Background: The fission character changes along the mercury isotopic chain, from asymmetric (${}^{180}\mathrm{Hg}$) through slightly asymmetric (${}^{190}\mathrm{Hg}$) to symmetric (${}^{198}\mathrm{Hg}$). Mercury isotopes have been studied using various techniques including $\beta$-delayed fission, Coulomb-induced fission, and fusion-fission, but the isotope ${}^{194}\mathrm{Hg}$ has not been investigated until now.

Purpose: To experimentally study the fusion-fission reaction of ${}^{194}\mathrm{Hg}$ at moderate excitation energy and to determine previously unknown independent fission yields and properties of emitted neutrons and $\gamma$ rays.

Method: The compound nucleus was formed in the reaction ${}^{12}\mathrm{C} +{}^{182}\mathrm{W}$. Prompt gamma rays emitted during the reaction were measured with the $\nu$-ball2 spectrometer. Independent fission yields of even-even nuclei were determined by detecting gamma-gamma cascades in the fission fragments and performing a maximum-likelihood analysis. The number of emitted neutrons was determined from the fragment distribution, as well as from the study of fission partners. Average momentum carried by the $\gamma$ rays was determined by the Manchester method. Additionally, the long-term $\beta$ activity of fragment residues was measured as a complementary method.

Results: The measured fission-fragment mass distribution is consistent with that of neighboring mercury isotopes, confirming the gradual change along the isotopic chain and influence of the $Z=36$ deformed proton shell in the light fragment. The independent fragment yield and distribution of fission partners is well described by the GEF model. However, there are discrepancies concerning the angular momentum of the fragments and the width of the mass distribution, confirmed by the independent residual activity measurements.

Conclusions: Our results demonstrate that the method based on fusion-fission and $\gamma$ spectroscopy is a valuable alternative to direct mass or charge measurements. Independent fission yields, correlation of fission partners, and the study of angular momentum of fragments open the possibility of a comprehensive description of the process. This is important both from a theoretical and experimental point of view and is needed to achieve further refinement of our understanding of the fission process.

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• Fission
• Low & intermediate energy heavy-ion reactions
• Nuclear fusion
• Nuclear reactions
• 190 ≤ A ≤ 219
• Gamma ray spectroscopy