  Background: Atomic spectral lines from different isotopes display a small
shift in energy, commonly referred to as the line isotope shift. One of the
components of the isotope shift is the field shift, which depends on the extent
and the shape of the nuclear charge density distribution. Purpose: To
investigate how sensitive field shifts are with respect to variations in the
nuclear size and shape and what information of nuclear charge distributions
that can be extracted from measured field shifts. Methods: Nuclear properties
are obtained from nuclear density functional theory calculations based on the
Skyrme-Hartree-Fock-Bogoliubov approach. These results are combined with
multiconfiguration Dirac-Hartree-Fock methods to obtain realistic field shifts.
Results: Phenomena such as nuclear deformation and variations in the
diffuseness of nuclear charge distributions give measurable contributions to
the field shifts. Using a novel approach, we demonstrate the possibility to
extract new information concerning the nuclear charge densities from the
observed field shifts. Conclusions: Combining methods used in atomic and
nuclear structure theory gives an improved description of field shifts.
Extracting additional nuclear information from measured field shifts is
possible in the near future with improved experimental methods.
