Speaker
Description
The giant dipole resonance (GDR) serves as a primary probe for investigating collective excitations and structural evolution in nuclei. In the actinide region, particularly for Thorium and Neptunium isotopes, the resonance structure is significantly influenced by large quadrupole deformation combined with strong pairing correlations, leading to a complex broadening and splitting of the $E1$ strength. In this work, we investigate $E1$ strength distributions and photo-absorption cross-sections using linear response theory (LRT), a microscopic random phase approximation (RPA) based framework implemented within a deformed Woods-Saxon basis. This approach enables a detailed decomposition of dipole modes along the principal axes of these heavily deformed systems.
Our calculations accurately describe the characteristic double-hump structure of the GDR, where the energy splitting serves as a direct signature of the underlying nuclear shape. Furthermore, we examine the emergence of $E1$ strength at sub-resonance energies. This low-energy enhancement, often associated with the pygmy dipole resonance (PDR), is examined within our microscopic approach to determine its sensitivity to the neutron-to-proton ratio and underlying shell structure in actinides. The resulting strength distributions are compared with time-dependent Hartree-Fock (TDHF) calculations and available experimental benchmarks. This comparative analysis allows us to evaluate the performance of the LRT approach and provides insights into the collective excitation characteristic of these actinide isotopes.