Angular momentum and cross sections for fusion with weakly bound nuclei: breakup, a coherent effect

Lithium–lithium fusion evaporation research

In this study we have explored 6Li + 7Li fusion evaporation reactions cross sections dependencies on both nuclear level density and various spin combination effects. The reaction cross section was calculated in the energy range of 0.1–16 MeV projectile of 6Li on the fixed target of 7Li. The excited compound nucleus (13C) can decay into various channels, and its decay rate in any given channel is proportional to the available phase space, i.e., the corresponding level density of it which is explained in the present study. In the present study, LISE++, PACE4, NRV and GEMINI codes were used to determine cross section of evaporation residues cross sections of 13C.

Unraveling the Reaction Mechanisms Leading to Partial Fusion of Weakly Bound Nuclei

Collisions between complex nuclei may give rise to their total or partial fusion. The latter case is found experimentally to gain importance when one of the colliding nuclei is weakly bound. It has been commonly assumed that the partial fusion mechanism is a two-step process, whose first step is the dissociation of the weakly bound nucleus, followed by the capture of one of the fragments. To assess this interpretation, we present the first implementation of the three-body model of inclusive breakup proposed in the 1980s by Austern et al. [Phys. Rep. 154, 125 (1987)PRPLCM0370-157310.1016/0370-1573(87)90094-9] that accounts for both the direct, one-step, partial fusion and the two-step mechanism proceeding via the projectile continuum states. Contrary to the widely assumed picture, we find that, at least for the investigated cases, the partial fusion is largely dominated by the direct capture from the projectile ground state.

Puzzle of Complete Fusion Suppression in Weakly Bound Nuclei: A Trojan Horse Effect?

Experimental studies of nuclear collisions involving light weakly bound nuclei show a systematic suppression of the complete fusion cross section by ∼30% with respect to the expectation for tightly bound nuclei, at energies above the Coulomb barrier. Although it is widely accepted that the phenomenon is related to the weak binding of these nuclei, the origin of this suppression is not fully understood. Here, we present a novel approach that provides the complete fusion for weakly bound nuclei and relates its suppression to the competition between the different mechanisms contributing to the reaction cross section. The method is applied to the ^{6,7}Li+^{209}Bi reactions, where we find that the suppression of complete fusion is mostly caused by the flux associated with nonelastic breakup modes, such as the partial capture of the projectile (incomplete fusion), whereas the elastic breakup mode is found to play a minor role. Finally, we demonstrate that the large α yields observed in these reactions can be naturally explained as a consequence of a Trojan Horse mechanism.

Exploring fusion at extreme sub-barrier energies with weakly bound nuclei

Results of measurement of residues formed in fusion of (6)Li with (198)Pt in the energy range of 0.68 < E/V(b) < 1.3 using a new sensitive off-beam technique are reported. The fusion excitation function and the derived average angular momenta do not indicate a change of slope at deep sub-barrier energies, contrary to recent observations. The present results for a system with weakly bound projectile confront the current understanding of the fusion hindrance at these low energies, underlying the role of internal reorganization on the dynamical path towards fusion.