298 research outputs found
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
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
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
QED calculation of the 2p1/2-2s and 2p3/2-2s transition energies and the ground-state hyperfine splitting in lithiumlike scandium
We present the most accurate up-to-date theoretical values of the
{2p_{1/2}}-{2s} and {2p_{3/2}}-{2s} transition energies and the ground-state
hyperfine splitting in . All two- and three-electron
contributions to the energy values up to the two-photon level are treated in
the framework of bound-state QED without \aZ-expansion. The interelectronic
interaction beyond the two-photon level is taken into account by means of the
large-scale configuration-interaction Dirac-Fock-Sturm (CI-DFS) method. The
relativistic recoil correction is calculated with many-electron wave functions
in order to take into account the electron-correlation effect. The accuracy of
the transition energy values is improved by a factor of five compared to the
previous calculations. The CI-DFS calculation of interelectronic-interaction
effects and the evaluation of the QED correction in an effective screening
potential provide significant improvement for the hyperfine splitting. The
results obtained are in a good agreement with recently published experimental
data.Comment: 10 pages, 2 table
Screened self-energy correction to the 2p3/2-2s transition energy in Li-like ions
We present an ab initio calculation of the screened self-energy correction
for (1s)^2 2p3/2 and (1s)^2 2s states of Li-like ions with nuclear charge
numbers in the range Z = 12-100. The evaluation is carried out to all orders in
the nuclear-strength parameter Z \alpha. This investigation concludes our
calculations of all two-electron QED corrections for the 2p3/2-2s transition
energy in Li-like ions and thus considerably improves theoretical predictions
for this transition for high-Z ions
Relativistic recoil, electron-correlation, and QED effects on the 2p_j-2s transition energies in Li-like ions
The relativistic nuclear recoil, higher-order interelectronic-interaction,
and screened QED corrections to the transition energies in Li-like ions are
evaluated. The calculation of the relativistic recoil effect is performed to
all orders in 1/Z. The interelectronic-interaction correction to the transition
energies beyond the two-photon exchange level is evaluated to all orders in 1/Z
within the Breit approximation. The evaluation is carried out employing the
large-scale configuration-interaction Dirac-Fock-Sturm method. The rigorous
calculation of the complete gauge invariant sets of the screened self-energy
and vacuum-polarization diagrams is performed utilizing a local screening
potential as the zeroth-order approximation. The theoretical predictions for
the 2p_j-2s transition energies are compiled and compared with available
experimental data in the range of the nuclear charge number Z=10-60.Comment: 39 pages, 3 figures, 11 table
QED theory of the nuclear recoil effect in atoms
The quantum electrodynamic theory of the nuclear recoil effect in atoms to
all orders in \alpha Z is formulated. The nuclear recoil corrections for atoms
with one and two electrons over closed shells are considered in detail. The
problem of the composite nuclear structure in the theory of the nuclear recoil
effect is discussed.Comment: 20 pages, 6 figures, Late
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