Nuclear structure studies on quadrupole and octupole correlations in the vicinity of heavy n=z nuclei with agata and neda

Zusammenfassung

The evolution of collectivity is essential to understand the structure of nuclei far from stability.The region that lies just above the Z=50 closed shell, in the vicinity of N=Z, exhibits interesting collective properties of quadrupole and octupole character. The aim of this thesis is to study the evolution of the quadrupole and octupole collectivity in light Xe isotopes, when approaching the N=Z line, through the lifetime measurement of the low laying excited states of 112Xe where the reduced transitions probabilities were determined. The collectivity in Xe isotopes when neutrons are removed increases until the mid-shell for neutrons around N=66 as decrease until N=58 where there is a change in the trend and the collectivity in the light Xe seems to persist. To investigate the evolution of collectivity, the quadrupole degree of freedom is studied through the lifetime of the 2+ and 4+ states in the 112Xe nucleus measured for the first time. The experiment was performed in the first campaign with the AGATA-NEDA+NW-DIAMANT setup installed at the GANIL laboratory, with the CSNSM “OUPS” plunger device. A fusion evaporation reaction was used to populate the 112Xe with a 58Ni beam, with an energy of 250 MeV, impinging on a 58Ni 1 mg/cm2 target. A 197Au degrader with a thickness of 5 mg/cm2 was installed in the plunger device to degrade the reaction products energy without stopping them, in order to maximize the energy resolution. The experiment was performed with a trigger condition of one neutron identified in NEDA-NW in coincidence with two detectors in AGATA while the information of DIAMANT has been used off-line for identification of the channels. The reduced transitions probabilities for the 4+ → 2+ and 2+ → 0+ transitions in 112Xe have been determined and compared with different theoretical models; LSSM, BMF and TRS. In addition, the reduced transition probability for the 5- → 4+ transition is determined and an upper limit for the reduced transition probability for 5- → 2+ transition could be determined. Futhermore, the final part of the thesis is dedicated to my contribution of the construction of the NEDA detectors at INFN-LNL to be used in a campaign for measurements, including the experiment described in the thesis.