible to date Quaternary sediments with a laboratory error of about five percent. Thus, it can be considered that the practical application of the thermoluminescence method for Quaternary sediments is highly important. This method provides a more detailed and accurate display of geochronological events. A new mathematical approach of age determination of Quaternary sediments applying the TL-method has been proposed. This new method can be applied for determination of the age of sediments and for conducting correlations between Neopleistocene sediments of remote regions. It has been noted that the TL-method of determination of the ‘absolute’ and relative age of Quaternary sediments is based on the properties of quartz crystals to accumulate energy of decay and to emit it during heating. It also was noted that quartz crystals as paleodosimeters can accumulate and preserve the age-related information for a long period of time. Quartz is the most common natural paleodosimeter. A mathematical formula for the age parameter has been proposed, using the energy that was accumulated by the investigated sample over time, the velocity of the formation of radiation defects, and the velocity of annihilation. The mathematical derivation of the formula for the age parameter is presented. The solution of the differential equation is described in detail. The proposed approach shows which sediments of an area are younger and which are older. It is emphasized that the proposed mathematical approach to the TL-method is effective for age determination of rocks, determining the sequence of the rock accumulation and for conducting correlation of different Quaternary sediments from different sections.

Effect of the Electron-Irradiation Temperature on the Formation of Radiation Defects in Silicon Carbide

Effect of the Electron-Irradiation Temperature on the Formation of Radiation Defects in Silicon Carbide

Atomistic Study for the Tantalum and Tantalum–Tungsten Alloy Threshold Displacement Energy under Local Strain

The threshold displacement energy (TDE) is an important measure of the extent of a material's radiation damage. In this study, we investigate the influence of hydrostatic strains on the TDE of pure tantalum (Ta) and Ta-tungsten (W) alloy with a W content ranging from 5% to 30% in 5% intervals. Ta-W alloy is commonly used in high-temperature nuclear applications. We found that the TDE decreased under tensile strain and increased under compressive strain. When Ta was alloyed with 20 at% W, the TDE increased by approximately 15 eV compared to pure Ta. The directional-strained TDE (Ed,i) appears to be more influenced by complex ⟨i j k⟩ directions rather than soft directions, and this effect is more prominent in the alloyed structure than in the pure one. Our results suggest that radiation defect formation is enhanced by tensile strain and suppressed by compressive strain, in addition to the effects of alloying.

ИМПУЛЬСНЫЕ ХАРАКТЕРИСТИКИ КРЕМНИЕВЫХ СТРУКТУР С N-P ПЕРЕХОДОМ, ОБЛУЧЕННЫХ ПРОТОНАМИ

Currently, methods are being actively developed to create semiconductor structures with desiredproperties by irradiation with ionizing particles (radiation defect engineering). The interactionof radiation defects with impurities, dislocations and other structural defects causes a change in theproperties of semiconductors and semiconductor devices. Irradiation with protons makes it possibleto controllably create radiation defects with a distribution maximum in a pre-calculated region. Theaim of this work is to analyze the effect of irradiation with low-energy protons on the impulse characteristicsof silicon structures with an n+-p junction. The task is to determine the effective lifetime  ofcharge carriers in the space charge region (SCR) of the n+-p junction. The n+-p-p+-structures madeof silicon grown by the Czochralski method, irradiated from the side of the n+-layer by a low-energyproton flux at sample temperatures of 300 K and 83 K were studied. To measure the impulse characteristics,bipolar rectangular voltage pulses with a constant amplitude of 10 mV and a frequency of1 MHz were used. The experimental data are explained using models of nonstationary charge carriertransport in inhomogeneous semiconductors and the formation of radiation defects in silicon underthe action of protons. Depth distributions of the average number of primary radiation defects arecalculated: interstitial silicon, vacancies, divacancies created by one proton per unit length of theprojective path. It is shown that irradiation with protons with a dose of 1015 cm2 and an energy of40 keV does not change the value of , but with an energy of 180 keV creates a region with an effectivelifetime of 5.5108 s in the SCR of the n+-p junction.

Radiation effects in Gd3(Al,Ga)5:O12:Ce3+ single crystals induced by swift heavy ions

Radiation effects in cerium doped Gd3(Al,Ga)5:O12 (or GGAG) single crystals irradiated by swift heavy ions with fluences ranging from 6·1010 to 2·1012 ions/cm2 have been studied. A stable strong induced absorption observed in the spectral range 200–350 nm correlates with the irradiation fluence. It is suggested that several centers are responsible for this induced absorption in GGAG single crystals and their possible origin (F-type centers and V-centers or holes trapped near cation vacancies) is proposed and discussed. The swift heavy ions irradiation strongly modifies the luminescence properties of GGAG, namely, the excitation spectra of the Ce3+ emission, which have been measured over a wide spectral range including vacuum ultraviolet diapason. In particular, it was shown that the formation of the stable radiation defects under swift heavy ions irradiation leads to the effective Ce4+ → Ce3+ transformation in the Mg2+ co-doped GGAG single crystals. The reasons leading to the alteration in the luminescence properties of irradiated GGAG single crystals are elucidated and discussed.

