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编号 9 (2024)
Articles
Ultracold neutron source based on superfluid helium for the PIK Reactor
摘要
A high density ultracold neutron source based on superfluid helium is going to be created in NRC “Kurchatov Institute” — PNPI for scientific research in fundamental physics. The ultracold neutron source is to be installed on the Horizontal Experimental Channel 4 (HEC-4), which is the biggest of available experimental channels of PIK Reactor Complex. Thermal neutron flux density at the channel outlet is expected to be around 3 × 1010 cm–2s–1. The new ultracold neutron source at the PIK Reactor is planned to achieve a density of 2.2 × 103 cm–3 at ultracold neutron neutron guide exit and 200 cm–3 at neutron electric dipole moment spectrometer facility. The designed ultracold neutron guide system is going to support five experimental facilities alternately. At the initial stage the ultracold neutron source is planned to be equipped with already existing PNPI experimental plants: a neutron electric dipole moment spectrometer and neutron lifetime measuring facilities (with a gravitational and magnetic trap). A unique technological cryogenic complex with superfluid helium was designed and realized for this ultracold neutron source. Said complex includes equipment for achieving temperatures down to 1 K and removal of up to 60 W of heat from superfluid helium.
3-11
Estimation of the coherently scattering domain size in alloys from neutron diffraction data
摘要
An analysis of the diffraction spectra of the Fe74Al26 alloy was conducted using a high-resolution neutron diffractometer to determine the size distribution of structurally ordered clusters dispersed within the structurally disordered matrix of the alloy. The Scherrer method was generalized for this purpose, based on the analysis of diffraction peak profiles, determining peak widths at heights of 1/5 and 4/5 of the maximum, and assuming the validity of the gamma distribution for cluster sizes (Pielaszek method). A comparison of results obtained using the Scherrer, Williamson–Hall, and Pielaszek methods was carried out, demonstrating good agreement between them. An algorithm for calculating the log-normal distribution function of cluster/particle sizes is proposed. The experimental data were obtained using a time-of-flight neutron diffractometer, and the analysis was performed for two variants of variable scanning: in crystallographic (direct) (d-scale) and reciprocal (H-scale) spaces, with estimates of possible systematic errors. It was concluded that the determined average sizes possess the necessary degree of stability, meaning they weakly depend on the applied variable scanning and the total number of experimental data points.
12-24
Influence of vacuum ultraviolet on changes in Fourier-transform infrared spectra, electrical and hydrophobic properties of a composite based on polyimide track membranes filled with silica
摘要
Vacuum ultraviolet radiation is a part of ultraviolet radiation with a very short wavelength and is a component of cosmic radiation. Composite materials based on polyimide have great potential for protection against cosmic radiation. The paper presents the results of studies on the effect of vacuum ultraviolet radiation on a polyimide film, a polyimide track membrane and a composite material based on a polyimide track membrane filled with silicon dioxide nanofibers. Mass losses, dielectric properties, Fourier-transform infrared spectra and wettability of the studied samples before and after vacuum ultraviolet irradiation were studied. It was found that the lowest mass losses during vacuum ultraviolet irradiation are observed in a composite material based on a polyimide track membrane filled with SiO2; the dielectric constant of the composite film after vacuum ultraviolet irradiation increased by 65.8%. It was established that the effect of vacuum ultraviolet irradiation on the films under study is accompanied by the destruction of a small amount of the following bonds: C=O, C–O, C–C and C–N. At the same time, vacuum ultraviolet caused the least damage to the developed composite material. Analysis of the contact angle of the studied samples showed that the surface of the polyimide film, polyimide track membrane, composite material remained hydrophilic. No changes were detected in the structure of the film surface.
25-34
Synthesis of gallium (II) sulfide
摘要
The synthesis of gallium (II) sulfide was carried out from elements in a closed volume using a two-temperature method. Passivation of the gallium surface in vacuum is observed up to temperature of 1623 К. The controlled chemical reaction was carried out in a hydrogen atmosphere at a pressure of 1300–2600 Pa. Similar results were achieved in vacuum using photocatalysis with ultraviolet radiation at a wavelength of 240–320 nm with a radiant power of 24.6 W. In both cases, at the temperature of 1323–1373 К, the gallium (II) sulfide synthesis time took no more than 30 minutes with a loading mass of 100 g. The Rietveld method was used to characterize crystalline gallium (II) sulfide by powder X-ray diffraction. The results of analysis showed that the product of the chemical reaction is single-phase GaS. The proposed solution to the problem of the gallium melt surface passivation for sulfur oligomers from the point of view of quantum electrodynamics made it possible to significantly reduce energy costs and increase the synthesis efficiency of extra pure gallium (II) sulfide for its further use in the chalcogenide glasses production.
