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Coincidence measurements of breakup fragments were carried out for the 7Li+144Sm and 6,7Li+207,208Pb,209Bi reactions at sub-barrier energies. Breakup modes in reactions of 6,7Li were identified through the reaction Q values, and the time-scales of each pr

Using a back-angle detector array covering 117° to 167°, coincidence measurements of breakup fragments at sub-barrier energies have enabled the complete characterisation of the breakup processes in the reactions of 6,7Li with 208Pb. Those breakup proces

A self-contained Fortran-90 program based on a three-dimensional classical dynamical reaction model with stochastic breakup is presented, which is a useful tool for quantifying complete and incomplete fusion, and breakup in reactions induced by weakly-bound two-body projectiles near the Coulomb barrier. The code calculates (i) integrated complete and incomplete fusion cross sections and their angular momentum distribution, (ii) the excitation energy distribution of the primary incomplete-fusion products, (iii) the asymptotic angular distribution of the incomplete-fusion products and the surviving breakup fragments, and (iv) breakup observables, such as angle, kinetic energy and relative energy distributions.

The successful coupled-channels model of peripheral reactions has been widely used to model fusion. Following measurements of inhibition of fusion at deep sub-barrier energies, it has been proposed that to properly describe the nuclear fusion process, quantum decoherence and energy dissipation should be treated simultaneously with coherent quantum superpositions, the latter being the basis of the coupled-channels model. The necessity for a simultaneous inclusion of quantum coherence and decoherence is discussed, and the first implementation through a density matrix model is described.

Below-barrier no-capture breakup measurements of the weakly bound Be9 nucleus, incident on targets ranging in atomic number from 62 to 83, have been carried out using a large-area high-resolution back-angle detector array. It is shown that the three-body

The above-barrier suppression of complete fusion in reactions with weakly bound stable nuclei displays a strong correlation with their breakup threshold. Simplistically, this observation suggests that suppression of complete fusion is due to the direct breakup of the weakly bound partner, prior to reaching the barrier. However, new measurements of breakup at energies below the fusion barrier show that breakup following transfer, rather than direct breakup, is the dominant mechanism. The insights into the physical mechanisms of breakup from these measurements, in conjunction with theoretical developments, are being used to obtain an understanding of the relationship between sub-barrier breakup and suppression of complete fusion.

Mass-angle distributions carry detailed information on the characteristics of quasi- fission, and thus of the dynamics of heavy element formation reactions. Recent experimental results are presented and discussed.

The coupled channels model has generally been very successful in describing the different reaction outcomes following the collision of heavy nuclei. However, several outstanding problems remain - amongst them the inability to simultaneously describe elastic scattering and fusion data, and more recently the failure to consistently describe deep-sub barrier and above-barrier fusion. Possible reasons include deviation of the nuclear potential from the assumed Woods-Saxon form, and the emergence of processes which cannot be described within the coherent coupled channels framework. The question is whether there are inadequacies in the current models which need to be addressed before we can hope to get a consistent description of the main reaction processes. We put forward the possibility that dissipation near the fusion barrier and the consequent loss of coherence need to be considered for a realistic description of nuclear collisions.

A novel quantum dynamical model based on the dissipative quantum dynamics of open quantum systems is presented. It allows the treatment of both deep-inelastic processes and quantum tunneling (fusion) within a fully quantum mechanical coupled-channels approach. Model calculations show the transition from pure state (coherent) to mixed state (decoherent and dissipative) dynamics during a near-barrier nuclear collision. Energy dissipation, due to irreversible decay of giant-dipole excitations of the interacting nuclei, results in hindrance of quantum tunneling.

The astrophysical S-factor for 16O+16O is investigated within the adiabatic molecular picture. It very well explains the available experimental data. The collective radial mass causes a pronounced resonant structure in the S-factor excitation function, providing a motivation for measuring the 16O+16O fusion cross section at deep sub-barrier energies

Mass-angle correlations of binary fragments produced in O16+Pb204, S34+W186, and Ti48,50+Er166,170 reactions have been measured for a range of bombarding energies around their Coulomb barriers. At above-barrier energies, the width of the mass distributions for the fission-like fragments in the Ti50+Er170 reaction are found to be higher than those from the same compound system at similar excitation energies populated via the more mass asymmetric entrance channel reaction S34+W186, which in turn is higher than those for the O16+Pb204 system. The width of the mass distributions of the Ti+Er systems is found to increase with decreasing bombarding energies, in contrast with those of the O16+Pb204 and S34+W186 systems, which show a monotonic reduction in mass widths. This may be associated with the elongated contact configuration at sub-barrier energies.

Forming the same heavy compound nucleus with different isotopes of the projectile and target elements allows nuclear structure effects in the entrance channel (resulting in static deformation) and in the dinuclear system to be disentangled. Using three isotopes of Ti and W, forming 232Cm, with measurement spanning the capture barrier energies, alignment of the heavy prolate deformed nucleus is shown to be the main reason for the broadening of the mass distribution of the quasifission fragments as the beam energy is reduced. The complex, consistently evolving mass-angle correlations that are observed carry more information than the integrated mass or angular distributions, and should severely test models of quasifission.

The impact of nuclear molecular configurations on the astrophysical S-factor for 16O + 16O is investigated within the realistic two-center shell model based on Woods-Saxon potentials. These molecular effects refer to the formation of a neck between the interacting nuclei and the radial dependent collective mass parameter. It is demonstrated that the former is crucial to explain the current experimental data with high accuracy and without any free parameter, whilst in addition the latter predicts a pronounced maximum in the S-factor. In contrast to very recent results by Jiang et al., the S-factor does not decline towards extremely low values as energy decreases.

New measurements of fusion cross sections at deep sub-barrier energies for the reactions 16O+204,208Pb show a steep but almost saturated logarithmic slope, unlike 64Ni-induced reactions. Coupled channels calculations cannot simultaneously reproduce these new data and above-barrier cross-sections with the same Woods-Saxon nuclear potential. It is argued that this highlights an inadequacy of the coherent coupled channels approach. It is proposed that a new approach explicitly including gradual decoherence is needed to allow a consistent description of nuclear fusion.

The effect of breakup is investigated for the medium weight6Li+59Co system in the vicinity of the Coulomb barrier. The strong coupling of breakup/transfer channels to fusion is discussed within a comparison of predictions of the Continuum Discretized Coupled-Channels model which is also applied to6He+59Co a reaction induced by the borromean halo nucleus6He.

The incomplete fusion mechanism following breakup of Li6,7 and Be9 projectiles incident on targets of Bi209 and Pb208 is investigated through isomer ratio measurements for the At212 and Po211 products. The phenomenological analysis presented in this paper indicates that incomplete fusion brings relatively more angular momentum into the system than equivalent reactions with a direct beam of the fused fragment. This is attributed to the trajectories of breakup fragments. Calculations with a 3D classical trajectory model support this. Isomer ratio measurements for incomplete fusion reactions can provide a test of new theoretical models of breakup and fusion.

A theory of the competition between fusion and quasifission in a heavy fusing system is proposed, which is based on a master equation and the two-center shell model. Fusion and quasifission arise from a diffusion process in an ensemble of nuclear shapes