The fusion of ${}^6\mathrm{He}$ with ${}^{206}\mathrm{Pb}$ has been studied at energies close to and below the Coulomb barrier. The experiment was carried out at the Dubna Radioactive Ion Beams complex of FLNR, JINR. The ${}^6\mathrm{He}$ beam intensity was about $5\times {10}^6\mathrm{pps}$, the maximum energy being $60.3\pm 0.4\mathrm{MeV}$. The yield of the ${}^{210}\mathrm{Po}$ isotope, produced in the $2n$-evaporation channel, demonstrates an extremely large enhancement of the sub-barrier fusion cross section as compared with the ${}^4\mathrm{He}+{}^{208}\mathrm{Pb}$ reaction. This enhancement is most likely due to the mechanism of “sequential fusion” with an intermediate neutron transfer from ${}^6\mathrm{He}$ to the Pb nucleus with positive $Q$ values.

• Received 13 January 2006

DOI:https://doi.org/10.1103/PhysRevLett.96.162701