35-41
Experimental and numerical study of damage caused by high-current electron beam of construction materials intended for the first wall of powerful plasma installations
摘要
An experimental study of the effect of high-current electron beams on crystals made of polycrystalline tungsten and corrosion-resistant ferritic-martensitic steel EK-181 was carried out, as well as a numerical simulation of the process of interaction of the beam with the target, in which the energy of the electron beam is absorbed in the near-surface layers of the samples under study. The experiments are carried out on the Kalmar high-current electron accelerator at an average pulse energy of E ≈ 100 ± 20 J (pulse duration at half maximum 100 ns). During the experiments, samples were irradiated from one to ten times. In the numerical modeling, electron spectra were used, calculated on the basis of data (currents and voltages in the diode gap) obtained as a result of electrical measurements. The difference in the nature of destruction of tungsten and steel was demonstrated. It has been shown that tungsten begins to crack after three-pulse exposure with an energy of about 100 J, which correlates well with tests on other types of installations. On steel, minor cracking was observed only after 8–10 pulses of exposure. Numerous traces of droplets of melting and redeposition of the target material were found on the surface of the steel target. For both materials, the specific amount of energy that is absorbed in the region of interaction of the electron beam with the target is estimated.
42-49
Estimation of internal charging potential of dielectrics coated with conductive film
摘要
The charging potentials of quartz glass coated with a conductive metallic film was evaluated. Estimations were made based on the measured dependence of the intensity of the cathodoluminescent signal on the energy of the incident electron beam. Calculations have shown that when quartz glass coated with a 14 nm thick Au film is irradiated, the charging potential can reach 1.7 kV at an electron energy of 10 keV and 2.7 kV at 15 keV. An estimation of the electric field generating under the surface of the grounded film has shown that the field strength does not exceed 4 × 107 V/cm.
50-57
Dependence of the silicon carbide radiation resistance on the irradiation temperature
摘要
The effect of high-temperature electron and proton irradiation on the characteristics of devices based on SiC has been studied. For the study, industrial 4H-SiC integrated Schottky diodes with an n-type base with a blocking voltage of 600, 1200 and 1700 V manufactured by CREE were used. Irradiation was carried out by electrons with an energy of 0.9 MeV and protons with an energy of 15 MeV. It was found that the radiation resistance of SiC Schottky diodes under high-temperature irradiation significantly exceeds the resistance of diodes under irradiation at room temperature. It is shown that this effect arises due to the annealing of compensating radiation defects under high-temperature irradiation. It is shown that this effect arises due to the annealing of compensating radiation defects under high-temperature irradiation. The parameters of radiation defects were determined by the method of non-stationary capacitance spectroscopy. Under high-temperature (“hot”) irradiation, the spectrum of radiation-induced defects introduced into SiC differed significantly from the spectrum of defects introduced at room temperature. The radiation resistance of silicon and silicon carbide is compared. The relatively small difference in the rate of removal of carriers in SiC and Si upon irradiation at room temperature is due to the fact that in SiC, in contrast to Si, there is practically no annealing of primary radiation defects during irradiation.
58-63
Synthesis of hydride phases based on TiZrNbMoTa high-entropy alloy
摘要
A high-entropy TiZrNbMoTa alloy with a body-centered cubic lattice has been synthesized. The interaction of the alloy with hydrogen is accompanied by the formation of samples containing hydride phases with tetragonal and cubic lattice. Hydrogen desorption from the hydride at high temperature leads to the formation of fine metal powder of the original alloy with a cubic lattice. Samples of the alloy and hydride phases were analyzed by X-ray diffraction and electron microscopy.
73-79
Features of the formation of layers on the surface of valve metals in the process of ion beam assisted deposition of metals from vacuum arc discharge plasma
摘要
Layers on the surface of aluminum, aluminum alloy, titanium and tantalum was formed by ion beam assisted deposition of metals. Formation of layers in ion beam assisted deposition mode, by means of the deposition of metal and mixing of precipitating layer with the substrate by accelerated (U = 20 kV) ions of the same metal from metal vapor and ionized plasma of vacuum (~10– 2 Pa) pulsed electric arc discharge, was carried out. Multicomponent amorphous layers containing atoms of the deposited metal, components of the substrate material, including oxygen of the surface oxide film, as well as hydrocarbon molecules as impurities were obtained. It is established that during ion beam assisted deposition of metals with getter properties (Zr, Cr, Er, Dy, etc.) on the surface of the studied materials, significant amounts of gases are captured from the residual atmosphere of the vacuum working chamber and are included in the composition of the formed layer. At the same time, the content of atoms of the substrate material in the layer is small. With ion beam assisted deposition of metals that do not exhibit getter properties, the content of impurities in the resulting layers is significantly less, their composition contains atoms of the deposited metal and the substrate material.
