Generation Of Radiation Defects Research Articles

Influence of gamma radiation on magnetoelectric properties of extruded samples of solid solution Bi85Sb15〈Te〉 modified ZrO2

The electrical and thermal properties of extruded samples of Bi[Formula: see text]Sb[Formula: see text] [Formula: see text] modified with ZrO2 were investigated depending on the dose of gamma radiation in the temperature range [Formula: see text] K and magnetic field strength (H) [Formula: see text] A/m. It was found that an increase in the mobility in the irradiated modified Bi[Formula: see text]Sb[Formula: see text] [Formula: see text] is associated with the radiation introduction of acceptor (negatively charged) centers, which at low doses are generated mainly in the regions of the efficiency of impurity scattering of charge carriers and partially neutralized centers and, accordingly, to a certain increase in the mobility. In the extruded modified samples of the Bi[Formula: see text]Sb[Formula: see text] solid solution, irradiation with gamma quanta results not only in the generation of radiation defects (RDs) (centers), but also accompanied by their rearrangement. This causes a change in the spectrum of localized states and the electron scattering process, which leads to corresponding changes in the presented electrical and thermal parameters.

Hardness variation in nanocrystalline SiC irradiated with heavy ions

This study reports on the hardness of nanocrystalline silicon carbide (nc-SiC) with different grain sizes using nanoindentation technique. Both amorphous SiC (am-SiC) and single-crystal SiC (sc-SiC) are also investigated for a comparison study. Irradiation experiments were performed for the different types of SiC using Kr and Xe ions at elevated temperatures. It is found that the hardness of the am-SiC increases after Kr ion irradiation at 550 K, which is attributed to the irradiation-induced densification of the amorphous network structure. At higher temperatures (≥700 K), irradiation leads to crystallization of spherical nanograins in the am-SiC. The hardness values of the resulting nc-SiC with average grain sizes of ∼7 and 10.5 nm from the Kr and Xe ion irradiations, respectively, are found to be similar (∼40 GPa) and comparable to that of sc-SiC (38 GPa). In contrast, as-deposited SiC with a nano-columnar texture full of stacking faults (SFs) and twins exhibits super high hardness of 52.7 GPa, likely due to the suppression of the formation and propagation of indentation-induced dislocations in SiC. After Xe ion irradiation at 700 K, the hardness of the nano-columnar SiC decreases to 41.8 GPa, although the SF structure within the grains is well retained after irradiation. This is attributed to generation of radiation defects (such as invisible defect clusters) in the nano-columns, which could cause the hardness to decrease.

Photoluminescence of ion-synthesized 9R-Si inclusions in SiO2/Si structure: Effect of irradiation dose and oxide film thickness

The study of hexagonal silicon polytypes attracts special attention due to their unique physical properties compared to the traditional cubic phase of Si. Thus, for some hexagonal phases, a significant improvement in the emission properties has been demonstrated. In this work, the luminescent properties of SiO2/Si structures irradiated with Kr+ ions at different doses and annealed at 800 °C have been systematically investigated. For such structures, a photoluminescence line at ∼ 1240 nm is observed and associated with the formation of hexagonal 9R-Si phase inclusions. It is found that the variation in the thickness of oxide film and the relative position of ion distribution profile and film/substrate interface leads to a regular change in the luminescence intensity. The nature of the observed dependencies is discussed as related mainly to the interplay between the factors contributing to the formation of 9R-Si inclusions and the generation of radiation defects in the Si substrate—centers of nonradiative recombination. The revealed regularities suggest optimal ion irradiation conditions for synthesis of optically active 9R-Si phase in diamond-like silicon.

Effect of Segregation of Ni and Cr at Dislocation Loops on Their Interaction with Gliding Dislocations in Irradiated Fe−Ni−Cr BCC Alloys

