Atomic Electrons as Sensitive Probes of Nuclear Properties and Astrophysical Plasma Environments: A Computational Approach

This thesis deals with the relativistic modeling of atoms and ions. To interpret the stellar spectra and gain more insight from astrophysical observations, the underlying processes that generate the spectra need to be well understood and described. Examples of such processes are the interactions of atomic electrons with internal and external electromagnetic fields and with the nucleus.By exploring different computational methodologies, Paper I analyzes how the transition probabilities, of transitions involving high Rydberg states, depend on the gauge and the orbital set that is used in the calculations. Papers II and III contain large homogeneous data sets of parameters related to atomic radiative processes, namely transition energies, transition probabilities, weighted oscillator strengths, and lifetimes of excited states, for carbon and aluminium systems. These parameters are essential in astrophysical applications, e.g., in abundance and plasma analyses of stars. In addition, Paper IV presents extended data of Lande g-factors, used to characterize the response of spectral lines to a given value of an external magnetic field. The description of effects arising from the interplay between atomic electrons and nuclei, such as hyperfine structure splittings and isotope shifts, requires that the nuclear structure properties giving rise to these effects are well determined. This is, however, not always the case; as we move away from the valley of stability, data of nuclear structure observables are scarce. High-resolution measurements of hyperfine structures and isotope shifts, combined with first-principles atomic structure calculations, are commonly used to probe the structures of nuclei, including short-lived and radioactive systems. In Papers V and VI, measurements of the hyperfine structure in neutral tin were combined with atomic structure calculations to extract the electric quadrupole moments of tin isotopes. Paper VII presents a novel method that combines experimental isotope shifts and calculations of atomic parameters to probe details of nuclear charge density distributions, other than charge radii. (Less)