64-72
Structure, stacking faults and electrochemical behavior of α-Ta prepared by chemical vapor deposition
摘要
Using X-ray diffraction, scanning electron microscopy, glow discharge emission spectroscopy, electrochemistry and strength assessment, stacking faults in tantalum deposited in a helium environment on a copper substrate by chemical vapor deposition and their effect on the protective properties have been studied. It is shown that the probability of formation of stacking faults in deposited bcc tantalum in the {112} planes is a sensitive parameter with respect to the deposition conditions (temperature and helium content). With an increase in helium concentration from high to medium values, the sum of the probabilities of the formation of deformation (α) and twinning (β) stacking faults 1.5α + β in α-Ta increases five times (from 0.025 to 0.13%), with a decrease in temperature from 800 to 750°C — 35 times (from 0.025 to 0.89%). A decrease in the probability of formation of stacking defects in deposited α-Ta tantalum is associated with a significant increase in corrosion resistance and adhesion strength of the coating to the substrate. A mechanism for the formation of metastable hcp phases of tantalum on stacking faults in α-Ta in the {112} planes is proposed.
80-89
Determination of the ratio of atoms and molecules in a tellurium beam using a mass spectrometer
摘要
The work is devoted to clarifying the ratio of atoms and molecules of tellurium vapor in interaction with various metal substrates (copper, nickel, atoms (Te) and molecules (Te2) present in the tellurium vapor phase, in mass spectrometric measurements correspond to ion currents of monomers J(Te+) and dimers — J(Te2+). The work was performed on a molecular beam epitaxy unit with desorption flow control by mass spectrometry and surface condition by fast electron diffraction. A molecular tellurium beam was obtained using a Knudsen type source. In this work, it is shown that the proportion of monomers in the total desorption beam significantly depends on the temperature of the substrate. This dependence corresponds to the dissociation energy of Te2 molecules of the order of 1.18 eV. At high temperatures (900 K), the proportion of Te monomers can reach 85%, and at low temperatures (650 K) — 8%. This circumstance should be taken into account when the composition of the vapor phase from the beam source can affect the processes under study. In particular, in mass spectrometric studies of the interaction of the vapor phase with the surface of a solid, for example, in the process of molecular beam epitaxy of CdTe.
90-94
On anomalous diffusion of fast electrons through the silicon crystal
摘要
Anomalous diffusion is a random process in which the root-mean-square displacement of a particle from the starting point depends nonlinearly on time. The possibility of such behavior for high energy particles moving through the crystal under conditions close to axial channeling was found earlier. In this case, the rapid displacement of particles in a plane transverse to atomic strings (Lévi flights) is due to the temporary capture of the particles in planar channels. In this work, by means of numerical simulation, the anomalous diffusion exponent was found for different values of the energy of electron transverse motion in the (100) plane of a silicon crystal. It has been established that in the case of electrons with an energy exceeding by 1 eV the height of the saddle point of the potential of a system of atomic chains [100], the results are consistent with those obtained earlier. It has been confirmed that the anomalous nature of diffusion is due to the possibility of short-term capture of particles in planar channels. With increasing transverse energy, this possibility disappears, and diffusion becomes normal (Brownian).
95-100
Evaluation of the component composition and thickness of the modified layer of tungsten and tantalum carbides during stationary sputtering by helium ions bombardment
摘要
A method is proposed for calculating the component composition and thickness of a layer of two-component targets changed as a result of prolonged (stoichiometric) sputtering when irradiated with light ions. The method is based on a previously tested model of sputtering inhomogeneous two-component materials with light ions. In the case of stationary sputtering of tungsten and tantalum carbides with helium ions, the results of calculations of the component composition and thickness of the modified layer are presented in comparison with experimental data.
101-105
Microstructure and deformation behavior of novel metal–ceramic laminated composites Ta/Ti3Al(Si)C2–TiC
摘要
New metal–ceramic laminated composites Ta/Ti3Al(Si)C2–TiC were obtained by spark plasma sintering. The samples were synthesized at a temperature of 1250°C and a pressure of 50 MPa for 5 min. For the formation of composites, preceramic paper with a powder filler based on the MAX phase Ti3Al(Si)C2, as well as and metal foils made of tantalum, were used. The phase composition, microstructure and elemental composition were analyzed by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy, respectively. It was found that as a result of sintering, dense multilayer composites were formed, consisting of tantalum metal layers, ceramic layers containing Ti3Al(Si)C2, TiC and Al2O3 phases, as well as reaction layers ~13 μm thick at the metal–ceramic interface, enriched with Ta, Al and Si. Based on mechanical test data, the ultimate bending strength of the obtained composites was determined (σbs = ~430 MPa). Metal–ceramic laminated composites with a refractory tantalum layer were shown to exhibit a ductile fracture mechanism, accompanied by a more than fourfold increase in absolute deformation compared to a Ti3Al(Si)C2-based ceramic composite. This is achieved due to deflection, branching of cracks at the metal–ceramic interface and plastic deformation of tantalum layers.
106-112