Exploring the role of low-lying intrinsic degrees of freedom and their impact on fusion cross-sections

TL;DR

This study investigates how low-lying intrinsic degrees of freedom, including vibrational and rotational states, influence fusion cross-sections in specific nuclear reactions, highlighting the effects of deformation parameters on fusion dynamics.

Contribution

It provides a detailed analysis of the impact of low-lying intrinsic states and deformation effects on fusion cross-sections using coupled-channel calculations, with comparison to experimental data.

Findings

Theoretical calculations closely match experimental data for key excited states.

Hexadecapole deformation significantly influences fusion cross-sections.

Rotational levels beyond 6+ have minimal impact when positive deformation is considered.

Abstract

The present work focuses on examining the low-lying intrinsic degrees of freedom and their impact on fusion dynamics. Fusion cross-sections were calculated using the coupled-channel code CCFULL for four specific reactions: $^{18}$O+$^{74}$Ge, $^{18}$O+$^{148}$Nd, $^{18}$O+$^{182}$W, and $^{18}$O+$^{186}$W, all conducted at energies below the Coulomb barrier across various energy levels. Vibrational and rotational features were studied concerning energy to distinguish their respective effects on fusion properties. The results indicate that the theoretical calculations for the nuclei $^{74}$Ge, $^{148}$Nd, $^{182}$W and $^{186}$W closely match the experimental data, particularly for the $2^+$ excited states. While slight discrepancies are observed for other excited states ($4^+$ and $6^+$), overall agreement remains significant. Additionally, the study reveals that hexadecapole deformation with different magnitudes have significant influences on the fusion cross-section. In cases where $\beta_4$ has a positive value, rotational levels beyond $6^+$ have minimal impact on the cross-section, resulting in a notable difference in the contribution of sequential channels. In contrast, for negative $\beta_4$ values, rotational energy levels up to the $2^+$ state substantially affect the fusion characteristics. Furthermore, the analysis extends to the estimation of the relative change ($\Delta\sigma_{fus}$) between the excited states and the ground state, both with and without considering coupling terms.