Background: Dynamical effects associated with the fusion of mass-symmetric systems remain a central topic of research in nuclear reaction studies. Over the past few decades, measurements of light-particle evaporation spectra and their deviations from standard statistical model predictions have been extensively employed to investigate these effects. Such indirect probes have indicated the presence of fusion hindrance, attributed to the non-fusion of higher angular momentum ($l$) states in fusion of symmetric systems. Further, more recent investigations have suggested that similar effects may also manifest in asymmetric systems particularly at higher values of excitation energies. Since the suppression of fusion at higher angular momenta suggests a corresponding reduction in the fusion cross sections for such systems, the measurement of fusion cross sections or spin distributions would give better insight into the possible fusion hindrance. However, such anomalies have not yet been explored using these probes.

Purpose: Fusion cross sections have been used as a probe to investigate the influence of entrance-channel mass asymmetry on fusion dynamics, as well as to examine the possible suppression of fusion for higher angular momentum and the deviations of light-particle evaporation spectra from the standard statistical model predictions.

Method: Evaporation-residue (ER) excitation function measurements have been carried out for the reactions ${}^{16}\mathrm{O}+{}^{64}\mathrm{Zn}$ and ${}^{32}\mathrm{S}+{}^{48}\mathrm{Ti}$, both leading to the formation of the ${}^{80}\mathrm{Sr}$ compound nucleus. The experiments were performed using the Heavy Ion Reaction Analyzer spectrometer. The experimentally obtained fusion cross sections were compared with each other as well as with the predictions from time-dependent Hartree-Fock (TDHF) calculations. Furthermore, the measured fusion cross sections have been employed to interpret the light-particle evaporation spectra for these systems, as reported in the literature.

Results: The experimentally obtained fusion cross sections for both systems show good agreement with each other on a reduced scale, and the measured data are reasonably well reproduced by TDHF calculations. The present investigation rules out the possibility of non-fusion of higher angular momentum ($l$) states in symmetric systems, contrary to earlier reports in the literature. However, the fusion timescales extracted from the TDHF calculations indicate a delay in the fusion process for both symmetric and asymmetric systems, suggesting the presence of dynamical effects.

Conclusions: The measured ER cross sections in the spanned energy region are insensitive to dynamical effects. However, the delay in the fusion timescales as predicted by TDHF calculations indicates a possible existence of fusion hindrance. To explore the fusion hindrance for such systems, it may be important to measure the spin distribution of the populated compound nucleus at high excitation energies.

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• Low & intermediate energy heavy-ion reactions
• Nuclear fusion
• Nuclear reactions
• Statistical phenomena & chaos