Fast Electron Irradiation Research Articles

Comparative Analysis of the Irradiation with Medium Fluences of High-Energy Electrons and Pr Doping on the Fluctuation Conductivity of YBa2Cu3O7–δ Single Crystals

Medium-fluence fast electron irradiation (1019 e/cm2 to 1020 e/cm2) or the changes in the praseodymium concentration in the range of 0.0 ≤ z ≤ 0.5 on the excess conductivity of YBa2Cu3O7–δ single crystals ware investigated. These can lead to a wider range of the temperature interval of excess conductivity which narrows the interval of linearity in the ab plane. At fluences 0 ≤ Φ ≤ 6.5 × 1019 e/cm2, there was a threefold increase in the transverse coherence length ξc(0) with an increase in Φ of more than four times as the praseodymium concentration increased to z ≈ 0.42. The two-dimensional–three-dimensional (2D–3D) crossover point shifted upward in temperature. Conversely, to irradiation with low fluences (Φ ≤ 1019 e/cm2) or low praseodymium doping (z ≤ 0.39), irradiation with medium fluences or high praseodymium doping led to a non-monotonic dependence of ξc(0) on the irradiation fluence, with characteristic maxima at Φ~(7–8) × 1019 e/cm2 and z ≈ 0.42, likely due to the suppression of the superconducting characteristics.

EPR characteristics of radiation-induced defects in Ge-rich α-quartz

Electron paramagnetic resonance (EPR) in a synthetic Si0.975Ge0.025O2 single crystal of α–quartz structure has been studied. After fast electron irradiation previously studied and new Ge-related paramagnetic centers (PCs) have been recognized using computer simulation of the observed EPR spectra. Increasing radiation doses allow to distinguish four paramagnetic [GeO4/M+]0 centers AGeLi, CGeLi, DGeLi, and AGeNa as well as four oxygen-vacancy electron centers Ge Eˊ1, Ge Eˊ2, Ge(IV) and a new Ge(V) center. The selective UV bleaching and distinct thermal stability of different centers allow us to determine the spin Hamiltonian parameters for the Ge(V) center.

Effect of 10 MeV electron irradiation on polyimide composites for space systems

This paper presents the results from a study on the effect of 10 MeV electron irradiation on polyimide (PI)–tungsten oxide WO2 composites. The electron flux (fluence rate) was 3.5×1015 electrons cm−2sec−1. A single absorbed dose varied between 10−20kGy with the maximum total absorbed dose being 10MGy. The morphological, physicomechanical, and dielectric properties of the samples were studied before and after irradiation with fast electrons, at various accumulated doses. It was found that irradiation with electrons at the maximum dose leads to an increase in the roughness of the PI surface, with an increase in average roughness from 28 to 46 nm, and for the PI/WO2 composite the roughness is practically unchanged, from 55 nm pre-irradiation to 58 nm post-irradiation. Irradiation of PI with fast electrons increases its Vickers microhardness by 39%, while that of the PI/WO2 composite decreases by 10% post-irradiation. At a maximum absorbed dose of 10MGy, the dielectric constant PI decreases by almost 20%, while fast electron irradiation of the PI/WO2 composite has practically no effect on the dielectric constant.

Solid State Amorphization and Alloy Parameters for High Entropy Alloys

Fast electron irradiation can induce the solid-state amorphization (SSA) of many intermetallic compounds. The occurrence of SSA stimulated by fast electron irradiation was found in the Al0.5TiZrPdCuNi high-entropy alloy (HEA). The relationship between the occurrence of SSA in intermetallic compounds under fast electron irradiation and the empirical alloy parameters for predicting the solid-solution-formation tendency in HEAs was discussed. The occurrence of SSA in intermetallic compounds was hardly predicted, only by the alloy parameters of δ or ΔHmix, which have been widely used for predicting solid-solution formation in HEAs. All intermetallic compounds with ΔHmix ≤ -35 kJ/mol and those with δ ≥ 12.5 exhibit the occurrence of SSA. This implies that the intermetallic compounds with a largely negative ΔHmix value and a largely positive δ parameter are favorable for the occurrence of SSA.