Ferritic–martensitic steels alloyed with chromium and containing nickel impurities are considered as promising structural materials for nuclear and thermonuclear power engineering. During operation, the plastic properties of such materials degrade under the influence of neutron irradiation caused by the generation of radiation defects of the crystal structure, in particular, dislocation loops and new phases (precipitates). In this paper, an atomistic computer simulation of the interaction of mobile edge dislocations with dislocation loops having the 〈100〉 and 1/2〈111〉 Burgers vectors forming a single extended defect with Ni−Cr precipitates is performed using the classical molecular dynamics method at various temperatures (300 and 600 K). Such composite radiation-induced defects cause a change in the plastic properties of the irradiated material due to radiation hardening. The results of studying the interactions of gliding dislocations with loops (both in pure iron and in the Fe−Ni−Cr alloy, taking into account the precipitation of Ni and Cr at dislocation loops) show that the presence of an increased concentration of chromium and nickel atoms near the dislocation-loop perimeter at 300 K either decreases the critical stress for passing the dislocation through a defect (by more than 50 MPa) for the 〈100〉 loops at 300 K or increases it for the 1/2〈111〉 loops at 300 K. At a high temperature (600 K), the presence of Ni and Cr impurities near the dislocation loop leads to an increase in the critical stress for both types of loops. It is shown that the presence of an increased concentration of Ni and Cr atoms near the loop perimeter facilitates or hinders (depending on the specific dislocation-loop configuration) the transverse gliding of dislocation segments, complicates the possibility of the resplitting of junction segments of the dislocation and loop in the plane of loop location, and causes the immobilization of the loop having the [111] Burgers vector parallel to the gliding plane of the dislocation at 300 K.

Mechanical properties of carbon steel depending on the rate of the dose build-up of nitrogen and argon ions

The effect of pulsed irradiation with argons and nitrogen ions on the mechanical properties, mor� phology, and structure of the surface layers of carbon steel St3 (0.2% C, 0.4% Mn, 0.15% Si, and Fe for bal� ance) has been investigated depending on the rate of dose buildup at an average ion current density of 10, 20, and 40 μA/cm 2 . It has been established that the fatigue life and microhardness of surface layers increase in the entire studied range of dose buildup rates. This seems to be due to the hardening of the surface layers, which resulted from the generation of radiation defects and the irradiationdynamic effect of fast ions. The sample irradiated by argon ions at the lowest of the selected dose buildup rates j av = 10 μA/cm 2 withstands the largest number of cycles to failure.

Phosphorus-containing cesium compounds of pollucite structure. Preparation of high-density ceramic and its radiation tests

Multicomponent oxides of pollucite structure, containing Cs and Ba, were synthesized as powders and ceramics. Their chemical compositions, Cs[MgAl0.5P1.5O6] and Cs0.875Ba0.125[Li0.125Zn0.875Al0.5P1.5O6], were modeled on the basis of the known structural features, taking into account the principles of iso- and heterovalent isomorphism of cations. From powdered samples synthesized using sol-gel process, a ceramic was prepared by spark plasma sintering (SPS). The sintering time was 3–4 min in the temperature interval 600–850°C. The relative densities were 97 and 99%. To evaluate the radiation resistance of the ceramics, the samples were irradiated with 132Xe26+ ions (E = 167 MeV) in the fluence interval from 6 × 1010 to 1 × 1013 cm−2 (ion flux density ∼109 s−1 cm−2). The amorphization took place at fluences of (1.2–1.3) × 1012 cm−2. This fact suggests the decisive role of the ion energy loss for ionization in the generation of radiation defects. Conditions were found for the transition of the metamict form into the crystalline form on heating.

Ferromagnetism, paramagnetism, and thermally induced magnetism in photomagnetic CrIII/MnII and CrIII oxalates with the 7-methyl-3,3-diphenyl-3H-pyrano[3,2-f]quinolinium cation

Single crystals of the new cationic chromene, 7-methyl-3,3-diphenyl-3H-pyrano[3,2-f-quinolinium iodide (C25H20NO)I (1), were synthesized. The crystal structure of the new compound was studied, and quantum chemical calculation for the open and closed forms were carried out. The bifunctional compounds containing mono- and bimetallic 3d metal (tris)oxalates with the chromenium cation, (C25H20NO)3[Cr(C2O4)3] · 4H2O (2) and (C25H20NO)[CrMn(C2O4)3] · H2O (3), were prepared. Compound 1 is paramagnetic due to low-lying thermally excited states of the chromene molecules. At low temperatures (∼2 K), the paramagnetic states are frozen, and the compound becomes diamagnetic. Compound 2 is paramagnetic and its magnetic properties are determined mainly by the Cr3+ ions and the thermally induced paramagnetic states of the chromene molecules. At high temperatures, the magnetic moment of compound 3 consists of the contributions of the paramagnetic Cr3+ and Mn2+ ions and the thermally induced paramagnetic states of chromenes. At low temperatures (2–3 K), the thermally induced magnetism of organic molecules is frozen, and the magnetically ordered (and, probably, spin-glass) state is observed in the two-dimensional network of metal oxalates (Tc = 3 K in the zero magnetic field). The UV irradiation leads to an increase in the magnetic moment of the compound in the paramagnetic region due to the generation of radiation defects.

