Theoretical and Experimental Investigation of 156Gd Nucleus at Low-Energy Region

The Jpi = 1+ scissor mode was first observed in 156Gd in high-resolution electron scattering experiments in 1984 and shortly after confirmed by (e,e') Nuclear Resonance Fluorescence (NRF) experiment. In this thesis, an experiment was performed at the superconducting Darmstadt linear electron accelerator (S-DALINAC) using the NRF technique to study dipole-excitations of 156Gd up to 7 MeV. A monoenergetic electron beam of 7.1 Mev was used for the production of bremsstrahlung allowing the investigation of dipole excitations of 156Gd in the sensitive energy range of 3 to 7 MeV. The technique of NRF allows for the recovery of several physical quantities characterizing the excited nuclear states in a completely model independent way. These observables include the excitation energies, level widths, gamma decay branching ratios, spin quantum numbers, and parities. In total, 70 excited states of 156Gd were observed in the energy range up to 7 MeV. Some of these states have been observed in an (gamma, gamma') experiment for the first time in this experiment subject to this thesis. On the theoretical side of this thesis, the Bohr Hamiltonian with the well-known Generalized Woods-Saxon potential involving the repulsive angular momentum barrier is solved analytically to explain experimental observables of 156Gd lying in the shape-phase transition region. We observe a good agreement between calculated and experimental values for energy spacing within the ground state and gamma-band for the 156Gd nucleus.