Investigation of the nature of polypropylene absorption bands before and after electron irradiation

The results of studies of reflection spectra in the UV, visible and near IR spectral regions for polypropylene films before and after electron irradiation (E = 30 keV, F = 1...3·1016 cm−2) are presented. The spectra were recorded in high vacuum at the irradiation site (in situ). Before irradiation, bands at 1200, 1400 and 1700 nm, caused by overtones of vibrational frequencies of CH, CH2 and CH3 molecular groups, and sorbed OH groups, were recorded. After irradiation and decomposition of the spectra into components, the absorption bands of the following radicals were detected: C3H5 –, – C3H6 –, – C4H6 –, – C4H7 –, – C4H8–, – C4H12 –, – C5H7 –, and – C5H10 –. A linear dependence of the energy position of absorption bands on the mass of the radicals that determine these bands was confirmed. The contribution of each band to the integral absorption band of a complex shape and its dependence on the electron fluence were determined. The mechanism behind the formation of radiation defects during irradiation of polypropylene is proposed.

Influence of Ion Irradiation on Critical Characteristics of Second-Generation HTSC Tapes

One of the practical applications of the second-generation HTSC tapes (or CC – coated conductors) is in accelerator magnets. During operation, the superconducting winding will inevitably be exposed to ionizing radiation with the formation of radiation defects in the HTSC layer. This process can lead to a gradual degradation of both the critical characteristics and the structure of the HTSC. The report presents the results demonstrating the change in the critical temperature and critical current (down to a complete loss of superconducting properties) of the second-generation HTSC tapes under irradiation with 6.3 MeV Cu ions in a wide range of fluences. The critical temperature was measured by a four-contact method. The critical current was calculated from the magnetization curves, which were measured in the temperature range from 5 to 77 K and magnetic fields up to 8 T. It was demonstrated that the critical current is more sensitive to radiation defects than the critical temperature is.

Radiation damage during HRTEM studies in pure Al and Al alloys

Abstract During transmission electron microscopy (TEM) investigations of Al alloys, defects caused by the electron irradiation can occur. Since the image contrast of these irradiation defects is similar to that of early stages of precipitates, care is needed to avoid confusion. In the present paper the formation and the coarsening of radiation damage defects were studied by in situ TEM in both, pure Al and Al alloys. High-resolution (HR)TEM images show on an atomic level that the radiation defects are extrinsic Frank loops (some converted into unfaulted prismatic loops); they are distributed homogeneously within the TEM foil but inhomogeneously on the four {111} planes. Applying HRTEM imaging conditions, the minimum electron energy causing defects is found to be as low as 110 keV using a [110] beam direction. The results for pure Al are very similar to those of the Al alloys. Therefore, during HRTEM studies (using accelerating voltages > 100 kV) the formation of radiation defects seems inevitable; they can be distinguished from the early stages of precipitates if they lie on different planes.

Defect formation and bending properties in graphite under He atom implantation investigated by molecular dynamics method

The formation and evolution of radiation defects and their effects on bending property of a single graphite under low energy helium atom implantation have been studied at atomic scale through molecular dynamics simulations. Various simple interstitial and vacancy defects are observed during the implantation process, which is a function of incident energy and cross section of helium-carbon interaction. Large defects are observed after continuous helium atom implantations. The effects of incident energy on the density, size and distribution of defects are analyzed in detail. Furthermore, the kinetic evolution process of radiation defects at different annealing temperatures have also been simulated, including the migration, aggregation, transformation, coalescence, and self-healing. The large defect clusters, crossing several carbon layers, have been confirmed to be the primary reasons that affect the bending property of graphite. All these results provide a new understanding for further applications of graphite in nuclear reactors.

On the effect of etching with a focused Ga-=SUP=-+-=/SUP=- ion beam in the energy range 12-30 keV on the luminescent properties of the Al-=SUB=-0.18-=/SUB=-Ga-=SUB=-0.82-=/SUB=-As/GaAs/Al-=SUB=-0.18-=/SUB=-Ga-=SUB=-0.82-=/SUB=-As heterostructure

The effect of ion energy in a focused ion beam in the range 12-30 keV on the formation depth of nonradiative recombination centers during etching of the Al0.18Ga0.82As/GaAs/Al0.18Ga0.82As double heterostructure has been studied. It is shown that an increase in the ion energy leads to an increase in the concentration and propagation depth of radiation defects. It was found that during etching of focused ion beam with ion energies above 15 keV, the depth of formation of radiation defects exceeds 900 nm, which does not correspond to the calculations in the Stopping and Range of Ions in Matter. Keywords: focused ion beam, radiation defects, photoluminescence, annealing, AlGaAs/GaAs.

Influence of stress in epitaxial ferrite-garnet films on the processes of radiation defect formation and low-temperature aging of the ion-implanted layers

To study the effect of mechanical stresses on the defect formation processes in epitaxial garnet films and on the low-temperature aging of the implanted layer, YIG films of different thicknesses irradiated with B+ ions with an energy of 80 keV were used. The presence of elastic deformation energy, the magnitude of which depends on the film thickness, leads to differences in the disorder of the near-surface layers during ion implantation. After 15 years of low-temperature aging of ion-implanted ferrite-garnet films at room temperature, the appearance of all strain profiles becomes the same and does not depend on the thickness of the implanted films.

ВЛИЯНИЕ ПРИМЕСИ ГОЛЬМИЯ НА ПРОЦЕССЫ РАДИАЦИОННОГО ДЕФЕКТООБРАЗОВАНИЯ В n-Si

Effect of Holmium Impurity on the Processes of Radiation Defect Formation in n-Si