Giant resonance polarization terms in the nucleus-nucleus potential

Effective polarization potentials for adiabatic Coulomb coupling to giant resonances are derived for heavy-ion collisions. The isovector giant dipole resonance and isoscalar giant quadrupole resonance are found to contribute attractive terms varying as Z21Z22/r-4 and Z21Z22/r6 respectively to the effective nucleus-nucleus potential. Because of the strong Z-dependence these terms become significant in the collision of very heavy ions, dominating the far tail of the ion-ion potential. Analysis of a recently determined surface potential for 40Ar + 160Gd suggests the presence of such polarization terms. We calculate that for a 208Pb + 208Pb collision the adiabatic polarization potential exceeds the real nuclear ion-ion potential estimated by the proximity theorem for center-of-mass separation distances r >= 1.4(A1sup(1/3) + A2sup(1/3)). Furthermore, at the point where the polarization and nuclear potentials become equal - Vsub(pol) may be 2-3 MeV for very heavy systems. Therefore the adiabatic polarization represents a measurable effect which may be expected to play a significant role for heavy-ion reactions in which discrete final states are observed. (orig.)