39 research outputs found
Quantum interference between nuclear excitation by electron capture and radiative recombination
We investigate the quantum interference between the resonant process of
nuclear excitation by electron capture (NEEC) followed by the radiative decay
of the excited nucleus, and radiative recombination (RR). In order to derive
the interference cross section, a Feshbach projection operator formalism is
used. The electromagnetic field is considered by means of multipole fields. The
nucleus is described by a phenomenological collective model and by making use
of experimental data. The Fano profile parameters as well as the interference
cross section for electric and magnetic multipole transitions in various heavy
ions are presented. We discuss the experimental possibility of discerning NEEC
from the RR background
Path integral formalism for the free Dirac propagator in spherical coordinates
The relativistic Green's function of a free spin-1/2 fermion is derived using
the Feynman path integral formalism in spherical coordinates. The Green's
function is reduced to an exactly solvable path integral by an appropriate
coordinate transformation. The result is given in terms of spherical Bessel
functions and spherical spinors, and agrees with previous solutions of the
problem
Hadronic vacuum polarization correction to the bound-electron factor
The hadronic vacuum polarization correction to the factor of a bound
electron is investigated theoretically. An effective hadronic Uehling potential
obtained from measured cross sections of annihilation into hadrons is
employed to calculate factor corrections for low-lying hydrogenic levels.
Analytical Dirac-Coulomb wave functions, as well as bound wave functions
accounting for the finite nuclear radius are used. Closed formulas for the
factor shift in case of a point-like nucleus are derived. In heavy ions, such
effects are found to be much larger than for the free-electron factor
Ion Acceleration by Short Chirped Laser Pulses
Direct laser acceleration of ions by short frequency-chirped laser pulses is
investigated theoretically. We demonstrate that intense beams of ions with a
kinetic energy broadening of about 1 % can be generated. The chirping of the
laser pulse allows the particles to gain kinetic energies of hundreds of MeVs,
which is required for hadron cancer therapy, from pulses of energies of the
order of 100 J. It is shown that few-cycle chirped pulses can accelerate ions
more efficiently than long ones, i.e. higher ion kinetic energies are reached
with the same amount of total electromagnetic pulse energy
Astrophysical line diagnosis requires non-linear dynamical atomic modeling
Line intensities and oscillator strengths for the controversial 3C and 3D
astrophysically relevant lines in neonlike Fe ions are calculated. We
show that, for strong x-ray sources, the modeling of the spectral lines by a
peak with an area proportional to the oscillator strength is not sufficient and
non-linear dynamical effects have to be taken into account. Furthermore, a
large-scale configuration-interaction calculation of oscillator strengths is
performed with the inclusion of higher-order electron-correlation effects. The
dynamical effects give a possible resolution of discrepancies of theory and
experiment found by recent measurements, which motivates the use of
light-matter interaction models also valid for strong light fields in the
analysis and interpretation of astrophysical and laboratory spectra.Comment: 5 pages, 3 figure