  The coupled-channels technique is applied to analyze recent fusion data for
$^{48}$Ca+$^{48}$Ca. The calculations include the excitations of the low-lying
$2^+$, $3^-$ and $5^-$ states in projectile and target, and the influence of
mutual excitations as well as the two-phonon quadrupole excitations is also
investigated. The ion-ion potential is obtained by double-folding the nuclear
densities of the reacting nuclei with the M3Y+repulsion effective interaction
but a standard Woods-Saxon potential is also applied. The data exhibit a strong
hindrance at low energy compared to calculations that are based on a standard
Woods-Saxon potential but they can be reproduced quite well by applying the
M3Y+repulsion potential with an adjusted radius of the nuclear density. The
influence of the polarization of high-lying states on the extracted radius is
discussed.
