Background: Complete fusion cross sections in collisions of light, weakly bound nuclei and high Z targets show suppression of complete fusion at above-barrier energies. This has been interpreted as resulting from breakup of the weakly bound nucleus prior to reaching the fusion barrier, reducing the probability of complete charge capture. Below-barrier studies of reactions of 9 Be have found that breakup of 8 Be formed by neutron stripping dominates over direct breakup, and that transfer triggered breakup may account for the observed suppression of complete fusion.Purpose: This paper investigates how the above conclusions are affected by lifetimes of the resonant states that are populated prior to breakup. If the mean life of a populated resonance (above the breakup threshold) is much longer than the fusion timescale, then its breakup (decay) cannot suppress complete fusion. For shortlived resonances, the situation is more complex. This work explicitly includes the mean life of the short-lived 2 + resonance in 8 Be in classical dynamical model calculations to determine its effect on energy and angular correlations of the breakup fragments and on model predictions of suppression of cross sections for complete fusion at above-barrier energies.Method: Previously performed coincidence measurements of breakup fragments produced in reactions of 9 Be with 144 Sm, 168 Er, 186 W, 196 Pt, 208 Pb and 209 Bi at energies below the barrier have been re-analysed using an improved efficiency determination of the BALiN detector array. Predictions of breakup observables and of complete and incomplete fusion at energies above the fusion barrier are then made using the classical dynamical simulation code PLATYPUS, modified to include the effect of lifetimes of resonant states.Results: The agreement of the breakup observables is much improved when lifetime effects are included explicitly. Sensitivity to sub-zeptosecond lifetime is observed. The predicted suppression of complete fusion due to breakup is nearly independent of Z, and has an average value of ∼ 9%. This is below the experimentally determined fusion suppression which is typically ∼ 30% in these systems.Conclusions: Inclusion of resonance lifetimes is essential to correctly reproduce breakup observables. This results in a larger fraction of nuclei remaining intact at the fusion barrier radius, compared with calculations that do not explicitly include lifetime effects. The more realistic treatment of breakup followed in this work leads to the conclusion that the suppression of complete fusion cannot be fully explained by breakup prior to reaching the fusion barrier. Only one third of the observed fusion suppression can be attributed to the competing process of breakup. Other mechanisms that can suppress complete fusion must therefore be investigated. One of the possible candidates in cluster transfer that produces the same heavy target-like nuclei as those formed by incomplete fusion. PACS numbers: 25.40.Hs,25.70.Hi,25.70.Pq,25.70.Ef It was recognised early on [11] that ver...

Background: At above-barrier energies, complete fusion cross sections in collisions of light weakly bound nuclei with heavy target nuclei are suppressed when compared to well-bound nuclei. Breakup of the projectilelike nucleus was proposed to be the cause. In addition to direct breakup, breakup following transfer was shown to be substantial. Purpose: We investigate breakup in reactions with 7 Li, triggered by sub-barrier proton pickup to unbound states in 8 Be, which subsequently separate into two α particles. Method: Measurements of sub-barrier disintegration of 7 Li on a 58 Ni target were made using the Heavy Ion Accelerator Facility at the Australian National University. Combining the experimental results with classical simulations of post-breakup acceleration, we study the sensitivity of α-α energy and angle correlations to the proximity of disintegration to the target (proton donor) nucleus. Results: The simulations indicate that disintegration as the colliding nuclei approach each other leads to large angular separations θ 12 of the α fragments. The detectors allow for a maximum opening angle of θ 12 = 132 • , such that the present experiment is largely insensitive to breakup occurring when the collision partners approach each other. The data are consistent with disintegration of (a) the 0 + 8 Be ground state far from the targetlike nucleus, and (b) the 2 + 8 Be resonance near the targetlike nucleus when the 8 Be is receding from the targetlike nucleus. Conclusions: The present results shed light on the near-target component of transfer-induced breakup reactions. The distribution of events with respect to the opening angle of the α particles, and the orientation of their relative velocity with respect to the velocity of their center of mass, gives insights into their proximity to the target at the moment of breakup. Further measurements with larger angular coverage and more complete simulations are required to fully understand the influence of breakup on fusion.

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In collisions of light, stable, weakly bound nuclides, complete fusion (capture of all of the projectile charge) has been found to be suppressed by ∼30% at above-barrier energies. This is thought to be related to their low thresholds for breakup into charged clusters. The observation of fusion suppression in the neutron-rich radioactive nucleus 8 Li is therefore puzzling: the lowest breakup threshold yields 7 Li + n which cannot contribute to fusion suppression because 7 Li retains all the projectile charge. In this work, the full characteristics of 8 Li breakup in reactions with 209 Bi are presented, including, for the first time, coincidence measurements of breakup into charged clusters. Correlations of cluster fragments show that most breakup occurs too slowly to significantly suppress fusion. However, a large cross section for unaccompanied α particles was found, suggesting that charge clustering, facilitating partial charge capture, rather than weak binding is the crucial factor in fusion suppression, which may therefore persist in exotic nuclides.