209Bi(6He,α) reaction mechanisms studied near the Coulomb barrier using n–α coincidence measurements

The 6He+209Bi reaction displays a remarkably large cross section for α-particle emission at energies near the Coulomb barrier. The possible reactions that may produce the observed α particles include two-neutron transfer, one-neutron transfer, and direct projectile breakup. Each of these mechanisms results in a distinctive angular correlation between the α particle and outgoing neutron(s). A neutron-α-particle coincidence experiment was performed to separate these different modes. The neutron data show significant angular correlations. Monte Carlo simulations of one-neutron transfer are compared with the experimental data. It is shown that approximately 20% of the observed α-particle yield is due to this process.