Search for deformation in neutron-rich nuclei

Nowadays, the atomic nucleus is used in a variety of common way. Nevertheless, this object is not fully understood yet. This is why nuclear physics research is still needed. Among the large number of nuclear physics topics, this work is interested in the study of shape changes in neutron-rich Ru and Sr isotopes. The subject is figured out in the first chapter, dealing with theoretical concepts about nuclear physics. A second chapter describes the experiment permitting to produce the isotopes of interest. This γ-ray spectroscopy experiment has been realized with a HPGe multidetector made from EXOGAM and completed by GASP and LOHENGRIN detectors. This experiment uses the fission of ²⁴¹Pu induced by cold neutron, supplied by the reactor of the Institute Laue-Langevin. This experiment is a part of the EXILL measurement campaign. The second chapter also deals with the data pre-analysis. After showing the effects of a multiplicity cut on event preselection, the obtained results concerning ¹⁰⁸Ru to ¹¹⁵Ru and ⁹²Sr to ⁹⁶Sr isotopes are presented in the third chapter. Finally, the fourth chapter puts these results in a wider part of the neutron-rich side of both isotope series. These last ones are also placed in their mass region context. The region of interest is rich in shape changes, whether with neutronic enrichment or with excitation energy. These changes are rather well described by certain models, but the latter still have difficulties to describe the limits. Their precise determinations by experiment are essential to constrain models. (author)