Radioactive isotopes enable advanced medical treatments and the study of nuclear structure, nuclear astrophysics, and fundamental symmetries. TRIUMF, Canada’s Particle Accelerator Centre, generates radioactive isotope beams using the Isotope Separation On-Line method. At TRIUMF, the Forced Electron Beam Induced Arc Discharge (FEBIAD) ion source is used to ionize specific isotopes but often presents limited performance and lower efficiencies compared to other facilities. To investigate the source limitation, elucidate the ionization mechanism, and propose improved and highly efficient sources for upcoming facilities, a combined numerical and experimental campaign has been undertaken. The developed numerical ionization model is able to describe the source as an electron impact ion source that is governed by strong space charge effects. The spatially distributed ionization rate is higher at specific locations of the anode volume, and this has been confirmed experimentally. The validated numerical model has been further used to propose simulation-based optimizations. With the overall optimization, the ionization efficiency for the TRIUMF FEBIAD is expected to increase ten-fold. / Graduate

This work centres around development and applications of the Resonance Ionization Laser Ion Source (RILIS) of the ISOLDE radioactive ion beam facility based at CERN. The RILIS applies step-wise resonance photo-ionization, to achieve an unparalleled degree of element selectivity, without compromising on ion source efficiency. Because of this, it has become the most commonly used ion source at ISOLDE, operating for up to 75% of ISOLDE experiments. In addition to its normal application as an ion source, the RILIS can be exploited as a spectroscopic tool for the study of nuclear ground state and isomer properties, by resolving the influence of nuclear parameters on the atomic energy levels of the ionization scheme. There are two avenues of development by which to widen the applicability of the RILIS: laser ionization scheme development, enabling new or more efficient laser ionized ion beams and the development of new laser-atom interaction regions. New ionization schemes for chromium, tellurium, germanium, mercury and radium have been determined. Additionally, for the first time, the anode cavity of the VADIS, ISOLDE's variant of the FEBIAD type arc discharge ion source was used as the laser-atom interaction region. A new element selective RILIS mode of operation was established, enabling the ISOLDE RILIS to be coupled with molten targets for the first time, increasing the flexibility of ISOLDE operation and opening a direction for future developments. This combined ion source was termed the VADLIS or Versatile Arc Discharge and Laser Ion Source. A combination of the developments presented in this thesis: an improvement of the laser ionization efficiency and the ability to couple the RILIS with molten targets, satisfied the pre-requisites for the long-awaited extension of the laser spectroscopy studies of exotic mercury isotopes. A sudden onset of extreme shape staggering in the neutron deficient mercury isotopes was revealed by optical pumping and laser spectroscopy experiments at ISOLDE in the 1970s and 1980s, with measurements conducted down to 181Hg. Despite this being one of the most remarkable examples of shape coexistence in the nuclear chart, in the intervening decades the cessation point of this odd-even staggering had yet to be unambiguously determined through measurements of nuclear ground state charge radii. This open question was successfully resolved using the ISOLDE RILIS for in-source resonance ionization spectroscopy. The experiment was performed as part of a large collaboration, using the Leuven Windmill system for alpha-detection; direct ion counting with the ISOLTRAP multi-reflection time-of-fight mass spectrometer (MR-ToF MS); and ion beam current measurements using the ISOLDE Faraday cups. The sensitivity of the technique enabled the measurements to be extended down to 177Hg, providing a definitive answer, that the extreme shape staggering stops at 180Hg. In addition to extending the measurements at the neutron deficient end of the mercury isotope chain, the relative mean square charge radii of both 207Hg and 208Hg was determined. This extended the measurements beyond the N = 126 shell closure, enabling the characterization of the "kink" in the trend of the isotope shifts.

Ce travail de thèse s'inscrit dans le cadre du projet ALTO (Accélérateur Linéaire Auprès du Tandem d'Orsay), projet exploitant la photofission comme mode de production de noyaux riches en neutrons pour la séparation en ligne. Nos travaux portent sur l'étude des modes d'adaptation de l'environnement de production représenté par son ensemble cible-source d'ions.<br /> Nous avons mené une étude exhaustive de radioprotection pour dimensionner et définir la nature des blindages nécessaires pour faire face aux flux intenses de photons et de neutrons générés dans la cible de production.<br /> Les simulations Monte Carlo avec le code FLUKA nous ont permis de calculer le transport simultané des photons et des neutrons avec une modélisation intégrale des structures géométriques très complexes. Pour l'ensemble cible-source d'ions et les points critiques de pertes de faisceaux, nous proposons des blindages optimisés basés essentiellement sur la structure segmentée.<br /> Nous avons étudié l'adéquation d'une cible épaisse de carbure d'uranium pour la production de noyaux radioactifs riches en neutrons par photofission. En particulier, nous avons montré la validité du code FLUKA pour la photofission avec un faisceau d'électrons de 50 MeV, en comparant les résultats de calculs aux mesures expérimentales réalisées.<br /> Enfin, nous présentons nos travaux de conception et de développement d'un prototype de source d'ions de type FEBIAD destinée aux installations de seconde génération : la source IRENA. Ces travaux montrent à quel point les considérations de radioprotection sont également impliquées dans le développement de la source.