Irradiation-Induced Growth and Microstructure of Recrystallized, Cold Worked and Quenched Zircaloy-2, NSF, and E635 Alloys

Abstract This paper is devoted to the study of the effect of the texture, phase composition, and microstructure on the irradiation-induced growth strain (GS) of zirconium-based alloys. GS measurements and TEM microstructural examinations were performed on Zry-2, NSF, and E635 samples in the recrystallized, beta quenched and cold-worked (CW) conditions. The samples were irradiated in the BOR-60 reactor in the temperature range of 315–325°C up to a neutron fluence level of 1.1 ×1026 n/m2 (E>1 MeV), i.e., up to a damage dose of 23 dpa. Growth strains of NSF and E635 alloys in all states and in the longitudinal and transverse directions are lower as compared to those of Zry-2, and do not exceed 0.2 % even at the maximum fluence level. As for recrystallized Zry-2, the GS kinetics are characterized by the appearance of the accelerated growth stage. A combination of a certain amount of Nb, Fe, and Sn in the matrix content plays a key role in GS kinetics. The higher the degree of CW, the higher the irradiation growth but its rate of increase with increasing fluence is different for alloys of different compositions. The maximum GS, reaching 0.72 %, is observed in the 20 % CW Zry-2 samples. Texture, along with the alloy composition, is one of the main GS-determining factors. Irradiation growth of the transversal samples is lower as compared to the longitudinal ones because of texture. As for quenched alloys, the texture is practically isotropic and GS values are low, independent of the alloy composition. In CW materials, the density of <c>- dislocations greatly affects the irradiation growth strain. Particles of Zr(Fe,Cr)2 and Zr2(Fe,Ni) phases in Zry-2 as well as Zr(Nb,Fe)2 in NSF and E635 are depleted in iron under irradiation. The Fe goes into the matrix and modifies its properties. The HCP lattice structure in the Laves phases in NSF and E635 changes into BCC (β-Nb-type). FCC (Zr,Nb)2Fe precipitates preserve on the whole their composition and structure; no amorphization of the Nb-containing precipitates is observed. The Zr2(Fe,Ni) precipitates with a BCT lattice remain crystalline, and HCP Zr(Cr,Fe)2 precipitates undergo amorphization. The average particle size in the irradiated alloys is larger and the concentration is a little lower as compared to the unirradiated ones. Irradiation-induced fine dispersed precipitates about 3 nm in size, probably enriched in niobium, appear in NSF and E635. The observed changes of microhardness are discussed from the viewpoint of generation of radiation defects (clusters, dislocation loops), evolution of the initial dislocation structure, and matrix composition (enrichment in Fe, Cr, and, probably, Nb).

Radiation Defects and Thermal Donors Introduced in Silicon by Hydrogen and Helium Implantation and Subsequent Annealing

The effect of high-energy hydrogen and helium implantation and subsequent annealing on generation of radiation defects and shallow donors in the low-doped oxygen-rich FZ n-type silicon was investigated. Samples were implanted with 7 MeV 4He2+ or 1.8 MeV 1H+ to fluences ranging from 1x109 to 3x1011 cm-2 and 1.4x1010 to 5x1012cm-2, resp., and then isochronally annealed for 30 minutes in the temperature range up to 550°C. Results show that radiation damage produced by helium ions remarkably enhances formation of thermal donors (TDs) when annealing temperature exceeds 375°C, i.e. when the majority of vacancy-related recombination centers anneals out. The excess concentration of TDs is proportional to the helium fluence and peaks at 1.6x1014cm-3 if annealing temperature reaches 475°C. Proton irradiation itself introduces hydrogen donors (HDs) which form a Gaussian peak at the proton end-of-range. Formation and annealing of shallow and deep hydrogen-related levels are strongly influenced by electric field at annealing temperatures below 175°C. If annealing temperature exceeds 350°C, HDs disappear and the excessive shallow doping is caused, as in the case of helium irradiation, by radiation enhanced TDs.

