Formation of disperse particles under high-power ion beam irradiation of metals with a coating

Metal systems based on aluminum and copper coated with nickel irradiated by a high-power ion beam of nanosecond duration have been studied by scanning electron microscopy and local X-ray microanalysis. Dispersed particles of micro- and nanosizes have been found on the surface target. Their composition and formation mechanism differ. It has been shown that microparticles were formed during mixing of film and target atoms and consisted of corresponding components. Nanoparticles were mainly composed of the coating material, and their formation was associated with the dispersion of the Ni film due to the presence of a thin oxide layer on the sample surface. The deposition of Ni ablated by a high-power ion beam can affect the formation of nanoparticles.     

Charge transport and accumulation in dielectrics upon irradiation by an electron beam

The transient process of charge accumulation in a dielectric with exposed surface is considered for the case of irradiation by a beam of electrons with path lengths less than the specimen thickness. For the case of shallow traps the characteristic method is used to solve the problem of passage of the space charge density front through the specimen volume from a virtual cathode located at a depth equal to the path length of the primary beam electrons to a grounded electrode. Transient patterns of field intensity and space charge density over dielectric layer thickness are found. Special features of the transient process are considered, related to the fact that the charge carriers are being injected into the dielectric by an electron beam. Furthermore, an expression is obtained describing the kinetics of formation of the exposed dielectric surface potential, and the dependence of these kinetics on radiation parameters and dielectric properties are considered. The conclusions of the model are compared to experiment.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 20–25, August, 1988.     

带状束高功率微波源宽通带收集极

设计了一种适用于带状电子束高功率微波源的宽通带收集极,在有效吸收束-波相互作用后的带状电子束的同时,保证了带状电子束高功率微波源的工作模式矩形波导TM11模式高效率地通过。研究结果表明：在13~27 GHz范围内,功率传输效率大于95%,这一宽通带特性使得该类型的收集极与带状电子束高功率微波源能够更好配合,显著提高了微波源的模拟优化和实验调试效率;TM11模式微波的传输效率对收集极厚度和长度等参数不敏感;该类型收集极结构具有良好的散热能力,在不加外部水冷装置的条件下,仅靠空气自然对流冷却和辐射冷却,可以承受电流3 kA、电压300 kV、脉冲宽度30 ns及重复频率50 Hz带状电子束的连续冲击。     

Erosion of the GaAs target under irradiation by a high-power pulsed ion beam

The results of examination of the GaAs-target erosion under irradiation by a high-power pulsed ion beam are reported. In the experiments, use was made of a high-power pulsed ion source with the following parameters: ion energy — 250 keV, target current density — 350 A/cm², pulse duration — 80 ns, target energy density — up to 7 J/cm². The target erosion coefficient and its dependence on the number of successive pulses are measured. It is found that the surface roughness parameter is increased with the number of successive beam pulses. A regular structure of surface relief is observed to form in the case where the number of pulses > 20–40. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 66–70, January, 2007.     

Nanostructuring of the surface of aluminum alloys under irradiation by a high-power ion beam

The surface morphology of aluminum alloys under irradiation by a high-power nanosecond ion beam with a low current density is investigated. The possible factors responsible for the change in the surface relief are considered.     

Energy of a shock wave generated in different metals under irradiation by a high-power laser pulse

The energies of a shock wave generated in different metals under irradiation by a high-power laser beam were determined experimentally. The experiments were performed with the use of targets prepared from a number of metals, such as aluminum, copper, silver and lead (which belong to different periods of the periodic table) under irradiation by pulses of the first and third harmonics of the PALS iodine laser at a radiation intensity of approximately 10¹⁴ W/cm². It was found that, for heavy metals, like for light solid materials, the fraction of laser radiation energy converted into the energy of a shock wave under irradiation by a laser pulse of the third harmonic considerably (by a factor of 2–3) exceeds the fraction of laser radiation energy converted under irradiation by a laser pulse of the first harmonic. The influence of radiation processes on the efficiency of conversion of the laser energy into the energy of the shock wave was analyzed.     

Microstructure of metals and alloys in the heat-affected zone produced by a high-power ion beam

The microstructure of heat-affected zones produced by high-power ion beams in Al, Cu, Ni, and AD1 and Monel alloys are investigated by optical and scanning electron microscopy and X-ray diffraction analysis. It is ascertained that the microstructure is divided into characteristic layers differing in terms of grain sizes and phase components. It is shown that the formation of the structural-phase states of each layer occurs in both solid and liquid phases under pulsed ion-beam treatment and depends on the irradiation parameters and the thermophysical characteristics of a target.     

