Fusion around the barrier in ^11,9Be +²⁰⁹Bi

The Be-9 + Bi-209 fusion cross sections were measured in the range 37.5 MeV less than or equal to E-lab less than or equal to 45.0 MeV at the Munich Tandem via the observation of ground state alpha-decay of the evaporation residues. Fusion cross sections of Bi-209 with the "halo" Be-11 unstable projectile in the region around the Coulomb barrier were deduced from an experiment done with the same technique at the RIKEN Ring Cyclotron. Above the Coulomb barrier the Be-11 cross sections are larger than the Be-9 ones in agreement with theoretical predictions based on the larger Be-11 halo radius. Also below the barrier these theories foresee the same behavior in disagreement with the experimental results, since the two cross sections are rather similar.