Modelling incomplete fusion dynamics of weakly-bound nuclei at near-barrier energies

The classical dynamical model for reactions induced by weakly-bound nuclei at near-barrier energies is developed further. It allows a quantitative study of the role and importance of incomplete fusion dynamics in asymptotic observables, such as the population of high-spin states in reaction products as well as the angular distribution of direct alpha-production. Model calculations indicate that incomplete fusion is an effective mechanism for populating high-spin states, and its contribution to the direct alpha production yield diminishes with decreasing energy towards the Coulomb barrier. It also becomes notably separated in angles from the contribution of no-capture breakup events. This should facilitate the experimental disentanglement of these competing reaction processes.Comment: 12 pages, 7 figures (for better resolution figures please contact the author), Accepted in Journal of Physics

Effects of nuclear molecular configurations on the astrophysical S-factor for 16^{16}O + 16^{16}O

The impact of nuclear molecular configurations on the astrophysical S-factor for $^{16}$O + $^{16}$O 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.Comment: In press in Physics Letters

How does breakup influence the total fusion of 6,7^{6,7}Li at the Coulomb barrier?

Total (complete + incomplete) fusion excitation functions of $^{6,7}$Li on $^{59}$Co and $^{209}$Bi targets around the Coulomb barrier are obtained using a new continuum discretized coupled channel (CDCC) method of calculating fusion. The relative importance of breakup and bound-state structure effects on total fusion is particularly investigated. The effect of breakup on fusion can be observed in the total fusion excitation function. The breakup enhances the total fusion at energies just around the barrier, whereas it hardly affects the total fusion at energies well above the barrier. The difference between the experimental total fusion cross sections for $^{6,7}$Li on $^{59}$Co is notably caused by breakup, but this is not the case for the $^{209}$Bi target.Comment: 9 pages, 9 figures, Submitted to Phys. Rev.

Near-barrier Fusion Induced by Stable Weakly Bound and Exotic Halo Light Nuclei

The effect of breakup is investigated for the medium weight $^{6}$Li+$^{59}$Co 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 to $^{6}$He+$^{59}$Co a reaction induced by the borromean halo nucleus $^{6}$He.Comment: 6 pages, 3 figures. A talk given at the FUSION06: International Conference on Reaction Mechanisms and Nuclear Structure at the Coulomb barrier, March 19-23, 2006, San Servolo, Venezia, Ital

Cluster Model for Near-barrier Fusion Induced by Weakly Bound and Halo Nuclei

The influence on the fusion process of coupling transfer/breakup channels is investigated for the medium weight $^{6,7}$Li+$^{59}$Co systems in the vicinity of the Coulomb barrier. Coupling effects are discussed within a comparison of predictions of the Continuum Discretized Coupled-Channels model. Applications to $^{6}$He+$^{59}$Co induced by the borromean halo nucleus $^{6}$He are also proposed.Comment: 5 pages, 3 figures, FINUSTAR2 Conference, Aghios Nikolaus, Crete, Greece. 10-14 September 200

Relating breakup and incomplete fusion of weakly-bound nuclei through a classical trajectory model with stochastic breakup

A classical dynamical model that treats break-up stochastically is presented for low energy reactions of weakly-bound nuclei. The three-dimensional model allows a consistent calculation of breakup, incomplete and complete fusion cross sections. The model is assessed by comparing the breakup observables with CDCC quantum mechanical predictions, which are found to be in reasonable agreement. Through the model, it is demonstrated that the breakup probability of the projectile as a function of its distance from the target is of primary importance for understanding complete and incomplete fusion at energies near the Coulomb barrier.Comment: Accepted in Physical Review Letter

Alpha particle production by molecular single-particle effect in reactions of 9^{9}Be just above the Coulomb barrier

The $\alpha$-particle production in the dissociation of $^{9}$Be on $^{209}$Bi and $^{64}$Zn at energies just above the Coulomb barrier is studied within the two-center shell model approach. The dissociation of $^{9}$Be on $^{209}$Bi is caused by a molecular single-particle effect (Landau-Zener mechanism) before the nuclei reach the Coulomb barrier. Molecular single-particle effects do not occur at that stage of the collision for $^{9}$Be+$^{64}$Zn, and this explains the absence of fusion suppression observed for this system. The polarisation of the energy level of the last neutron of $^{9}$Be and, therefore the existence of avoided crossings with that level, depends on the structure of the target.Comment: 5 pages, 4 figure

Dissipative quantum dynamics in low-energy collisions of complex nuclei

Model calculations that include the effects of irreversible, environmental couplings on top of a coupled-channels dynamical description of the collision of two complex nuclei are presented. The Liouville-von Neumann equation for the time-evolution of the density matrix of a dissipative system is solved numerically providing a consistent transition from coherent to decoherent (and dissipative) dynamics during the collision. Quantum decoherence and dissipation are clearly manifested in the model calculations. Energy dissipation, due to the irreversible decay of giant-dipole vibrational states of the colliding nuclei, is shown to result in a hindrance of quantum tunneling and fusion.Comment: Accepted in Physical Review