RELATIVISTIC COULOMB EXCITATION OF NEUTRON RICH FE AND NI ISOTOPES

This PhD thesis discusses the measurement of E1 strength around one particle separation energy in exotic neutron rich Iron and Nickel isotopes using the relativistic coulomb excitation. The state of the art of detectors array was used in this measurement: the AGATA segmented HPGe detector array, the DALI2 array and the HECTOR+  large volume scintillator detector array. Relativistic coulomb excitation is a well established experimental technique to investigate the properties of nuclear structure: in particular the E1 isovector response of nuclei. The electric dipole response of neutron rich nuclei around the one particle separation energy (6-12 MeV energy range) is presently the subject of a large experimental and theoretical effort. In this energy region structures and accumulations of E1 strength were measured in a variety of nuclei along all the valley of stability. These structures, commonly called Pygmy Dipole Resonance (PDR), are at the centre of a scientific debate as the strength is connected to the neutron skin thickness and the symmetry energy term of the nuclear equation of state. The relevance of these aspects motivated the investigation of PDR in exotic nuclei. In fact, in spite of the large amount of data about E1 strength distribution in stable nuclei, very few data are available for neutron rich exotic nuclei. In this work the measurement of PDR states in 64;62 Fe and 70 Ni nuclei is presented and discussed in details. The Iron isotope investigation was performed in GSI in 2012 and concluded in 2014, during the PreSPEC  AGATA experimental campaing, while the 70 Ni E1 response was measured at the RIKEN/RIBF laboratory during the DALI2 campaign in autumn 2014. Neutron rich isotopes are expected to be characterized by an enhancement of these PDR structures because of a more unbalanced neutron over proton number ratio. The results of this measurement, here reported, is therefore an important test benchmark for the theories developed to explain these structures.