CONFIGURATION MIXING INVESTIGATION IN GERMANIUM ISOTOPES

Protons and neutrons of atomic nuclei can arrange in both spherical and non-spherical configurations. Nuclei can also exhibit configurations which lie close in energy, yet present different deformations. Such phenomenon is referred to as shape coexistence and its occurrence in nuclei is thought to pervade the entire nuclear chart. Excited states with similar energies and same spin and parity can also mix, so that the observed states are the result of mixing of different configurations. In this context, the structure of Ge isotopes has been widely investigated over the years. Previous transfer reaction experiments pointed to the occurrence of configuration mixing between the ground state and first excited 0+ state in 72Ge (N = 40). Furthermore, they indicated a weakening of such mixing moving away from N = 40, in correspondence with the increase of the excitation energy of the 0+[2] state. However, the nature of the configurations that mix and their evolution along the Ge isotopic chain is still elusive. In this thesis, a study of configuration mixing in the even-even Ge isotopes at and near stability (A = 72, 74, 76, 78) has been carried out through the measurement of electric monopole (E0) transition strengths, which have been identified as a sensitive probe of configuration mixing. In particular, the focus has been set on the transitions with I = 2, 2+[2]→2+[1]. The experiments presented in this thesis have been performed at the TRIUMF laboratory (Vancouver, Canada). The isotopes of interest have been populated via the β decay of radioactive ion beams of 72,74,76,78Ga, which were implanted at the center of the GRIFFIN decay station. The GRIFFIN spectrometer, combined with the PACES silicon array, enabled us to perform both γ-ray and electron spectroscopic investigations, to measure E0 strengths between states with I = 2.