$N/Z$ dependence of core polarization charges for electric quadrupole transitions is studied in C isotopes by using a microscopic particle-vibration model in which Hartree-Fock and random-phase approximations are used to calculate the single-particle wave functions and giant quadrupole resonances. A large quenching of the polarization charges is found in nuclei with a large $N/Z$ ratio. Recent experimental data of quadrupole moments of ${}^{15}\mathrm{B}$ and ${}^{17}\mathrm{B}$ are reproduced well by using the calculated polarization charges for shell-model wave functions.

• Received 26 December 2000

DOI:https://doi.org/10.1103/PhysRevC.63.064310