Abstract
The electric-dipole response of is investigated using the fully consistent relativistic quasiparticle random phase approximation. By analyzing the isospin structure of the response, it is shown that the low-energy (pygmy) strength separates into two segments with different isospin character. The more pronounced pygmy structure at lower energy is composed of predominantly isoscalar states with surface-peaked transition densities. At somewhat higher energy the calculated strength is primarily of isovector character, as expected for the low-energy tail of the giant dipole resonance. The results are in qualitative agreement with those obtained in recent (, ) and (, ) experiments, and provide a simple explanation for the splitting of low-energy strength into two groups of states with different isospin structure and radial dependence of the corresponding transition densities.
- Received 14 April 2009
DOI:https://doi.org/10.1103/PhysRevLett.103.032502
©2009 American Physical Society