Visible photoluminescence from silicon nanopowders produced by silicon evaporation in a high-power electron beam

Silicon nanopowders produced by electron-beam-induced evaporation of a bulk silicon sample in an argon atmosphere are studied by the photoluminescence technique and Raman scattering spectroscopy. A photoluminescence peak in the visible region of the spectrum has been detected at room temperature in powders consisting of silicon nanocrystals. The strong short-wavelength shift of the photoluminescence peak can be attributed to the quantum size effect of electrons and holes in small silicon nanocrystals (about 2 nm). The size of silicon nanocrystals is determined by analyzing Raman spectra, and it is consistent with estimates obtained from photoluminescence data.     

Intensification of chemical reactions in aqueous solutions upon irradiation with an accelerated electron beam

The results from investigating the effect of radiation exposure on the rate of chemical reactions in acid aqueous solutions of Fe²⁺, which are widely used in hydrometallurgy of nonferrous metals to extract the target components into solution from ores, are presented. The potential of the applied method is demonstrated.     

Surface structure of alumina ceramics during irradiation by a pulsed electron beam

The structural transformations that occur in the near-surface layer in alumina ceramics during irradiation by a pulsed electron beam generated by a forevacuum plasma electron source are studied. The modification of the surface properties of the ceramics is shown to be caused by the formation of regions consisting of close-packed and identically oriented crystallites within every grain. The crystallites are elongated: their length and width are 0.5–1.5 μm and the transverse size is 0.1–0.2 μm.     

Evolution of the dislocation substructure in an annealed pro-eutectoid steel upon irradiation with a high-current electron beam

The gradient evolution of the dislocation substructures of an annealed pro-eutectoid steel whose surface was treated with a pulsed low-energy, high-current electron beam has been quantitatively analyzed with the use of transmission diffraction electron microscopy.     

“Instantaneous” spectrum of passively ionized electrons in a dielectric irradiated by a high-power electron beam

A technique is developed for theoretical analysis, and the “instantaneous energy spectrum,” that is, the energy spectrum of passively ionized electrons in a dielectric irradiated by an electron beam of moderate or high density which arises prior to electron-phonon relaxation is calculated. The source of the beam is usually a high-current electron accelerator. The computation algorithm is designed so as to make it possible to fully take into account and make use of the following data: first, the actual (measured) spectrum of the electron beam; second, the complete electron spectrum of the dielectric, including the spectrum of the density of occupied states, which is continuous within the valence bands and discrete in the region of the low-lying quasiatomic levels; and the spectrum of the density of unoccupied states, which begins in the conduction band and, in a continuous process, turns into the spectrum of quasi-free electrons in the crystal; third, the differential ionization cross-sections of the atoms due to electron impact, which the present report refines so as to take in into account the actual spectrum of the density of the final states; the latter spectrum is continuous within the valence bands and discrete in the region in which the law of dispersion of a band electron turns into the law of dispersion of a quasi-free electron. The results of the theoretical analysis are compared with the data of a numerical experiment carried out in the present report by the Monte-Carlo method using the same initial data. The agreement between the theoretical results and the data from the numerical experiment demonstrates the stability and reliability of the algorithm used to calculate the instantaneous spectrum. The precision of the calculation is determined solely by the initial data. The instantaneous spectrum which is obtained is the initial distribution function for all the kinetic equations describing subsequent relaxation of the electrons in the irradiated dielectric. Tomsk Polytechical Institute. Tomsk State University. Institute of High-Current Electronics, Russian Academy of Sciences (Siberian Division). Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 136–144, November, 1996.     

Internal structure transition of spin-on glass by electron beam irradiation

The effects of electron beam (EB) irradiation on spin-on glass (SOG) were investigated using thermal desorption spectroscopy. We were able to employ heat treatment as a “development process”, since we discovered that heat treatment breaks different bonds in SOG depending on whether it is applied before or after EB irradiation of SOG. In the case, when heat treatment was applied before EB irradiation of SOG, it was possible to break the Si-C bond at about 500 °C. In the case, when heat treatment was applied after EB irradiation of SOG, on the other hand, the -SiC bond could be broken at a lower temperature of about 400 °C. Using this difference between the two bond-breaking temperatures, it was possible to develop SOG using thermal desorption development (TDD). Moreover, the bond-breaking mechanisms revealed that the organic components in SOG play an important role in TDD. Hence, in order to determine the influence of organic components on TDD, the development characteristics of SOG samples with 10% and 15% organic contents were investigated.     

