298 research outputs found
Double lepton pair production with electron capture in relativistic heavy--ion collisions
We present a theoretical study of a double lepton pair production in
ultra--relativistic collision between two bare ions. Special emphasis is placed
to processes in which creation of (at least one) pair is accompanied
by the capture of an electron into a bound ionic state. To evaluate the
probability and cross section of these processes we employ two approaches based
on (i) the first--order perturbation theory and multipole expansion of Dirac
wavefunctions, and (ii) the equivalent photon approximation. With the help of
such approaches, detailed calculations are made for the creation of two
bound--free pairs as well as of bound--free and free--free
pairs in collisions of bare lead ions Pb. The results of
the calculations indicate that observation of the double lepton processes may
become feasible at the LHC facility.Comment: 12 pages, 1 figur
Negative-continuum dielectronic recombination into excited states of highly-charged ions
The recombination of a free electron into a bound state of bare, heavy
nucleus under simultaneous production of bound-electron--free-positron pair is
studied within the framework of relativistic first--order perturbation theory.
This process, denoted as "negative-continuum dielectronic recombination" leads
to a formation of not only the ground but also the singly- and doubly-excited
states of the residual helium-like ion. The contributions from such an
excited--state capture to the total as well as angle-differential
cross-sections are studied in detail. Calculations are performed for the
recombination of (initially) bare uranium U ions and for a wide range
of collision energies. From these calculations, we find almost 75 % enhancement
of the total recombination probability if the excited ionic states are taken
into account.Comment: 8 pages, 4 figures, accepted to PR
Target effects in negative-continuum assisted dielectronic recombination
The process of recombination of a quasi-free electron into a bound state of
an initially bare nucleus with the simultaneous creation of a
bound-electron--free-positron pair is investigated. This process is called the
negative-continuum assisted dielectronic recombination (NCDR). In a typical
experimental setup, the initial electron is not free but bound in a light
atomic target. In the present work, we study the effects of the atomic target
on the single and double-differential cross sections of the positron production
in the NCDR process. The calculations are performed within the relativistic
framework based on QED theory, with accounting for the electron-electron
interaction to first order in perturbation theory. We demonstrate how the
momentum distribution of the target electrons removes the non-physical
singularity of the differential cross section which occurs for the initially
free and monochromatic electrons
Solution of two-center time-dependent Dirac equation in spherical coordinates: Application of the multipole expansion of the electron-nuclei interaction
A non-perturbative approach to the solution of the time-dependent, two-center
Dirac equation is presented with a special emphasis on the proper treatment of
the potential of the nuclei. In order to account for the full multipole
expansion of this potential, we express eigenfunctions of the two-center
Hamiltonian in terms of well-known solutions of the "monopole" problem that
employs solely the spherically-symmetric part of the interaction. When combined
with the coupled-channel method, such a wavefunction-expansion technique allows
for an accurate description of the electron dynamics in the field of moving
ions for a wide range of internuclear distances. To illustrate the
applicability of the proposed approach, the probabilities of the K- as well as
L- shell ionization of hydrogen-like ions in the course of nuclear alpha-decay
and slow ion-ion collisions have been calculated
Inter-electronic interaction effects on the polarization of recombination photons
A theoretical investigation of the radiative capture of an electron into a
bound state of heavy, hydrogen-like ion is presented. Special attention is paid
to the question of how the linear polarization of the emitted radiation is
affected by the inter-electronic interaction effects. An analysis of these
effects is performed within both, the screening-potential approximation and the
perturbation theory that treats rigorously the electron correlations to the
first order in the parameter 1/Z. By making use of these two approaches,
detailed calculations are performed for relativistic collisions of
hydrogen-like europium Eu^{62+}, bismuth Bi^{82+} and uranium U^{91+} ions with
free electron and low-Z atomic targets. Results of the calculations indicate
that the two-electron effects may significantly influence the polarization
properties of the recombination x-rays; the effect which can be observed by the
present-day polarization detectors
QED calculation of the 2p3/2-2p1/2 transition energy in five-electron ion of argon
We perform ab initio QED calculation of the (1s)^2(2s)^22p_{3/2} -
(1s)^2(2s)^22p_{1/2} transition energy in the five-electron ion of argon. The
calculation is carried out by perturbation theory starting with an effective
screening potential approximation. Four different types of the screening
potentials are considered. The rigorous QED calculations of the two
lowest-order QED and electron-correlation effects are combined with approximate
evaluations of the third- and higher-order electron-correlation contributions.
The theoretical value for the wavelength obtained amounts to 441.261(70) (nm,
air) and perfectly agrees with the experimental one, 441.2559(1) (nm, air).Comment: 10 pages, 3 figures, 1 tabl
Quantum electrodynamics of heavy ions and atoms
The present status of quantum electrodynamics (QED) theory of heavy
few-electron ions is reviewed. The theoretical results are compared with
available experimental data. A special attention is focused on tests of QED at
strong fields and on determination of the fundamental constants. A recent
progress on calculations of the QED corrections to the parity nonconserving
6s-7s transition amplitude in neutral Cs is also discussed.Comment: Talk at ICAP 2006, Innsbruck, Austri
Young-type interference in projectile-electron loss in energetic ion-molecule collisions
Under certain conditions an electron bound in a fast projectile-ion,
colliding with a molecule, interacts mainly with the nuclei and inner shell
electrons of atoms forming the molecule. Due to their compact localization in
space and distinct separation from each other these molecular centers play in
such collisions a role similar to that of optical slits in light scattering
leading to pronounced interference in the spectra of the electron emitted from
the projectile.Comment: 4 pages, 3 figure
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