Investigation of the electric dipole (E1) excitations in Ta-181 nucleus

E1 transition properties such as the reduced transition probabilities, excitation energies and photon-absorption cross-sections have been theoretically investigated for Ta-181 nucleus within the framework of Translational and Galileo Invariant-Quasiparticle Phonon Nuclear Model (TGI-QPNM). The model Hamiltonian includes the single-particle and the isovector dipole-dipole interaction terms along with the restoration forces. The strength of the isovector dipole-dipole interaction has been chosen to be chi = 500/A(5/3)MeV . f m(-2). Theoretical calculations show that in addition to the M1 excitations, there is considerable amount of E1 transitions especially between 2.63 MeV, which gives remarkable contribution to the fragmentation in the low-energy region of the dipole spectrum. Thus, the agreement between theory and experiment in terms of the fragmentation increases. Furthermore, the photon-absorption cross-sections in the Pigmy Dipole Resonance (PDR) region below the neutron separation energy (S-n) is compatible with experimental data.