  Measurement of the energy dependence of the fusion cross-sec on at
sub-barrier energies provides an important test for theoretical models of
fusion. To extend the measurement of fusion cross-sections in the sub-barrier
domain for the 18O+12C system. Use the new experimental data to confront
microscopic calculations of fusion. Evaporation residues produced in fusion of
18O ions with 12C target nuclei were detected with good geometric efficiency
and identified by measuring their energy and time-of-flight. Theoretical
calculations with a density constrained time dependent Hartree-Fock (DC-TDHF)
theory include for the first time the effect of pairing on the fusion
cross-section. Comparison of the measured fusion excitation function with the
predictions of the DC-TDHF calculations reveal that the experimental data
exhibits a smaller decrease in cross-section with decreasing energy than is
theoretically predicted. The larger cross-sections observed at the lowest
energies measured indicate a larger tunneling probability for the fusion
process. This larger probability can be associated with a smaller, narrower
fusion barrier than presently included in the theoretical calculations.
