Computational Atomic Structure: Applications to Astrophysics and Nuclear Structure

This thesis deals with the modelling of atoms and ions. In heavy systems, where the effect of the nuclear size must be considered, a fully relativistic treatment based on the Dirac-Coulomb Hamiltonian is needed. Chapter two of the thesis provides an introduction to the basic principles of the fully relativistic multiconfiguration Dirac-Hartree-Fock (MCDHF) method, which is a variational approach for determining the wave functions. After we demonstrate how to obtain the best approximation of the wave functions by optimizing the energy expression, we describe how to compute the eigenvalues of operators other than the Hamiltonian, and how these eigenvalues correspond to measurable quantities. Chapter three and four, respectively, summarize the work done in the two published papers, illustrating some of the applications of the relativistic atomic structure theory.Paper I is an example of atomic structure calculations for astrophysical applications. Extensive amount of atomic transition data are produced for the systems of neutral and singly ionized aluminium that can be used to improve the interpretation of abundances in stars. Paper II demonstrates a novel method, in which the atomic structure calculations of isotope shifts are combined with experimental data, for extracting nuclear properties other than the charge radii

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 Landé 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

Structural trends in atomic nuclei from laser spectroscopy of tin

Tin is the chemical element with the largest number of stable isotopes. Its complete proton shell, comparable with the closed electron shells in the chemically inert noble gases, is not a mere precursor to extended stability; since the protons carry the nuclear charge, their spatial arrangement also drives the nuclear electromagnetism. We report high-precision measurements of the electromagnetic moments and isomeric differences in charge radii between the lowest 1/2(+), 3/2(+), and 11/2(-) states in Sn117-131, obtained by collinear laser spectroscopy. Supported by state-of-the-art atomic-structure calculations, the data accurately show a considerable attenuation of the quadrupole moments in the closed-shell tin isotopes relative to those of cadmium, with two protons less. Linear and quadratic mass-dependent trends are observed. While microscopic density functional theory explains the global behaviour of the measured quantities, interpretation of the local patterns demands higher-fidelity modelling. Measurements of the hyperfine structure of chemical elements isotopes provide unique insight into the atomic nucleus in a nuclear model-independent way. The authors present collinear laser spectroscopy data obtained at the CERN ISOLDE and measure hyperfine splitting along a long chain of odd-mass tin isotopes.Peer reviewe

Effect of realistic nuclear charge distributions on isotope shifts and progress towards the extraction of higher-order nuclear radial moments

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. The purpose of this work is to investigate how sensitive field shifts are with respect to variations in the nuclear size and shape and what information of nuclear charge distributions can be extracted from measurements. 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 and it is seen that phenomena such as nuclear deformation and variations in the diffuseness of nuclear charge distributions give measurable contributions to the isotope shifts. Using a different approach, we demonstrate the possibility to extract information concerning the nuclear charge densities from the observed field shifts. We deduce that combining methods used in atomic and nuclear structure theory gives an improved description of field shifts and that extracting additional nuclear information from measured isotope shifts is possible in the near future with improved experimental methods

Ab initio electronic factors of the A and B hyperfine structure constants for the 5s(2)5p6s( 1,3)P(1)(0) states in Sn I

Large-scale ab initio calculations of the electronic contribution to the electric quadrupole hyperfine constant B were performed for the 5s(2)5p6s( 1,3)P(1)(0)excited states of neutral tin. To probe the sensitivity of B to different electron correlation effects, three sets of variational multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction calculations employing different strategies were carried out. In addition, a fourth set of calculations was based on the configuration interaction Dirac-Fock-Sturm theory. For the 5s(2)5p6s( 1)P(1)(0) state, the final value of B/Q = 703(50) MHz/b differs by 0.4% from the one recently used by Yordanov et al. [Commun. Phys. 3, 107 (2020)] to extract the nuclear quadrupole moments Q for tin isotopes in the range Sn117-131 from collinear laser spectroscopy measurements. Efforts were made to provide a realistic theoretical uncertainty for the final B/Q value of the 5s(2)5p6s( 1)P(1)(0) state based on statistical principles and on correlation with the electronic contribution to the magnetic dipole hyperfine constant A.Peer reviewe

Computational atomic structure with GRASP towards heavy atoms and ions of astrophysical interest

info:eu-repo/semantics/nonPublishe

Generation of entanglement using a short-wavelength seeded free-electron laser

International audienceEntanglement between massive particles is a purely quantum mechanical phenomenon with no counterpart in classical physics. Although polarized photons are suitable for applications of quantum entanglement over large distances, fundamental studies of entanglement in massive objects are often conducted for confined quantum systems, such as superconductors, quantum dots, and trapped ions. Here, we generate entanglement in a novel bipartite quantum system containing two massive objects: a photoelectron, which is a free particle propagating rapidly in space, and a light-dressed atomic ion with tunable coupled energy levels. Because of the entanglement, the measured photoelectron spectra reveal information about the coherent dynamics in the residual ion interacting with femtosecond extreme ultraviolet pulses delivered by a seeded free-electron laser. The observations are supported by a quantum optics based analytical model, which was further validated by numerical simulations based on the time-dependent Dirac equation. The degree of entanglement between the two objects is interpreted in terms of the entanglement entropy of the reduced system, as a function of the interaction time between the laser pulse and the dressed ion. Our results uncover the potential for using short-wavelength coherent light pulses from free-electron lasers to generate entangled photoelectron and ion systems for studying `spooky' action at a distance across ultrafast timescales