Thanks to advances in production of radioactive nuclear beams in the last two decades, we are able to study nuclear systems very far from stability. The region of the nuclear landscape in the vicinity of 78Ni remains still unexplored. This region, with very neutron-rich 78Ni hypothetically considered as a doubly magic core, is interesting in terms of nuclear structures. The experimental information is equally important to guide the emerging shell-model effective interactions in this region. We have studied -decay of a neutron rich 84Ga isotope at the ALTO facility in IPN Orsay (France). The fission fragments were produced with photo-fission reaction induced by 50 MeV electron beam in a thick UCx target. For the first time the maximum electron driver beam intensity at ALTO - 10uA - was used. The gallium atoms were selectively ionized with a newly developed laser ion source. With this ion source the ionization of the gallium was more than ten times higher compared to the surface ion source previously used by our group. The ions were separated with the PARRNe mass separator and implanted on a movable mylar tape. Two germanium detectors in close geometry were used for the detection of gamma-rays and gamma-gamma coincidence measurement, and a plastic for beta tagging. We present the results of our experiment: the improved level schemes of the neutron-rich 83,84Ge and 84As isotopes. We discuss their structure and compare the experimental results with the shell model calculations made with the new effective interaction ni78-jj4b with 78Ni core, constructed in the framework of this thesis.
