Probing the influence of weak channels on fusion dynamics in Si 28 + Ce 140 , 142

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Background: The dynamics of sub-barrier fusion between two heavy nuclei can be comprehended to a great extent within the coupled-channels formalism. However, the role of nucleon transfer channels on fusion remains ambiguous.Purpose: This work aims to address some of the open questions about the influence of neutron transfer on fusion, e.g., relative importance of inelastic excitations and neutron transfer channels, role of deformation of the nuclei in the intermediate partition, number of positive $Q$-value neutron transfer channels which may affect the fusion dynamics, etc.Method: Fusion excitation functions were measured for the systems $^{28}\mathrm{Si}+^{140,142}\mathrm{Ce}$ around the interaction barrier. The barrier height distributions were derived by the conventional double-differential recipe and a Gaussian-analytic method. Theoretical investigations by two different approaches were carried out to unravel the effects of positive $Q$-value neutron transfer channels on fusion dynamics.Results: Enhancement of sub-barrier fusion cross sections for $^{28}\mathrm{Si}+^{140}\mathrm{Ce}$, with two positive $Q$-value neutron pickup channels, is quite well reproduced by the theory. A marginal influence of neutron transfer on fusion is observed. Reasonably good reproduction of the barrier distribution is achieved for this system. In contrast, the measured excitation function for $^{28}\mathrm{Si}+^{142}\mathrm{Ce}$, with six positive $Q$-value neutron pickup channels, is not adequately accounted for within the coupled-channels framework, though the semiempirical coupled-channels model offers a better agreement with the experimental data. Nevertheless, the barrier distribution for this system cannot be satisfactorily reproduced by either model.Conclusions: A much stronger influence of neutron transfer channels is inferred in $^{28}\mathrm{Si}+^{142}\mathrm{Ce}$ compared to $^{28}\mathrm{Si}+^{140}\mathrm{Ce}$. Mismatch between experimental results and theoretical predictions in case of $^{28}\mathrm{Si}+^{142}\mathrm{Ce}$ points to the limitations of existing coupled-channels approaches to interpret the influence of neutron transfer channels on fusion dynamics comprehensively.

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