1,004 research outputs found
Hyperfine-induced effects on the linear polarization of the K emission from helium-like ions
The linear polarization of the characteristic photon emission from
few-electron ions is studied for its sensitivity with regard to the nuclear
spin and magnetic moment of the ions. Special attention is paid, in particular,
to the K (1s 2p_{3/2} ^{1,3}P_{1,2} \to 1s^2 ^1S_0) decay of
selected helium-like ions following the radiative electron capture into
initially hydrogen-like species. Based on the density matrix theory, a unified
description is developed that includes both, the many-electron and hyperfine
interactions as well as the multipole-mixing effects arising from the expansion
of the radiation field. It is shown that the polarization of the K
line can be significantly affected by the mutipole mixing between the leading
and hyperfine-induced components of 1s2p ^3P_2, F_i \to 1s^2 ^1S_0,
F_f transitions. This - mixing strongly depends on the nuclear
properties of the considered isotopes and can be addressed experimentally at
existing heavy-ion storage rings
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
Many-electron effects on the x-ray Rayleigh scattering by highly charged He-like ions
The Rayleigh scattering of x-rays by many-electron highly charged ions is
studied theoretically. The many-electron perturbation theory, based on a
rigorous quantum electrodynamics approach, is developed and implemented for the
case of the elastic scattering of (high-energetic) photons by helium-like ion.
Using this elaborate approach, we here investigate the many-electron effects
beyond the independent-particle approximation (IPA) as conventionally employed
for describing the Rayleigh scattering. The total and angle-differential cross
sections are evaluated for the x-ray scattering by helium-like Ni,
Xe, and Au ions in their ground state. The obtained results
show that, for high-energetic photons, the effects beyond the IPA do not exceed
2% for the scattering by a closed -shell.Comment: 15 pages, 11 figure
Momentum-resolved study of the saturation intensity in multiple ionization
We present a momentum-resolved study of strong field multiple ionization of
ionic targets. Using a deconvolution method we are able to reconstruct the
electron momenta from the ion momentum distributions after multiple ionization
up to four sequential ionization steps. This technique allows an accurate
determination of the saturation intensity as well as of the electron release
times during the laser pulse. The measured results are discussed in comparison
to typically used models of over-the-barrier ionization and tunnel ionization
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
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