44 research outputs found
Invariant Time-Dependent Exchange Perturbation Theory and its Application to the Particles Collision Problem
We present the formalism of Time-dependent Exchange Perturbation Theory
(TDEPT) built to all orders of perturbation, for the arbitrary time dependency
of perturbation. The theory takes into account the rearrangement of electrons
among centres. We show how the formalism can be reduced to the standard form of
invariant perturbation theory by 'switching off' the re-arrangement of
electrons among centres. The elements of the scattering S-matrix and
transitions T-matrix and the formula for the electron scattering differential
cross section are derived. The application of the theory to scattering and
collision problems is discussed. As an example, we apply the theory to proton
scattering on a Lithium atom, calculating the differential and total
cross-sections
Influence of absorbed energy distribution along beam radius on ignition threshold of condensed explosives
The criterion of the condensed explosive ignition by the electron beam, which takes into account Gaussian distribution of electron density along the beam radius, has been obtained. It has been shown that radial heat removal of the absorbed energy leads to the increase in critical ignition energy if the effective track length of electrons in a solid is commensurate with the beam radius. The critical energy of PETN initiation by the electron beam has been calculated
Permutation Symmetry in Coherent Electrons Scattering by Disordered Media
A non-Anderson weak localization of an electron beam scattered from disordered matter is considered with respect to the principle of electron indistinguishability. A weak localization of electrons of a new type is essentially associated with inelastic processing. The origin of inelasticity is not essential. We take into account the identity principle for electron beam and electrons of the atom of the scatterer with an open shell. In spite of isotropic scattering by each individual scatterer, the electron exchange contribution has a hidden parameters effect on the resulting angular dependence of the scattering cross-section. In this case, the electrons of the open shell of an atomic scatterer can be in the s-state, that is, the atomic shell remains spherically symmetric. The methods of an invariant time-dependent exchange perturbation theory and a Green functions with exchange were applied. An additional angular dependence of the scattering cross-section appears during the coherent scattering process. It is shown exactly for the helium scatterer that the role of exchange effects in the case of a singlet is negligible, while for the triplet state, it is decisive, especially for those values of the energy of incident electrons when de Broglie’s waves are commensurate with the atomic
Collision of a Positron with the Capture of an Electron from Lithium and the Effect of a Magnetic Field on the Particles Balance
The processes of scattering slow positrons with the possible formation of positronium play an important role in the diagnosis of both composite materials, including semiconductor materials, and for the analysis of images obtained by positron tomography of living tissues. In this paper, we consider the processes of scattering positrons with the capture of an electron and the formation of positronium. When calculating the cross-section for the capture reaction, exchange effects caused by the rearrangement of electrons between colliding particles are taken into account. Comparison of the results of calculating the cross-section with a similar problem of electron capture by a proton showed that the mass effect is important in such a collision process. The loss of an electron by a lithium atom is more effective when it collides with a positron than with a proton or alpha particles. The dynamic equilibrium of the formation of positronium in the presence of a strong magnetic field is considered. It is shown that a strong magnetic field during tomography investigation shifts the dynamic equilibrium to the positronium concentration followed by positron annihilation with radiation of three gamma-quants
Influence of spin-orbit interaction on magnetic properties of fullerenes
The current paper is devoted to the consideration of sp2-carbonaceous
fullerenes molecules in a homogeneous magnetic field. Due to a reduction system symmetry
in the magnetic field, the energy splitting gives rise dominant atomic structures in
fullerene molecules with local symmetries. Spin-orbit interaction plays a crucial role in
this phenomenon. The current paper is aimed at determine spin-orbit coupling parameters,
as an energy ESO and a constant aSO as well as a
Lande g-factor for the C60-based compounds in the
magnetic field