This dissertation reports on new information in the [beta minus] decay of the neutron-rich nucleus 81Zn, which populates states in its daughter nucleus 81Ga. This includes new [gamma]-ray transitions in the daughter nucleus, 81Ga, as well as a [beta]-delayed neutron branching ratio. This isotope was produced at the Holifield Radioactive Ion Beam Facility of Oak Ridge National Laboratory through the Isotope Separation Online technique. They are fission fragments from proton-induced fission on a uranium carbide target. These fission fragments are ionized and both mass and isotopically separated before arriving at the Low Energy Radioactive Ion Beam Spectroscopy Station (LeRIBSS). The [gamma]-ray and [beta] electron emissions from the decays are measured and analyzed in this work. A new [beta]-delayed neutron branching ratio is reported for this decay, which is in agreement with recent theoretical values. The core excited states in the daughter nucleus, 81Ga, populated through allowed Gamow-Teller decays are analyzed. A trend in core excited states with other N=50 isotones indicates an increasing gap between a deeply bound neutron hole and the valence neutron above the N=50 gap upon moving towards doubly magic 78Ni. This dissertation also reports on additions to the decay schemes of 79Zn and 80Zn decays. Their decay level schemes have been expanded upon and an improved picture of the total allowed Gamow-Teller decay strength is known from 79Zn to 81Zn. This work presents an improved, albeit still incomplete, picture of the energy of states populated through Gamow-Teller decays from below to above the N=50 shell gap in zinc isotopes.

With only two ingredients, atomic nuclei exhibit a rich structure depending on the ordering of the different proton- and neutron-occupied states. This ordering can give rise to excited states with exceptionally long half-lives, also known as isomers, especially near shell closures. On-line mass spectrometry can often be compromised by the existence of such states that may even be produced in higher proportion than the ground state. This thesis presents the first results obtained from a nuclear spectroscopy setup coupled with the high-resolution Penning-trap mass spectrometer ISOLTRAP, at CERN’s radioactive ion beam facility ISOLDE. The isomerism in the neutron-deficient thallium isotopes was investigated. The data on 184,190,193−195 Tl allow an improvement of existing mass values as well as a mass-spin-state assignment in 190,193,194 Tl. Due to the presence of the ground and isomeric state for 194 Tl the excitation energy of the latter was determined for the first time experimentally. Systematic trends in the vicinity of the Z = 82 shell closure have been discussed.

With only two ingredients, atomic nuclei exhibit a rich structure depending on the ordering of the different proton- and neutron-occupied states. This ordering can give rise to excited states with exceptionally long half-lives, also known as isomers, especially near shell closures. On-line mass spectrometry can often be compromised by the existence of such states that may even be produced in higher proportion than the ground state. This thesis presents the first results obtained from a nuclear spectroscopy setup coupled with the high-resolution Penning-trap mass spectrometer ISOLTRAP, at CERN’s radioactive ion beam facility ISOLDE. The isomerism in the neutron-deficient thallium isotopes was investigated. The data on 184,190,193−195 Tl allow an improvement of existing mass values as well as a mass-spin-state assignment in 190,193,194 Tl. Due to the presence of the ground and isomeric state for 194 Tl the excitation energy of the latter was determined for the first time experimentally. Systematic trends in the vicinity of the Z = 82 shell closure have been discussed.

L'étude de la région des noyaux lourds et superlourds représente un des défis de la physique nucléaire contemporaine, tant au niveau des dispositifs expérimentaux nécessaires que des analyses de données complexes. L'étude des noyaux transfermia (Z = 100 à 106) nous permet, au travers de la spectroscopie de décroissance α et γ/électron, d'apporter de nouvelles informations de structure nucléaire ainsi que sur ses propriétés dans cette région de masse. Dans le cadre de ma thèse, j'ai ainsi pu étudier le noyau 257Db. Cette étude a été menée sur le séparateur SHELS auprès du dispositif GABRIELA au JINR de Dubna (Russie). Elle nous a permis d'apporter de nouvelles informations spectroscopiques sur ce noyau au travers d'une étude de spectroscopie retardée en profitant de la réaction de fusion évaporation 50Ti(209Bi,2n)257Db ainsi que les très bonnes performances du dispositif GABRIELA. Ces études ont notamment permis d'établir un nouveau schéma de niveaux pour le noyau 257Db, mais aussi de confirmer le schéma de décroissance pour les noyaux 257Db et 253Lr. De plus, j'ai aussi pris part au développement et à la caractérisation de détecteurs silicium de dernière génération dans le cadre du projet S3/SIRIUS (SPIRAL2, GANIL). Ces études nous ont non seulement permis de caractériser ces détecteurs, et ainsi vérifier leurs performances vis-à-vis du cahier des charges, mais aussi de mettre en évidence des phénomènes internes à basse énergie dans ces derniers. Les caractérisations ainsi que l'analyse et l'interprétation de ces phénomènes sont présentés et discutés. / The study of the heavy and superheavy nuclei mass region represents one of the biggest challenge for the modern nuclear physic regarding both experimental setups and complex analysis. Moreover, the study around the transfermia nuclei (Z = 100 to 106), through the spectroscopy experiments, allows us to bring new information on the nuclear matter and its properties. Therefore, my thesis experiment was focused on the study of the 257Db nuclei. The experiment was performed on the SHELS separator using the GABRIELA setup at the JINR of Dubna (Russia). This study allows us to highlight new information regarding this nucleus, through the delayed spectroscopy method and by using the 50TI(209Bi,2n)257Db fusion evaporation reaction as well as the very good performances of the GABRIELA setup (α, γ and electron detection). This study allows us also to establish a new level scheme as well as to confirm the decay one for the 257Db and 253Lr nuclei. The second part of my thesis work was centered on the development and the characterization of Silicon detectors for the S3/SIRIUS projet (SPRIAL2, GANIL). The characterization allows us to confirm the good performances of these detectors according to the specifications. Moreover, it also highlights internal phenomena at low energy within the detector. Thus, the characterization as well as the interpretation of these phenomena will be presented.