Introduction rates of radiation defects in electron irradiated semiconductor crystals of n-Si and n-GaP

A study was made of the introduction rate of radiation defects ΔNdef/ΔD versus the fast electron irradiation dose (D) in semiconductor crystals of n-Si and n-GaP. We take the concentration of radiation defects concentration Ndef to be the difference between the carrier concentration of semiconductors before n0 and after irradiation n(D) at the dose D, delivered at room temperature. By application of an appropriate fitting function to the dose dependent curves of the Ndef(D), it was demonstrated that the empiric exponential law of the form Ndef=n0(1−exp(−D/D0)) gives the best agreement with the experimental data, irrespective of the electron energy and irradiation dose. D0 is the irradiation dose, at which the carrier concentration n(D) at a temperature T=300K decreases by a factor of e. The results showed that the formation of radiation defects in the samples studied is not a linear process and ΔNdef/ΔD are found to decrease exponentially with increasing irradiation dose, according to their particular character. Using the same fitting method, it was found that for certain samples, beyond a particular radiation dose level, the rate of carrier mobility versus radiation dose also decreased exponentially.

Stabilization of microhardness of hard alloy VK6 cutting plates modified by fast electrons by cryoprocessing

The study is devoted to the effect cryoprocessing has on the stabilization of VK6 (hard alloy) after irradiation with fast electrons with energy of 5 MeV. To investigate samples with a close microstructure characteristics, a measurement of a structure-sensitive property -- co-effective force -- was held. It was shown that the treatment of VK6 hard alloy with fast electron irradiation increases its microhardness by 30 % in comparison with the original samples without any irradiation. It was found out that the microhardness of VK6 hard alloy samples after treatment with fast electrons depends on the initial surface structure, so that polished samples have higher values of microhardness than samples which surface were ground. X-ray phase analysis made it possible to establish the difference between the structures of polished and ground surfaces of the VK6 hard alloy in a stressed state. It was also shown that the treatment with fast electrons irradiation with an energy of 5 MeV does not lead to the formation of new phases. To establish the consolidation of the effect of increasing the hardness of the irradiated materials, annealing of VK6 hard alloy samples at the temperature of 30–100 °C (on air) was held. Cryoprocessing allowed us to consolidate the effect of increasing microhardness of the surface (surface microhardness) and wear resistance after irradiation of the VK6 hard alloy. Ill. 5. Ref. 10.

Solid state amorphization of metastable Al0.5TiZrPdCuNi high entropy alloy investigated by high voltage electron microscopy

The phase stability of high entropy alloy (HEA), Al0.5TiZrPdCuNi, under fast electron irradiation was studied by in-situ high voltage electron microscopy (HVEM). The initial phase of this alloy quenched from the melt was dependent on cooling rate. At high cooling rates an amorphous phase was obtained, whereas a body-centered cubic (b.c.c.) phase were obtained at low cooling rates. By thermal crystallization of the amorphous phase b.c.c. phase nano-crystals were formed. Upon fast electron irradiation solid state amorphization (SSA) was observed in b.c.c. phase regardless of the initial microstructure (i.e., “coarse crystalline structure” or “nano-crystalline structure with grain boundaries as a sink for point defects”). SSA behavior in the Al0.5TiZrPdCuNi HEAs was investigated by in-situ transmission electron microscopy observations. Because the amorphization is very rarely achieved in a solid solution phase under fast electron irradiation in common metallic materials, this result suggests that the Al0.5TiZrPdCuNi HEA from other common alloys and the other HEAs. The differences in phase stability against the irradiation between the Al0.5TiZrPdCuNi HEA and the other HEAs were discussed. This is the first experimental evidence of SSA in HEAs stimulated by fast electron irradiation.

Evaluation of the Effect of Different Doses of Fast Electron Irradiation on the Flavoring Compounds and Storage Life of Pink Garlic (Allium sativum L.)

Evaluation of the Effect of Different Doses of Fast Electron Irradiation on the Flavoring Compounds and Storage Life of Pink Garlic (Allium sativum L.)

