Andrey V. Korol

Total bremsstrahlung spectra of 1 - 25 keV electrons on Ne and Ar

Bremsstrahlung (BrS) spectra formed in the collision of 1 - 25 keV electrons with Ne and Ar atoms are calculated for the photon energies in the range from 10 eV up to the tip end. We demonstrate the important role of the polarizational BrS mechanism in the formation of the total BrS spectrum over the whole region of photon frequencies.

A relativistic description of the polarization mechanism of elastic bremsstrahlung

A completely relativistic mechanism for describing polarization bremsstrahlung caused by an elastic collision of a charged particle with a many-electron target was suggested. Multipole expansions for the amplitude and cross section of the process taking into account radiation lag effects were obtained. Including higher order multipoles was shown to result in substantial asymmetry of the angular distribution of emitted photons compared with the dipole case and in a noticeable change in the spectral characteristics of polarization radiation. The cross section of polarization bremsstrahlung was found to increase logarithmically as the energy of incident particles grew.

The role of the polarization mechanism for emission of radiation by atoms over a broad photon frequency range

This paper develops an effective method for calculating the bremsstrahlung cross section with allowance for the polarization mechanism. We calculate the cross section of bremsstrahlung produced in the scattering of electrons and positrons by H and Kr atoms. We also demonstrate the important role of polarization bremsstrahlung in the formation of the total emission spectrum over the entire frequency range.

SCALING BEHAVIOUR FOR THE INNER-SHELL POLARIZATIONAL BREMSSTRAHLUNG CROSS SECTION

A simple method for the calculation of the polarizational bremsstrahlung (BrS) cross sections relying on the use of the Coulomb Green function is developed. This method is applicable to the description of photon emission in collisions of charged particles with non-relativistic atoms in the range of photon frequencies comparable to or above the ionization potentials of the inner atomic shells. We have established the scaling law for the generalized polarizability of an atom and investigated the scaling behaviour of the polarizational bremsstrahlung cross sections. Using our method, we have calculated the polarizational BrS cross sections for collisions of a proton with the Ne, Na, P and Ar atoms and compared them with those obtained in the Hartree-Fock approximation. Both approaches show good agreement.

Reconciling simulated melting and ground-state properties of metals with a modified embedded-atom method potential

We propose a modification of the embedded-atom method-type potential aiming at reconciling simulated melting and ground-state properties of metals by means of classical molecular dynamics. Considering titanium, magnesium, gold, and platinum as case studies, we demonstrate that simulations performed with the modified force field yield quantitatively correctly both the melting temperature of the metals and their ground-state properties. It is shown that the accounting for the long-range interatomic interactions noticeably affects the melting point assessment. The introduced modification weakens the interaction at interatomic distances exceeding the equilibrium one by a characteristic vibration amplitude defined by the Lindemann criterion, thus allowing for the correct simulation of melting, while keeping its behavior in the vicinity of the ground state minimum. The modification of the many-body potential has a general nature and can be applicable to metals with different characteristics of the electron structure as well as for many different molecular and solid state systems experiencing phase transitions.

Number of photons and brilliance of the radiation from a crystalline undulator

The scheme for accurate quantitative treatment of the radiation from a crystalline undulator in presence of the dechanneling and the photon attenuation is presented. The number of emitted photons and the brilliance of electromagnetic radiation generated by ultra-relativistic positrons channeling in a crystalline undulator are calculated for various crystals, positron energies and different bending parameters. It is demonstrated that with the use of high-energy positron beams available at present in modern colliders it is possible to generate the crystalline undulator radiation with energies from hundreds of keV up to tens of MeV region. The brilliance of the undulator radiation within this energy range is comparable to that of conventional light sources of the third generation but for much lower photon energies.

PBrS from Atomic Clusters and Fullerenes

This chapter is devoted to the description of the PBrS process in in collisions involving atomic clusters.

PBrS in Non-Relativistic Collisions of Structural Particles with Atoms and Ions

The qualitative picture of the PBrS process in a collision of two structural atomic particles is as follows. The colliding particles become mutually polarized and, thus, acquire induced dipole moments.

Stimulated Emission from CU

The possibility to generate a stimulated emission of the FEL type by means of a crystalline undulator is discussed. The considered range of photon energies, \(10^2\)–\(10^3\) keV, is inaccessible in conventional FELs. Three different schemes of achieving the lasing effect are presented: (a) a gamma-amplifier based on the use of a single CU; (b) a gamma-klystron which utilizes the sequence of two (or more) CUs; (c) a Crystalline Undulator Laser. We demonstrate, that despite a number of parasitic effects, present technologies are nearly sufficient to achieve the conditions needed to achieve the emission stimulation by means of CU. It is shown, that the brilliance of CUL radiation can be as high as \(10^{28}\)–\(10^{32}\) \(\mathrm {photons/s/mrad}^{2}/\mathrm {mm}^{2}/0.1\,\%\,\mathrm {BW}\) in the sub-Angstrom range of the emitted photon wavelengths.

Polarizational Bremsstrahlung in Collisions with Hydrogen Atom

The formulae presented in Chaps. 1 and 2 indicate that to a great extent the behaviour of the total BrS cross