Core polarization charges of quadrupole transitions in neutron drip line nuclei

Core polarization charges of quadrupole transitions in light neutron drip line nuclei are studied by using a particle-vibration coupling model with Hartree-Fock single-particle wave functions and random phase approximation response functions in ${}_{}{}^{28}{}_{}{}^{}\mathrm{O}$. We obtain very small core polarization charges, ${\mathit{e}}_{\mathrm{pol}}$(IS)=0.14 and ${\mathit{e}}_{\mathrm{pol}}$(IV)=0.06. In addition to the smallness expected in general for light very-neutron-rich nuclei, a considerable amount of further reduction on the ${\mathit{e}}_{\mathrm{pol}}$ values arises from the cancellation between the contributions of low-energy threshold strength and those of giant resonances. It depends crucially on both the property of the one-particle multipole operator and the shell structure around the Fermi level whether the very-low-lying threshold strength contributes to the polarization charges of a given multipole constructively or destructively. © 1996 The American Physical Society.