Optical Properties of Natural and Synthetic Minerals

The results of investigation of optical absorption and photoluminescence (PL) of topaz, beryl and yttrium aluminium garnet crystals doped with different concentrations of transition ions exposed to fast neutron irradiation and electron irradiation are presented. We suppose that irradiation leads to the formation of two types of complex centers: "Me2+-F+ (or F) centre" and complex centers, which consist of a cation vacancy and an impurity (iron, manganese and chromium) ion. Exchange interaction between radiation defects and impurity ions during neutron or electron irradiation gives rise to appearance of additional absorption and luminescence band broadening in investigated crystals.

In-situ TEM observation of structural changes in nano-crystalline CoCrCuFeNi multicomponent high-entropy alloy (HEA) under fast electron irradiation by high voltage electron microscopy (HVEM)

The structural changes induced in a CoCrCuFeNi multicomponent nano-crystalline high-entropy alloy (HEA) under fast electron irradiation were investigated by in-situ transmission electron microscopy (TEM) using a high voltage electron microscope (HVEM). A fine-grained face centered cubic (fcc) single phase was obtained in the sputtered specimens. The fcc solid solution showed high phase stability against irradiation over a wide temperature range from 298 to 773 K, and remained as the main constituent phase even when the samples were irradiated up to 40 displacement per atom (dpa). Moreover, the irradiation did not seem to induce grain coarsening. This is the first report on the irradiation damage in 5-component HEA under MeV electron irradiation.

Phase transition of sigma-CrFe under fast electron irradiation

ABSTRACTPreparation of a sigma-CrFe single-phase specimen was achieved by arc melting of pure Fe and Cr, cold rolling, and subsequent annealing at 973 K or 1073 K in vacuum. Cold rolling before annealing is effective for the annealing-induced formation of sigma-CrFe from the bcc solid-solution phase. The phase stability and the structural change from sigma-CrFe to a bcc solid-solution phase under fast electron irradiation were investigated by in situ transmission electron microscope (TEM) observation in the temperature range between 22 K and 473 K by using an ultra-high voltage electron microscope (UHVEM). The phase transition of sigma-CrFe by fast electron irradiation was found to occur at a particular temperature.

Irradiation damage in multicomponent equimolar alloys and high entropy alloys (HEAs).

To maintain sustainable energy supply and improve the safety and efficiency of nuclear reactors, development of new and advanced nuclear materials with superior resistance to irradiation damage is necessary. Recently, a new generation of structural materials, termed as multicomponent equimolar alloys and/or high entropy alloys (HEAs), are being developed. These alloys consist of multicomponent elements for maximizing the compositional entropy, which stabilizes the solid solution phase. In this paper, preliminary studies on the irradiation damage in equimolar alloys and HEAs by High Voltage Electron Microscopy (HVEM) are reported [1-4]. (1) ZrHfNb equimolar alloys [1, 2]A multicomponent ZrHfNb alloy was prepared by a co-sputtering process using elemental Zr, Hf, and Nb targets using an AJA International ATC 2000-V system. A single-phase bcc solid solution was obtained in the ZrHfNb alloy with an approximately equiatomic ratio of its constituent elements. The irradiation-induced structural change in the ZrHfNb equimolar alloys with the bcc solid solution structure was investigated by HVEM using the Hitachi H-3000 installed at Osaka University. The polycrystalline bcc phase shows high phase stability against irradiation damage at 298 K; the bcc solid solution phase, whose grain size was about 20 nm, remained as a main constituent phase even after the severe irradiation damage that reached 10 dpa. (2) CoCrCuFeNi HEAs [3]A single-phase fcc solid solution was obtained in a CoCrCuFeNi alloy. The microstructure of the alloy depended on the preparation technique: a nanocrystalline CoCrCuFeNi alloy with an approximately equiatomic ratio of its constituent elements was obtained by a co-sputtering process with multi-targets, while polycrystalline structures were formed when the arc-melting method was used. Both nanocrystalline and polycrystalline structures showed high phase stability against fast electron irradiation at temperatures ranging from 298 K to 973 K; a fcc phase remained as the main constituent phase over 40 dpa of irradiation. The grain coarsening of the crystalline phase can be seen during the annealing in a nanocrystalline CoCrCuFeNi alloy, while the irradiation-induced grain coarsening did not occur at 773 K as well as at 298 K.

