Elastic scattering and transfer in the ${}^6\mathrm{He}{+}^{209}\mathrm{Bi}$ system below the Coulomb barrier

The interaction of ${}^6\mathrm{He}$ with ${}^{209}\mathrm{Bi}$ has been studied over a range of energies well below the nominal Coulomb barrier. A ${}^4\mathrm{He}$ group of remarkable intensity, first observed in a previous experiment at near-barrier energies, continues to dominate the reaction in the sub-barrier regime. A total cross section of nearly 200 mb was measured for this group at 6 MeV below the barrier. This very large value is shown to be consistent with the total reaction cross section deduced from a simultaneously-measured elastic scattering angular distribution.