Multiplication of high-energy electrons in irradiated materials studied using the Boltzmann kinetic equation

Processes involved in the formation of electron collision cascades created by nonrelativistic high-energy electrons, which can develop in materials exposed to electron and gamma radiation fluxes, have been considered. The problem is solved using the Boltzmann kinetic equation for high-energy electrons moving in a medium. A model scattering indicatrix is constructed for this equation with an arbitrary potential of interaction between colliding particles. Using this scattering indicatrix, the distribution of the particle energies is obtained. Based on this energy distribution (with an arbitrary interparticle interaction potential), a cascade function is found that describes the multiplication of knock-out electrons (electron cascade) generated when a high-energy electron with a certain energy is scattered on the electron subsystem of the irradiated material. The cascade function has been calculated for the Coulomb potential of the interaction between a high-energy electron and atomic-shell electrons.     

Sputtering of solids by heavy ions and temperature effects in electronic and lattice subsystems

The results of sputtering coefficient measurements for pure metals, alloys, amorphous alloys, semiconductors, and highly oriented pyrolytic graphite under irradiation by high energy ions are considered. The possible mechanisms of strong sputtering of materials with high defect concentrations are discussed. The three-dimensional thermal spike model (“hot ion track”) with the temperature dependence of thermodynamic parameters (specific heat thermal conductivity) is formulated for single-layer mono-and polycrystals and multilayer systems (materials). The results of a numerical solution to the introduced system of partial differential equations are considered for the lattice and electronic subsystem temperatures around and along the fast heavy ion trajectory as a function of the time t, as well as radial r and longitudinal z coordinates, taking into account possible phase transitions such as melting and evaporation. The results obtained are discussed.     

Numerical study of the thermal processes occurring in materials under irradiation with high-energy heavy ions

Numerical simulation of the thermal processes occurring in indium phosphide under the action of a heavy gold ion with the energy E ₀ = 200 MeV is carried out. The problem is solved taking into account phase transitions of the melting and evaporation types. Numerical studies are carried out on the basis of a modified thermal-peak model and the obtained results are analyzed.     

Investigation of thermal processes in single crystals irradiated with high-energy heavy ions

The thermal processes arising in InP and GaAs single crystals irradiated with high-energy heavy ions are investigated with the help of a thermal peak model. Numerical simulation is used to estimate the sizes of regions where the melting process can occur and the structural changes arising in the irradiated materials are observed.     

Influence of temperature and electrolyte ions on the properties and spectrum of solvated electrons in irradiated hexamethylphosphortriamide

Abstract

Radiation-induced latchup in commercially available junction-isolated integrated microcircuits is reported. Four different types of construction of integrated microcircuits have been examined. They include quadruplediffused, diffused collector, epitaxial, and epitaxial with buried layer (gold-doped). It was found that pnpn switching could be obtained between isolated components on these devices. In fact, pnpn paths were quite common in all but the last type mentioned. The current gains of the parasitic transistors involved in these pnpn paths were measured and were, in most cases, shown to indicate that pnpn switching should occur. However, important exceptions were seen. Latchup between these isolated components could be induced by a pulse of ionizing radiation even with a reverse bias on the substrate of the microcircuits. As a result of this investigation, it is concluded that the pnpn mechanism, since it is so common, is a majorcause of latchup in junction-isolated integrated microcircuits.     

Use of the temperature peak model for the description of track formation in semiconductor crystals irradiated by fast heavy ions

An attempt to apply the temperature peak model to describe the formation of defects and tracks in semiconductor crystals is made for the first time. The temperature dependences of model parameters, such as specific heat, thermal conductivity, and electron-phonon coupling coefficient are obtained. Agreement between the theoretical results and experimental data for InP and Ge crystals irradiated by ultrafast heavy ions indicates the adequacy of the model, with which one can evaluate the temperature of the local area near the ion trajectory, as well as the diameters of the molten region and experimentally observed track region. The diameter of the cylindrical molten region that forms along the path of 250-MeV Xe⁺ ions in InP is predicted to be 20 nm, and the measured cross-sectional diameters of the tracks fall into the range 7–15 nm.     

Unusual band structure and exotic electrical conduction for electrons in incommensurate lattice potentials

Electrons in crystals with incommensurate periodic potentials are shown to exhibit a band structure with many very narrow bands separated by narrow band gaps. This makes such systems ideal candidates for observing such exotic electrical conduction phenomena in d.c. fields as Zener tunneling and Stark oscillations. Estimates are made of the conditions under which such phenomena should be observable experimentally.     

On a generalization of the Gibbs equation for heat conduction

A generalized Gibbs equation for the heat conduction problem is proposed in order to take finite wave speed into account.     

Conductivity of irradiated Kapton in relation to energy loss of ions and electrons

Abstract

We have studied the effects of 2.5 MeV electron irradiation and ion (C, N, F, Si and Kr) bombardment on the electrical conductivity of a polyimide (Kapton-H) with ion energies ranging between 320 keV (N) and 1.25 GeV (Kr). In this wide range of situations we have tried to sort out the respective effects of nuclear and electronic excitation energy losses.

For all ion irradiation the conductivity is found to scale with the electronic excitation absorbed dose: i.e. a power law of conductivity versus absorbed dose with an exponent around 9 is observed. At a given absorbed dose (in Gray units) the efficiency of each ion to enhance conductivity is found to be proportional to the electronic energy loss; electrons are much less efficient than ions and thus collective excitations are required to achieve this process.

