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Description
Study of bulk properties of nuclear matter in general, and of the fission-fragment mass distribution (FFMD) in particular, is important for understanding of nuclear abundances in astrophysical processes. More specifically, the structure and composition of the FFMD is relevant for the description of abundances of elements within the 110$\le$A$\le$170 mass range in the neutron star merger scenarios. The latter use projection of fission properties gathered with actinides (N/Z$\sim$1.6) to nuclei with high isospin values (N/Z$\sim$2.0), i.e., to the nuclei currently inaccessible for experimental studies. Such a projection is therefore strongly model-dependent which leads to controversial results \cite{Gori}.
The spontaneous and low-energy fission of actinides is known to indicate dominance of asymmetric mass division in the measured FFMDs. This feature is understood to be due to microscopic effects in the fragments that are known to evolve along the nuclear chart \cite{First2} in the direction of lower isospin values, leading to a transition in the FFMD shape (symmetric fission for nuclei below A$\sim$226). However, fission of neutron-deficient nuclei around $^{180}$Hg (N/Z$\sim$1.25) has revealed prominent asymmetric mass division, despite the presence of strong microscopic effects (closed shells) in $^{90}$Zr (Z=40, N=50) \cite{First1,First3,sch1}. Similar studies made with $^{179}$Au, $^{178}$Pt and several Hg isotopes have further proved that the asymmetric mass split is a typical property of neutron-deficient nuclei in this region \cite{Second}.
This work deals with the multi-parameter study of fission properties of highly neutron-deficient nuclei isotones $^{176}$Os, $^{177}$Ir and $^{179}$Au ($N=100$). This exotic nuclear matter has been produced in fusion reactions of the $^{35}$Cl beam with the $^{144}$Sm, $^{142}$Nd and $^{141}$Pr targets. The experiment was conducted at the Advanced Science Research Center (ASRC) of the Japanese Atomic Energy Agency (JAEA). The simultaneous measurement of the FFs, neutrons and gamma-rays was done for the three used targets and at different beam energy thus leading to different excitation energy of the compound nucleus (CN).
Results on FFMD and Total Kinetic Energy (TKE) distribution will be addressed, from the point of view of fission modes coexistence, as well as their evolution with the excitation energy and isospin of the CN, all that in comparison with the Langevin calculations.
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\bibitem{Gori} S.~Goriely {\it et al.}, Phys.\ Lett.\ Phys. {\bf111}, 242502 (2013).
\bibitem{First2} A.~Andreyev {\it et al.}, Rep.\ Prog.\ Phys. {\bf81(1)}, 016301 (2017).
\bibitem{First1} A.~Andreyev {\it et al.}, Phys.\ Rev.\ Lett. {\bf105(25)}, 252502 (2010).
\bibitem{First3} K.~Nishio {\it et al.}, Phys.\ Lett.\ B {\bf748}, 89-94 (2015).
\bibitem{sch1} C. Schmit {\it et al.}, Phys.\ Rev.\ C {\bf126}, 132502 (2021).
\bibitem{Second} I.~Tsekhanovich {\it et al.}, Phys.\ Lett.\ B {\bf790}, 583-588 (2019).
\end{thebibliography}
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