Surface chemical changes of CaTiO3:Pr upon electron beam irradiation

Surface chemical changes of CaTiO₃:Pr³⁺ phosphor material and their effect on the red emission intensity of the ¹D₂→³H₄ transition of Pr³⁺, upon electron beam irradiation are presented. Red emission at 613 nm was obtained upon probing the surface with a 2 keV electron beam. The surface chemical changes and Pr³⁺ red emission were monitored using an Auger Electron Spectroscopy (AES) and Cathodoluminescence (CL) spectrometer, respectively. The CL intensity decreased with a decrease in O on the surface at 1×10⁻⁸ Torr base pressure and decreased with an increase in O on the surface at 1×10⁻⁶ Torr O₂. The X-ray Photoelectron Spectroscopy (XPS) revealed that CL degradation at 1×10⁻⁶ Torr O₂ is due to the formation of CaO and CaO_x as well as TiO₂/Ti₂O₃ non-luminescent species on the surface.     

Phase motion of particles upon formation of subpicosecond electron bunches in a traveling wave under heavy beam loading

The possibility of efficient bunch compression due to the phase motion of particles in the field of a traveling wave is demonstrated. The calculated bunch length is 120 μm, which makes it possible to expect spontaneous coherent radiation from the undulator at a wavelength of 240 μm.     

Plasticization of face-centered metals under electron irradiation

The effect exerted by an electron beam with an energy of 0.5 MeV on the deformation of polycrystalline aluminum (99.5%) and copper (99.5%) under uniaxial tension at a rate of 2 × 10^?4 s^?1 in the temperature range from 40 to 100°C has been investigated. It has been established that the plasticity of the metal increases under irradiation with an electron beam: the level of the flow stress and the strain hardening coefficient in the irradiated state decrease, whereas the total resource of plasticity of the material increases. A mechanism of an increase in the plasticity of metals has been proposed. This mechanism is based on the radiation-induced generation of nonlinear strongly localized excitations of the crystal lattice, namely, discrete breathers, whose lifetime is significantly longer than the relaxation time of phonons. The interaction of discrete breathers with dislocations can stimulate the detachment of dislocations from stoppers and, consequently, an increase in the plasticity of the material.     

Characterization of structural modifications in poly-tetra-fluoroethylene induced by electron beam irradiation

The effects of electron beam irradiation doses on the poly-tetra-fluoroethylene (PTFE) have been studied. Several techniques, such as X-ray diffraction (XRD), differential scanning calorimetry (DSC), mechanical properties and Fourier transform infrared spectroscopy (FTIR) were applied to characterize the PTFE samples and to study the radiation effects on the crystal structure of the polymer.The irradiation dose up to 150 kGy showed an increase in the crystallinity degree of PTFE, which has been observed and confirmed during the DSC and XRD measurements. The increase in crystallinity was attributed to the scissions of the chain in the amorphous region. Moreover, the number-average molecular weights were estimated from the heat of crystallization measured by DSC technique. The results indicated that the molecular weights were decreased by increasing the heat of crystallization due to irradiation with doses up to 150 kGy. Radiation resistance of the irradiated and non-irradiated PTFE was investigated during its mechanical properties at room temperature. The dose at half value of the elongation at break is about 3.10 kGy while the dose at half value of the tensile strength is about 1.70 kGy.     

Evolution of the glow of an aerogel irradiated with a high-power pulse electron beam

The evolution of the glow of the energy-release zone in porous transparent aerogel, with a density of 0.03–0.25 g/cm³, which is irradiated by a high-power pulse electron beam, is studied experimentally. In addition to a fast (τ≤τ_beam) and a luminescent (τ≈10⁻⁶ s) glow components, a slow glow component (τ≈2×10⁻⁵ s) has been revealed. The appearance of this slow component is associated with an aerogel rarefaction wave and its destruction (cracking) arising after its isochoric bulk heating by electron radiation, which may occur due to an electrostatic field induced under irradiation. The discovered glow is utilized to visually determine the current position of the rarefaction wave front. The sound velocity measured as a function of the density of SiO₂ aerogels with porosities of 10–100 allowed us to experimentally determine the percolation parameter of the aerogel equation of state.