Isoscalar and neutron modes in the E 1 spectra of Ni isotopes and the relevance of shell effects and the continuum

摘要: We study theoretically the electric dipole transitions of even Ni isotopes at low energies, using self-consistent quasiparticle random-phase approximation with D1S Gogny interaction and a continuum-RPA model SLy4 Skyrme force. analyze isoscalar states, isovector polarizability. define reference value for polarizability to remove trivial dependence on mass number. compare our results data other calculations, focus collective shell effects, threshold transitions. Our support presence strong transition, little or moderate $E1$ strength, as universal feature ordinary nuclei. In moderately neutron-rich isotopes, namely $^{68}\mathrm{Ni}$ neighboring this transition is found bimodal due couplings surface neutrons. An adequate treatment continuum states appears essential describing suprathreshold especially beyond $^{68}\mathrm{Ni}$. Very exotic $(Ng50)$ are highly polarizable, practically all their strength in continuum. The neutron-skin thickness influenced by structure different ways, so they can appear anticorrelated. A comparison existing lighter (Ca) heavier (Sn) nuclei suggests that so-called pygmy strongly effects that, partly reason, its isospin depends region.