The nuclear energy loss can perhaps play some role at conductivities higher than 100 Ω^?1 m^?1, but its effects are negligible in the range explored here.     

Phenomenological model of the accumulation of a space charge by high-energy injection of electrons in high-resistivity materials

The assumption of a constant ratio of the density of free carriers to the total carrier density in the process of electron injection is used to develop a phenomenological model of the accumulation of a space charge by high-energy injection. Use is made of the concept of a quasi-Fermi level in the case of an exponential distribution of trap energies.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 96–98, May, 1980.     

塑料闪烁光纤在高能中子辐照下质子分布特性的数值模拟

 利用Geant4系统模拟了在高能中子照射下,塑料闪烁光纤中产生的反冲质子的分布特性,分析了入射中子能量分别为2,4,6,8 MeV时,产生的反冲质子能量和方向分布,给出了反冲质子在不同方向上的能量分布。结果表明:向前和向后出射的质子分布不对称;反冲质子的能量在零与入射中子能量之间连续地分布;接近垂直入射方向产生的质子数较多;入射中子能量越高,产生质子数越少;反冲质子的出射角度越小,其能量越大,即沿着入射中子方向的反冲质子能量较大,垂直入射方向的反冲质子能量较小。     

The stationary state and the heat equation for a variant of Davies' model of heat conduction

We study a variant of Davies' model of heat conduction, consisting of a chain of (classical or quantum) harmonic oscillators, whose ends are coupled to thermal reservoirs at different temperatures, and where neighboring oscillators interact via intermediate reservoirs. In the weak coupling limit, we show that a unique stationary state exists, and that a discretized heat equation holds. We give an explicit expression of the stationary state in the case of two classical oscillators. The heat equation is obtained in the hydrodynamic limit, and it is proved that it completely describes the macroscopic behavior of the model.     

Spectroscopic investigation on the lattice dynamics of different cut quartz samples irradiated by neutrons

A spectroscopic study of the effect of neutron radiation on the lattice dynamics of different cut crystalline and glassy quartz (SiO₂) has been performed. The IR spectroscopy method is used to determine the mechanisms by which the spectral characteristics of deformation and valence vibrations vary by radiation-induced alteration of the lattices in two types of modified quartz (α-SiO₂ and ν-SiO₂) as a function of the neutron fluence at low and high frequencies. It has been established that nonlinear changes in the dose dependences between the spectral characteristics of the fundamental modes occur in two types of crystals, with different orientations, and in glass, and the features of the spectrum modifications exist near 300–550 and 700–1400 cm⁻¹ and at higher frequencies. The derived dose dependences are compared to those of the degenerate vibration parameters in ν-SiO₂, and the extreme kinetics of the force coefficients is determined. A conclusion is made that the accumulation of radiation damages, changes in the force field around the bridge bonds, and the phase states of SiO₂ affect the observed specific behavior of the radiation-modified spectral and force parameters of the degenerate and deformation modes in quartz samples of different types.     

Graft polymerization into the latent tracks of some perfluoropolymers films irradiated by heavy ions

The results of the graft polymerization of methacrylic acid into perfluoropolymers (the copolymer of tetrafluoroethylene with hexafluoropropylene, copolymer of tetrafluoroethylene with perfluoroallylether) irradiated with heavy ions (Kr, 430 MeV) are presented. It has been found that the graft polymer quantity depends upon the polymer nature and the ion fluence. The graft polymer amount and its penetration depth were measured by the weighting methods, the dye sorption and electron microscopy methods. The graft polymerization results in significant changes in the polymer volume and structure.     

Nanoisland nucleation in thermal spike regions on the material surface irradiated by swift heavy ions

The energy that is lost by swift heavy ions (SHIs) in a material highly excites its electronic subsystem, while the ion subsystem initially remains almost unperturbed. Subsequent energy transfer from the excited electrons to target atoms may cause a short-term local temperature rise (thermal spike), which, in turn, may induce phase transitions in the nanodimensional region near the ion trajectory. The possibility of nanoisland nucleation within such spikes on the material surface exposed to SHIs is studied. Presumably, the nanoislands appear when the characteristic nucleation time is shorter than the time of spike region cooling. It is shown that the maximal nucleation rate may be observed at a distance of the center of the spike. This may result in the annular distribution of the islands around the SHI trajectory.     

Electrical and optical properties and stabilization of the Fermi level in GaP crystals irradiated by electrons and H+ ions

Electrical and optical properties and Fermi level stabilization are studied in GaP crystals irradiated by electrons (E2.2 MeV, D1·10¹⁹ cm^–2) and H⁺ ions (E5 MeV, D1.7·10¹⁶ cm^–2). It is shown that the limiting position of the Fermi level (F_limE_G/2±0.2 eV) is independent of the initial GaP parameters and the type of bombarding particle, but is determined by the condition of local neutrality of the defective GaP. Resistivity values for the irradiated specimens of _max(D)1·10¹³ ·cm were obtained at 300 K. At maximum integral particle fluxes a decrease in crystal resistivity to (3–6)·10⁹ ·cm was observed. The readjustment of GaP absorption spectra in the region hvE_G upon irradiation is related to recharging of gap states by radiation defects upon motion of the Fermi level toward F_lim.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 37–42, December, 1994.