Isotopic effects in sub-barrier fusion of Si + Si systems

Recent measurements of fusion cross sections for the ²⁸Si + ²⁸Si system revealed a rather unsystematic behavior; i.e., they drop faster near the barrier than at lower energies. This was tentatively attributed to the large oblate deformation of ²⁸Si because coupled-channels (CC) calculations largely underestimate the ²⁸Si + ²⁸Si cross sections at low energies, unless a weak imaginary potential is applied, probably simulating the deformation. ³⁰Si has no permanent deformation and its low-energy excitations are of a vibrational nature. Here, previous measurements of this system reached only 4 mb, which is not sufficient to obtain information on effects that should show up at lower energies.