SHAPE COEXISTENCE IN EVEN-EVEN SN NUCLEIWITH MASS NUMBER A=110-120

Shape coexistence is a ubiquitous phenomenon across the nuclear chart, characterized by the appearance of states with different intrinsic shapes at similar excitation energies. In tin isotopes (Z=50), theoretical models predict such coexisting excitations, and experimental evidence for intruder configurations was first observed in the 70s. Nevertheless, spectroscopic information on low-lying 0⁺ excited states, essential to shed light on the onset of shape coexistence in this region, has remained limited. This PhD thesis presents a systematic study of low-lying 0⁺ excitations in even-even 110-120Sn isotopes, combining γ-ray spectroscopy with lifetime measurements. A series of experiments was performed at the Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering (IFIN-HH) with the ROSPHERE-SORCERER setup and at the Legnaro National Laboratory (LNL) with the AGATA-PRISMA setup, employing heavy-ion transfer reactions to populate excited states. Particle-γ coincidence techniques enabled detailed spectroscopic studies, while lifetime measurements were performed using the Doppler Shift Attenuation Method and the Recoil Distance Doppler Shift method. The deduced transition probabilities significantly expand the experimental knowledge of 0⁺ states in this mass region, revealing systematic trends that support strong configuration mixing and the presence of coexisting shapes. These findings provide important constraints for modern nuclear-structure models and contribute to a deeper understanding of shape coexistence in medium-heavy nuclei.