Investigation of the effect of nucleus charge and atomic electron distributions on the processes of polarized bremsstrahlung of electrons in crystals

The process of polarized bremsstrahlung of electrons in crystals has been theoretically investigated with application of the new method taking into account the screening of the Coulomb nucleus field by atomic electrons. Real changes in the cross sections of both polarized and unpolarized bremsstrahlung and the degrees of particle polarization in a silicon crystal are obtained.     

Weak and magnetic inelastic scattering of antineutrinos on atomic electrons

Neutrino scattering on electrons is considered as a tool for laboratory searches for the neutrino magnetic moment. Inelastic $\bar \nu _e e^ - $ scattering on electrons bound in the germanium (Z=32) and iodine (Z=53) atoms is studied for antineutrinos generated in a nuclear reactor core and in ⁹⁰Sr-⁹⁰Y and ¹⁴⁷Pm artificial sources. On the basis of the relativistic Hartree-Fock-Dirac model, both the magnetic-and weak-scattering cross sections are calculated for the recoil electron energy range between 1 and 100 keV, where a higher sensitivity to the neutrino magnetic moment could be achieved. Particular attention is paid to an approximate procedure that allows us to take into account the effects of atomic binding on the inelastic-scattering spectra in a simple way.     

Analysis of inelastic scattering processes of electrons by localized electrons in quantum dots

The inelastic Coulomb scattering rate 1/τ_in of conduction electrons has been theoretically evaluated in the presence of localized states such as quantum dots. By a diagrammatical method, we have formulated 1/τ_in and its relation to the conductivity σ_loc(ω) through localized states. The dependence of τ_in on temperature T is examined in the case that σ_loc(ω) follows the Mott's model. It is found that 1/τ_in varies as T²(ln Δ/T)^d+1 where d is the dimensionality and Δ is tunneling energy between the localized states in the asymptonic T = 0 limit, in agreement with Imry's calculation. It is also found that calculated 1/τ_in deviates from T²(ln Δ/T)^d+1 as T increases, suggesting the importance of correction term at high temperature.     

Total negative refraction in real crystals for ballistic electrons and light

It is found that there exists a category of material interfaces, readily available, that not only can provide total refraction (i.e., zero reflection) but can also give rise to amphoteric refraction (i.e., both positive and negative refraction) for electromagnetic waves in any frequency domain as well as for ballistic electron waves. These two unusual phenomena are demonstrated experimentally for the propagation of light through such an interface.     

Importance of electron-phonon processes in the inelastic lifetime of conduction electrons

The temperature of conduction electrons can be raised above the lattice temperature by a high electric current density. The achieved temperature difference is proportional to the electron-phonon relaxation time. Weak localization yields information about the electron temperature and allows the conclusion that electron-phonon processes are an essential determinant for the inelastic lifetime of the conduction electrons.     

Energy load of a gyrotron collector with allowance for electrons reflected from its surface

We develop a physical model and an algorithm for calculation of the specific density of power scattered by a collector in high-power gyrotrons with allowance for multiple reflections of electrons from the collector surface. Specific features of the angular and energy distributions of reflected electrons in the case of their oblique incidence on the collector surface are taken into account. Electron trajectories and the corresponding power-density distributions for typical collector systems of the gyrotrons are found. Multiple reflections of electrons significantly increase the effective collector surface and reduce the thermal load. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 52, No. 1, pp. 55–62, January 2009.     

Monte-Carlo study of electromagnetic showers of high energy electrons and photons in aligned crystals

Abstract

A Monte–Carlo program to investigate electromagnetic shower formation in single crystals for particle energies up to 300 GeV is presented. It is based on the well known EGS4-code for amorphous materials and accounts for coherent radiation and pair production which arise in a crystal. Channeling radiation and crystal field assisted pair production are calculated within the uniform field approximation. The increase of energy loss of channeled electrons due to radiation cooling is also included. Good agreement with the available experimental data can be reported.     

