Study of the isomeric states in the superheavy nuclei: particular case of the ²⁵⁷Db and ²⁵³Lr nuclei

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 project (SPIRAL2, 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. (author)