Effective Charge of Neutron Quasiparticle Pairs inPb206andPb204

The transition charge densities to the lowest $J^{\pi }=2^{+},4^{+}$ states in ${}_{}{}^{204,206}{}_{}{}^{}\mathrm{Pb}$ have been determined through inelastic electron scattering. Their shape is insensitive to the microscopic structure of these states, dominantly of neutron character, but it bears striking similarity to that of the low-frequency phonon of the core. This is regarded as strong evidence supporting the view that the "dressing" of these neutron excitations is mediated through core polarization with the lowest-frequency phonon acting as the most important doorway.