Fusion of ⁴⁰Ca + ^90,92,94,96Zr combinations in near and sub-barrier domains

The coupled channel model and the energy-dependent Woods–Saxon potential (EDWSP) model are applied to address the anomalies of transfer and/or collective surface excitations of the interacting nuclei in the fusion of ⁴⁰Ca with ^90,92,94,96Zr targets. In fusion of ⁴⁰Ca + ⁹⁰Zr reaction, the phonon states such as 2⁺ and 3^- in projectile and target are found to be appropriate to account for anomalously large fusion enhancement of experimental data. For ⁴⁰Ca + ⁹²Zr reaction, the addition of neutron transfer channel along with low-lying phonon states of participant nuclei is sufficient to retrieve experimental data. Without considering two-neutron (2n) pickup channel, the coupled channel outputs are unable to recover the fusion data at below barrier area. In case of ⁴⁰Ca + ⁹⁴Zr reaction, up to four-positive Q-value neutron transfer (4n) channels and for ⁴⁰Ca + ⁹⁶Zr reaction up to six-positive Q-value neutron transfer (6n) channels are responsible for larger sub-barrier fusion enhancements for these reactions in comparison to lighter target systems. In the EDWSP method, the energy-dependent character of nuclear potential reduces original interaction barrier by dynamically altering the characteristics of the interaction barrier and hence introduces gross potential modifications in the tunneling regions. This energy dependency also produces shallow potential pocket of the EDWSP fusion barrier at lowest incident energies, which can be connected with the Pauli repulsion effects. Thus, model outputs predict larger fusion cross sections relative to computations based on one-dimensional barrier penetration model (BPM), and hence, EDWSP computations are reliable to gain close agreement with the experimental data for the present reactions. (author)