Search for large nuclear deformations in spin and isospin exotic nuclei by means of the EUROBALL IV and EXOGAM γ multidetectors

This work is devoted to the study of heavy nuclei under extreme conditions of spin and isospin. Several experiments were done with the γ multidetectors EUROBALL IV and EXOGAM located, at the IReS Strasbourg VIVITRON accelerator and at the GANIL-Caen facility, respectively. The nuclei of interest have been populated using fusion-evaporation reactions. New methods of analysis and programs based on fuzzy logic theory have been developed. Two experiments have been carried out with EUROBALL IV to study the superdeformed nuclei in the A ∼ 190-200 mass region and, in particular, the superdeformed structure of the ^197,198Pb and ¹⁹⁶Bi nuclei. In the first case, the six discovered new bands suggest a coupling between octupole vibration and intrinsic excitations. In the second case we have observed the lowest energy superdeformed γ transition except the fission isomers. These results have been discussed in terms of microscopic self-consistent mean-field calculations carried out in collaboration with theoretical physicists of the IPN Lyon and SPTh/Saclay laboratories. The last part of this work deals with the search of large deformation in the rare-earth nuclei of the A ∼ 120 - 130 mass region located near the proton drip line. This experiment has been carried out with the EXOGAM γ multidetector coupled to the light charged particle detector DIAMANT and using a ⁷⁶Kr radioactive beam from SPIRAL. (author)