Time scales and mechanisms of breakup influencing fusion
M. Dasgupta 1*
1 Australian National University
Understanding the interactions of weakly bound nuclei [1-3] is one of the current challenges in nuclear reactions studies. Experiments have conclusively shown that breakup and transfer processes are very significant for such nuclei, and that complete fusion is suppressed at energies above the barrier (compared to expectations for well bound nuclei). However, a quantitative understanding of the mechanism of breakup and its relationship with near-barrier fusion is still elusive. Measurements of breakup of 6,7Li and 9Be at energies below the barrier, where there is no significant capture of the fragments, have recently been completed at the Australian National University [4,5]. Coincidence measurements over a large angular range have provided a complete picture of the physical mechanisms triggering breakup [4,5]. Crucially, the measurements identify those breakup processes that are fast enough (~10−22 s) to affect fusion. The majority of these prompt breakup events are triggered by transfer of a neutron from 6Li, 9Be, and of a proton to 7Li. These mechanisms, rather than breakup following direct projectile excitation, are responsible [5,6] for the majority of the ~30% suppression of complete fusion at above-barrier energies, observed in collisions of 6,7Li and 9Be with heavy targets [7,8]. The dominance of breakup following transfer demonstrates that the reaction outcomes involving weakly bound nuclei depend not only on the properties of the two colliding nuclei, but also on the ground-state and excited state properties of their neighbours. This is a key insight for understanding and predicting reactions of weakly-bound nuclei near the limits of nuclear existence. This talk will discuss these advances towards obtaining a full picture of the reaction dynamics of weakly bound nuclei.
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