Does the alpha cluster structure in light nuclei persist through the fusion process?

TL;DR

This study investigates whether alpha cluster structures in light nuclei persist during fusion, revealing that coupling between pre-existing alpha clusters and collision dynamics influences alpha emission cross-sections.

Contribution

It provides experimental evidence linking alpha cluster structures to fusion dynamics and highlights the importance of center-of-mass energy in alpha emission cross-sections.

Findings

Alpha spectra and angular distributions match statistical models

Measured alpha cross-section exceeds model predictions

Alpha cross-section depends on center-of-mass energy rather than excitation energy

Abstract

[Background] Despite the importance of light-ion fusion in nucleosynthesis, a limited amount of data exists regarding the de-excitation following fusion for such systems. [Purpose] To explore the characteristics of alpha emission associated with the decay of light fused systems at low excitation energy. [Method] Alpha particles were detected in coincidence with evaporation residues (ER) formed by the fusion of 18O and 12C nuclei. Both alpha particles and ERs were identified on the basis of their energy and time-of-flight. ERs were characterized by their energy spectra and angular distributions while the alpha particles were characterized by their energy spectra, angular distributions, and cross-sections. [Results] While the energy spectra and angular distributions for the alpha particles are well reproduced by statistical model codes, the measured cross-section is substantially underpredicted by the models. Comparison with similar systems reveals that the fundamental quantity for the alpha cross-section is Ec.m. and not the excitation energy of the fused system. [Conclusion]The enhancement in the measured alpha cross-section as compared to the statistical model codes and its dependence with Ec.m. suggest that a coupling between pre-existing alpha cluster structure and the collision dynamics is responsible for the observed alpha cross-section.