350 research outputs found
Relativistic configuration-interaction calculation of energy levels of core-excited states in lithium-like ions: argon through krypton
Large-scale relativistic configuration-interaction calculation of energy
levels of core-excited states of lithium-like ions is presented. Quantum
electrodynamic, nuclear recoil, and frequency-dependent Breit corrections are
included in the calculation. The approach is consistently applied for
calculating all core-excited states for all lithium-like ions starting
from argon () and ending with krypton (). The results obtained
are supplemented with systematical estimations of calculation errors and
omitted effects
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
Compton scattering of twisted light: angular distribution and polarization of scattered photons
Compton scattering of twisted photons is investigated within a
non-relativistic framework using first-order perturbation theory. We formulate
the problem in the density matrix theory, which enables one to gain new
insights into scattering processes of twisted particles by exploiting the
symmetries of the system. In particular, we analyze how the angular
distribution and polarization of the scattered photons are affected by the
parameters of the initial beam such as the opening angle and the projection of
orbital angular momentum. We present analytical and numerical results for the
angular distribution and the polarization of Compton scattered photons for
initially twisted light and compare them with the standard case of plane-wave
light
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
Comparative study of the electron- and positron-atom bremsstrahlung
Fully relativistic treatment of the electron-atom and positron-atom
bremsstrahlung is reported. The calculation is based on the partial-wave
expansion of the Dirac scattering states in an external atomic field. A
comparison of the electron and positron bremsstrahlung is presented for the
single and double differential cross sections and the Stokes parameters of the
emitted photon. It is demonstrated that the electron-positron symmetry of the
bremsstrahlung spectra, which is nearly exact in the nonrelativistic regime, is
to a large extent removed by the relativistic effects
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
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
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