Promotion of metallurgical reactions at the Ni-SiC interface by irradiation with protons

It is shown that irradiation of Ni-SiC structures with protons at elevated temperatures promotes metallurgical reactions at the Ni-SiC interface owing to a diffusion mechanism stimulated by the generation of radiation defects. The most pronounced effect of mixing at the metal-semiconductor interface is observed if the thickness of the metal film is equal to the projected range of protons.

Formation of shallow donors and acceptors in silicon irradiated with either electrons or high‐energy ions and annealed at temperatures of 400–700 °C

The formation of electrically active shallow centers in electron-irradiated (the case of uniform generation of radiation defects) silicon and crystals implanted with high-energy ions (non-uniform generation of radiation defects) under annealing at temperatures of 400–700 °C was investigated. Non-uniform generation of thermal donors and thermal acceptors was found for both cases at 450 °C. Formation of domains with p- and n-type conductivity was observed in the electron-irradiated silicon.

Study of thermal properties of electron irradiated metallized polyimide films

The paper presents the results of experiments on the temperature dependence of thermal conductivity and heat capacity of some metallized polyimide films irradiated with electrons of energy 2–6 MeV. Accelerator ALU-6 was used to irradiate films with different integral doses (0–2×10 −3 Gy). A cascade-probability model of generation of radiation defects in polymers (break of polymer chains) was developed. Such defects act directly on the process of heat transport and heat capacity.

On the generation of radiation defects by accelerated ions in silicon

The introduction of centers of generation of charge carriers in pure Si is examined in the framework of the interaction of nonequilibrium defects and charge carriers directly in the track of an ion. An experiment on a particles with energies of 1.0–5.0 MeV is supplemented by the results of a numerical simulation of the stopping of such particles in Si. It is shown that the primary defects arising at the end of the track form a smaller number of generation centers. This is explained by the trapping of components of Frenkel pairs of charge carriers, the concentration of which in the track undergoes a 3-fold increase by the end of the range. Charge exchange between vacancies and interstitial atoms both accelerates recombination and lowers the number of primary defects participating in the subsequent complex-formation.

Silicon microstrip detector radiation damage by 1.5 MeV electrons and synchrotron radiation

Abstract We have investigated the radiation hardness of silicon microstrip detectors by exposing them to 1.5 MeV electrons and synchrotron radiation, respectively. For 1.5 MeV electrons the observed effects can be explained by the generation of radiation defects in the bulk part of silicon. We have determined the damage constant, the leakage current increase and also different threshold doses, above which essential detector parameters (electronic noise, stability of dc-coupled readout electronics, charge collection efficiency) are getting influenced by the radiation damage.

Stimulation of sorption on metal films by means of radiation defects

In the present work the parameters characterizing sorption processes on irradiated surfaces are discussed. The hypothesis of a stimulating effect due to radiation defects on the sorption processes is confirmed by measuring the sticking coefficient. The sorption of nitrogen on titanium films (at 300 K) under helium, argon, neon, krypton and N 2 ion bombardment is investigated. The bombardment of the surfaces with ions with energies up to 1.5 keV results in a significant increase in the sticking coefficient. The dependences of the sticking coefficient and the sorption ratio on the parameters of the radiation are shown and a good correlation between the increase in the sorption ratio and the rate of generation of radiation defects is found.

Generation of radiation defects in KCl by high-frequency discharge in hydrogen: A I Bazhin and A I Dudelzak,Phys Process in Crystal with Defects, Coll, Kiev 1972, 203–206 ( in Russian)

Generation of radiation defects in KCl by high-frequency discharge in hydrogen: A I Bazhin and A I Dudelzak,Phys Process in Crystal with Defects, Coll, Kiev 1972, 203–206 ( in Russian)

136. Electron-microscopical investigation of generation of radiation defects on irradiation of alkali halide crystals by electron beam and ultraviolet radiation: Kh R V Yygi, Uzv AN SSSR Ser Fiz, 36 (9), 1972, 1990–1993 ( in Russian)

136. Electron-microscopical investigation of generation of radiation defects on irradiation of alkali halide crystals by electron beam and ultraviolet radiation: Kh R V Yygi, Uzv AN SSSR Ser Fiz, 36 (9), 1972, 1990–1993 ( in Russian)