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

The 9Be +209Bi fusion cross sections were measured in the range 37.5 MeV ≤ E lab ≤ 45.0 MeV at the Munich Tandem via the observation of ground state α-decay of the evaporation residues. Fusion cross sections of 209Bi with the “halo”11Be 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 11Be cross sections are larger than the 9Be ones in agreement with theoretical predictions based on the larger 11Be 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.