Phase stability of σ-CrFe intermetallic compound under fast electron irradiation

The phase stability of the σ-CrFe intermetallic compound under fast electron irradiation was studied using high-voltage electron microscopy. Under MeV electron irradiation within the temperature range of 298–473K, the σ phase does not maintain its original structure, but instead transforms into a body-centered cubic solid solution. No changes in the topological structure are observed at temperatures below 103K. This temperature dependence of the phase stability in σ-CrFe exhibited the opposite tendency to that of solid-state amorphization. The dominant factor affecting the phase stability was discussed in terms of the Gibbs free energy and the microstructural changes associated with the thermally assisted, radiation-enhanced migration of defects and/or constituent atoms.

Solid-state amorphization in a Ti2Pd intermetallic compound under fast-electron irradiation

MeV electron irradiation-induced structural changes in a C11b–Ti2Pd intermetallic compound were investigated by high-voltage electron microscopy to provide evidence for amorphous-phase formation in Ti-based (Ti>50at.%) intermetallic compounds. The Ti2Pd compound could not maintain its original structure against the MeV electrons, and a bct solid–solution phase was formed at 22, 103, and 298K. At temperatures ⩽103K, halo rings appeared in the selected area diffraction patterns after the bct-phase formation under the irradiation. This fact suggests the occurrence of solid-state amorphization; however, an amorphous single phase could not be obtained in the Ti66.7Pd33.3 alloy.

Annealing kinetics of boron-containing centers in electron-irradiated silicon

The annealing kinetics of B i O i pairs created by fast-electron irradiation in Si wafers is studied. The wafers are grown by the Czochralski method and doped with boron to different levels. It is found that, at a particular temperature, the annealing rate steadily increases with increasing boron concentration. The results are described with a simple model that takes into consideration the interaction of interstitial boron atoms with oxygen atoms and substitutional boron atoms. In the context of the model, the temperature dependence of the dissociation rate of the B i O i complex is calculated.

Optical Properties of Irradiated Yttrium Aluminum Garnet

The results of investigation of the photoluminescence (PL) and optical absorption of crystals Y3Al5O12(YAG) doped with different concentrations of manganese ions exposed to fast neutron irradiation and electron irradiation are presented. Photoluminescence spectra of YAG before neutron irradiation at T=80 K contain fine lines in orange region of spectrum, ascribed to Mn2+ ions in octahedral position. After irradiation band broadening is observed in the luminescence spectra of garnet crystals. Electron irradiation produced broad band with a complex structure related to Mn4+ ions. Exchange interaction between radiation defect and impurity ions during neutron irradiation and electron irradiation leads to appearance of additional lines and luminescence bands broadening in investigated crystals.

Accumulation of radiation defects and products of radiolysis in lithium orthosilicate pebbles with silicon dioxide additions under action of high absorbed doses and high temperature in air and inert atmosphere

One of the technological problems of a fusion reactor is the change in composition and structure of ceramic breeders (Li4SiO4 or Li2TiO3 pebbles) during long-term operation. In this study changes in the composition and microstructure of Li4SiO4 pebbles with 2.5wt% silicon dioxide additions, fabricated by a melt-spraying process, were investigated after fast electron irradiation (E=5MeV, dose rate up to 88MGyh−1) with high absorbed dose from 1.3 to 10.6GGy at high temperature (543–573K) in air and argon atmosphere. Three types of pebbles with different diameters and grain sizes were investigated. Products of radiolysis were studied by means of FTIR and XRD. TSL and ESR spectroscopy were used to detect radiation defects. SEM was used to investigate structure of pebbles. Experiments showed that Li4SiO4 pebbles with a diameter of 500μm had similar radiation stability as pebbles with diameter <50μm which were annealed at 1173K for 128h in argon and air atmosphere. As well as determined that lithium orthosilicate pebbles with size 500 (1243K 168h) and <50μm (1173K 128h) have a higher radiation stability in air and argon atmosphere than pebbles with size <50μm (1073K 1h). Degree of decomposition α10.56 of the lithium orthosilicate pebbles at an absorbed dose of 10.56GGy in air atmosphere is 1.5% and 0.15% at irradiation in dry argon. It has been suggested that changes of radiation stability of lithium orthosilicate pebbles in air atmosphere comparing with irradiated pebbles in argon atmosphere is effect of chemical reaction of lithium orthosilicate surface with air containing – H2O and CO2 in irradiation process. As well as it has been suggested that silicon dioxide – lithium metasilicate admixtures do not affect formation mechanism of radiation defect and products of radiolysis in lithium orthosilicate pebbles.

