Cluster transfer in the reaction ¹⁶O+²⁰⁸Pb and its role in understanding the suppression of fusion, M. Evers, The Australian National University, Australia − In nuclear reactions of heavy nuclei, the phenomenon of fusion suppression seen both at deep sub-barrier and at above-barrier energies has been the source of great dispute [1–4].  A consistent understanding of the mechanisms leading to this suppression of fusion is crucial for e.g. reliable predictions of reaction rates in astrophysical scenarios.  It has been argued [1, 5] that the suppression of fusion above the barrier can be associated with deep inelastic collisions (DIC), leaving the residual nuclei in highly excited states. Measurements of these DIC products [6, 7] show that both energy dissipation of kinetic energy into nucleonic degrees of freedom and nucleon transfer are important and related to each other.  We expect in reality a smooth transition from nucleon transfer to low-lying discrete states in sub-barrier quasi-elastic scattering on one end, to (multi-)nucleon transfer leading to the dissipation in DIC at energies above the barrier on the other end.  Detailed measurements of the backscattered flux in the reaction ¹⁶O+²⁰⁸ Pb, performed at the Heavy-Ion accelerator facility of the Australian National University will be presented.  They suggest that the concept of energy dissipation may play a significant role already at energies below the fusion barrier [8]. The systematic analysis to determine the transfer probabilities of the detected projectile-like fragments will be described. A detailed comparison with calculations based on the coupled reaction channels framework as well as the fully microscopic time-dependent Hartree-Fock (TDHF) model will be presented.  Results indicate that (i) the transfer of two protons (2p) occurs with probabilities ∼10% at energies near the fusion barrier, (ii) the 2p transfer probabilities are significantly enhanced compared to TDHF calculations, and (iii) 2p transfer leads to excitation energies as high as ∼13 MeV in the residual nuclei.  These results show that experimental and theoretical work on multi-nucleon transfer, particularly cluster transfer, may be a key towards developing a complete understanding of both fusion and scattering in low energy heavy-ion collisions, how these processes may be linked to the suppression of fusion at sub-barrier energies, and how processes leading to large excitation energies in the residual nuclei may be included in future nuclear reaction models.