Cherenkov instability of a magnetized beam-plasma system with allowance for a momentum spread of beam electrons

Cherenkov instability is considered in a completely magnetized homogeneous beam-plasma system featuring a thermal momentum spread of beam electrons. The thermal spread in the beam is described in the scope of both the hydrodynamic approach and the kinetic equation method by giving the electron momentum distribution function in the form of theMaxwellian and semi-Maxwellian distributions. It is shown that two beam-plasma instability regimes, the single-particle and collective Cherenkov effects (Compton and Raman regimes) differing by the physical mechanism and the increments, are possible in a system (waveguide) with homogeneous transverse beam and plasma density profiles. Solutions to dispersion equations for these and a more general regime are obtained and analyzed.     

Parametric channeling and collapse of beams of charged particles with internal structure in crystals: 2. Parametric processes during channeling of atomic ions, nuclei, and relativistic electrons in crystals

Features of parametric effects during channeling of atomic ions, nuclei, and relativistic electrons (positrons) in crystals were considered. It was shown that parametric coupling between ion channeling states in the field of crystal axes and planes and electronic states in the ion volume leads to the possibility of “parametric collapse” of the beam, i.e., a decrease in the oscillation amplitude of the atomic ion in the channel due to periodic transfer of the ion oscillation energy to the inner electron of the atom. The same effect can be used to cool beams due to energy transfer to intrinsic nuclear states with low energy levels. It was shown that parametric cooling of beams with a decrease in the transverse energy can also occur during axial channeling of relativistic electron beams. This process results from the parametric coupling between channeling states, which are caused by the particle charge and electron spin states in an effective magnetic field induced in the moving coordinate system.     

Bremsstrahlung of nonrelativistic electrons in metals with allowance made for the polarization channel

We theoretically investigate the bremsstrahlung that appears when nonrelativistic electrons are scattered in a metal target with allowance made for the polarization contribution. We take into account the interference of ordinary and polarization bremsstrahlung, the absorption of radiation in the target material, the energy losses and elastic scattering of an electron by atoms of the medium, and the coherent effects when the radiating electron interacts with the target. We analyze the influence of the target thickness on the process and the contribution of polarization bremsstrahlung to the total yield of bremsstrahlung photons as a function of the problem parameters.     

Permittivity of complex oxide crystals with allowance for spatial dispersion

The temporal and spatial dispersions of the permittivity of complex oxide crystals, which have numerous branches of dipole active oscillations, is considered. Formulas for calculating the susceptibility spectra of complex oxides in the terahertz region with allowance for both types of dispersion are obtained in the resonance approximation of photon-phonon interaction using quantum Green’s functions. The calculation results are used to discuss the well-known experimental data.     

Radial-velocity distribution of electrons in an axially symmetric focusing electromagnetic field

We construct the distribution function of beams of charged particles with assigned angular momentum in an axially symmetric electromagnetic field. We find a distribution function that enables us to establish a connection between the effective size of the beam and its parameters.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 87–91, September, 1985.     

Ordering kinetics in bcc alloys with allowance for diffusion processes

The kinetics of inhomogeneous ordering in binary bcc substitution alloys of arbitrary stoichiometry is considered with the account for for diffusion processes. A system of kinetic equations describing the joint evolution of the occupancies of two sublattices of a bcc lattice is derived using a phenomenological approach. It is shown that, even within the mean-field approximation, this approach allows one to describe simultaneously the processes of establishment of the long-range order and diffusion of the alloy components. Numerical analysis of the obtained system of equations showed that quick onset of long-range order first occurs, which is followed by slow diffusion of the alloy components.     

Elastic scattering of electrons on nuclei with allowance for the second born approximation

In the framework of the shell model of light nuclei, the contribution to the scattering cross section of the second Born approximation due to the interference between the electric Coulomb interaction and the magnetic-dipole interaction is calculated. The case of backward scattering is considered. For not too high energies of the incident electrons, convenient approximate expressions are obtained for the correction to the cross section.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 12–15, January, 1981.