Magnetic-field-induced retardation of the recombination of nonequilibrium charge carriers in semiconductors

The retardation of the recombination of electrons and holes in semiconductors in an applied uniform magnetic field has been predicted. It has been shown that the recombination time in germanium in the temperature range of T = 1–10 K at charge carrier densities of n e = 1010−1014 cm−3 in magnetic fields of B = 3 × 102−3 × 104 G can be more than two orders of magnitude larger than that at zero magnetic field. This means that, after creation of nonequilibrium charge carriers by their injection at the p-n junction owing to some radiation sources or fast electron irradiation, the semiconductor retains its conductivity for a much longer time at nonzero applied magnetic field. The effect under study can be used, for example, to detect radiation sources.

Similarities and distinctions of defect production by fast electron and proton irradiation: Moderately doped silicon and silicon carbide of n-type

Effects of irradiation with 0.9 MeV electrons as well as 8 and 15 MeV protons on moderately doped n-Si grown by the floating zone (FZ) technique and n-SiC (4H) grown by chemical vapor deposition are studied in a comparative way. It has been established that the dominant radiation-produced defects with involvement of V group impurities differ dramatically in electron- and proton-irradiated n-Si (FZ), in spite of the opinion on their similarity widespread in literature. This dissimilarity in defect structures is attributed to a marked difference in distributions of primary radiation defects for the both kinds of irradiation. In contrast, DLTS spectra taken on electron- and proton-irradiated n-SiC (4H) appear to be similar. However, there are very much pronounced differences in the formation rates of radiation-produced defects. Despite a larger production rate of Frenkel pairs in SiC as compared to that in Si, the removal rates of charge carriers in n-SiC (4H) were found to be considerably smaller than those in n-Si (FZ) for the both electron and proton irradiation. Comparison between defect production rates in the both materials under electron and proton irradiation is drawn.

Biradical states of oxygen-vacancy defects in α-quartz: centers $$ E_{2}^{\prime \prime } $$ and $$ E_{4}^{\prime \prime } $$

Several new radiation defects with total electron spin S = 1 occurring in electron-irradiated, synthetic α-quartz have been observed by using electron paramagnetic resonance spectroscopy. These defects are considered to be biradicals, i.e., pairs of S = 1/2 species. The concentration of these centers depends on the condition of the fast-electron irradiation. They have different decay behaviors that allow measurements of any individual species especially when it predominates over the others. The primary spin Hamiltonian parameter matrices g1, g2, D have now been determined for two similar defects, which herein are labeled \( E_{2}^{\prime \prime } \) and \( E_{4}^{\prime \prime } \). Inter-electron distances estimated by using the magnetic dipole model, suggest that the structures of centers \( E_{2}^{\prime \prime } \) and \( E_{4}^{\prime \prime } \) both involve the unpaired electrons each located in orbitals of two silicon atoms next to a common oxygen vacancy but which have slightly different Si–Si distances at 0.90 and 0.79 nm, respectively. This model is consistent with previous DFT calculations of the triplet configurations with local energetic minima. Observed decay behaviors suggest a transformation of centers \( E_{2,4}^{\prime \prime } \) to the analogous \( E_{1}^{\prime \prime } \) center. These triplet centers in quartz provide new insights into the structures of analogous defects in amorphous silica.