Background: The fission fragment mass distribution (FFMD) has been known as one of the most fascinating observables. Its exploration provides information on fragment properties that reveal multiple interesting aspects of the fission phenomenon. The curiosity of investigating the neutron-deficient sublead nuclei developed after the discovery of unexpected asymmetric fission for ${}^{180}\mathrm{Hg}$ [Andreyev et al., Phys. Rev. Lett. 105, 252502 (2010)]. Numerous experiments involving heavy-ion-induced reactions were conducted to produce a variety of neutron-deficient sublead compound nuclei to study the underlying fission dynamics. These sublead nuclei were generally found to possess flat-topped mass distributions, but the exact number of asymmetric modes involved in generating such structures is still unresolved. Moreover, the role of shell effects in forming asymmetric splits in the sublead nucleus has not yet been fully explored.

Purpose: This article presents the study of fission dynamics for ${}^{192}\mathrm{Hg}$, populated via fusion of ${}^{32}\mathrm{S}$ with ${}^{160}\mathrm{Gd}$. It illustrates the FFMDs of ${}^{192}\mathrm{Hg}$ at excitation energies ($E^{*}\mathrm{s}$) between 49.3 and 67.6 MeV. Moreover, it provides a comparative study of experimentally measured fission-fragment properties and the corresponding gef (GEneral description of Fission observables) model code outcomes.

Method: The carbon-backed ${}^{160}\mathrm{Gd}$ target was bombarded with ${}^{32}\mathrm{S}$ ions at five different laboratory energies, spanning a wide range from 134–156 MeV. Two multiwire proportional counters, each having dimensions 16 cm $\times$ 11 cm, were employed in order to derive velocity information of the fragments. Further, these velocities eventually generated the fission-fragment mass and kinetic energy distributions.

Results: For all energies, the triple-Gaussians satisfactorily fit the experimentally obtained flat-topped FFMDs. Later, the mean number of protons in the light and heavy fragments, extracted from the experimental distributions, was found to be influenced by quadrupole-deformed shell gaps at $Z \approx$ 34, 36, 42, 44, and 46. Similar observations have been made in studies of the Hg isotopic chain. Whereas, a negligible role of octopole-deformed shell gaps ($N \approx$ 52 and 56) in deciding the mean number of neutrons in fragments was registered. Contrary to this, gef predicted the mean number of neutrons in the light fragment around 52, which hinted at the role of octopole-deformed shell gaps. The present study reported the inexistence of the quasifission process. Both experimental and theoretical symmetric fission fractions (SFFs) were observed to increase with increasing $E^{*}$. Generally, the theoretically predicted SFF values were higher than the experimental values. Moreover, the comparison of SFFs for different nuclei at $E^{*} \approx$ 49 MeV indicated that SFFs tend to grow with an increasing $N/Z$ ratio.

Conclusions: The incompetence of a single-Gaussian to fit the experimental distribution verified the existence of an asymmetric fission mode component in addition to the symmetric fission component. The experimental $Z_{\mathrm{peak}}$ values were found to be influenced by the quadrupole-deformed shell gaps. The dominant role of proton shell gaps has also been observed by comparing the present results with the previously available data for a wide range of Hg isotopes. Although gef partially reproduces the experimentally derived $Z_{\mathrm{peak}}$ and $N_{\mathrm{peak}}$ values (with differences of no more than 3), it overpredicts the symmetric contributions. SFF values have been observed to increase with increasing $N/Z$ ratio.

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• Fission
• Low & intermediate energy heavy-ion reactions
• Nuclear reactions
• 190 ≤ A ≤ 219