  New polarization potentials have been determined based on: 1) the latest
photo-neutron cross section evaluation and a missing factor of two in previous
work, and 2) the mass dependency of the symmetry energy, $a_{sym}(A)$. The
magnitude of the first one is 35\% stronger than the currently accepted
polarization potential. The second one opens up the possibility for a
parameter-free polarization potential. Both polarization potentials are
essentially the same for heavy nuclei. The polarization effect on quadrupole
collectivity is more substantial than previously assumed for light nuclei.
Particular cases are discussed where long-standing discrepancies between
high-precision Coulomb-excitation and lifetime measurements still remain. A
solution to the long-standing discrepancy between $B(E2; 0^+_1\rightarrow
2^+_1)$ values determined in $^{18}$O by several Coulomb-excitation studies and
a high-precision lifetime measurement is provided in favor of the latter.
Polarization effects in light nuclei also influence the determination of
spectroscopic quadrupole moments in Coulomb-excitation measurements. The
hindrance of polarizability observed in the photo-neutron cross section for
single-closed shell nuclei is calculated to have a negligible effect on
quadrupole collectivity, within the existing experimental uncertainties.
