Octupole strength of β-stable and drip-line nuclei

The octupole excitations of β-stable nucleus ₈₂²⁰⁸ Pb₁₂₆, a neutron skin nucleus₂₀⁶⁰Ca₄₀ and a drip-line nucleus ₈²⁸O₂₀ are studied by using the self-consistent Hartree-Fock calculation plus the random phase approximation (RPA) with Skyrme interaction. The lowest isoscalar (IS) excitation below threshold for nuclei ₈₂²⁰⁸Pb₁₂₆ and ₂₀⁶⁰Ca₄₀, and the IS and isovector (IV) giant resonances of nuclei ₈₂²⁰⁸Pb₁₂₆, ₂₀⁶⁰ and ₈²⁸O₂₀ can be well described by collective model. For skin nucleus ₂₀⁶⁰Ca₄₀ and drip-line nucleus ₈²⁸O₂₀ the low-lying unperturbed neutron octupole strength (δN = 1) of transitions to non-resonant states are nearly unaffected and the transitions to bound states are absorbed into collective states by taking into account the RPA correlation.