Investigations of the PYGMY dipole resonance in semi-magic and deformed even-even nuclei

In this thesis, Pygmy Dipole Resonance (PDR) excitations for even-even semi-magic 110-124Sn isotopes and deformed 146-152Nd, 148-154Sm and 236,238U isotopes, both PDR and Giant Dipole Resoans (GDR) excitations for 232Th isotope has been examined for the first time so detailed and systematic on the basis of QRPA (Quasiparticle Random Phase Approach). Besides, magnetic dipole excitation was investigated for the odd mass 161Dy isotope in basis of QPNM (Quasiparticle-Phonon Nuclear Model). According to the 1+ and 1- cases of these nucleus isotopes, reduced transition B(π1) probability, radiation widhts (π1), reduced radiation widhts red(π1), photon scattering cross-sections , have computed by QRPA and QPNM methods. In addition, the effects of restoring rotational, translational and Galilean symmetry forces were considered. The structure of the PDR mode in deformed nuclei has been firstly studied so systematically. The nn-pp structure of the PDR and GDR mode have been compared and the structure of these two modes have been revealed to be different from each other. Electric and magnetic dipole transition probabilities are calculated separately and are distinguished from each other. In this context, the parity distinction, which cannot be distinguished in the experiments, has been done theoretically. The results obtained from this theory are compared with the available experimental data.