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Excitation energy dependence of fragment-mass distributions from fission of $$^{180,190}$$Hg formed in fusion reactions of $$^{36}$$Ar + $$^{144,154}$$Sm

Nishio, Katsuhisa; Andreyev, A. N.*; Chapman, R.*; Derkx, X.*; D$"u$llmann, C. E.*; Ghys, L.*; He${ss}$berger, F. P.*; Hirose, Kentaro; Ikezoe, Hiroshi*; Khuyagbaatar, J.*; Kindler, B.*; Lommel, B.*; Makii, Hiroyuki; Nishinaka, Ichiro; Otsuki, Tsutomu*; Pain, S. D.*; Sagaidak, R.*; Tsekhanovich, I.*; Venhart, M.*; Wakabayashi, Yasuo*; Yan, S.*

Mass distributions of fission fragments from the compound nuclei $$^{180}$$Hg and $$^{190}$$Hg formed in fusion reactions $$^{36}$$Ar+$$^{144}$$Sm and $$^{36}$$Ar+$$^{154}$$Sm, respectively, were measured at initial excitation energies of $$E^*$$($$^{180}$$Hg)=,33$$-$$66 MeV and $$E^*$$($$^{190}$$Hg)=,48$$-$$71 MeV. In the fission of $$^{180}$$Hg, the mass spectra were well reproduced by assuming only an asymmetric-mass division, with most probable light and heavy fragment masses $$bar{A}_{rm L}$$/$$bar{A}_{rm H}=$$79$$/$$101. The mass asymmetry for $$^{180}$$Hg agrees well with that obtained in the low-energy $$beta^textrm{+}$$/EC-delayed fission of $$^{180}$$Tl, from our earlier ISOLDE(CERN) experiment. Fission of $$^{190}$$Hg is found to proceed in a similar way, delivering the mass asymmetry of $$bar{A}_{rm L}$$/$$bar{A}_{rm H}=$$83$$/$$107, throughout the measured excitation energy range. The persistence as a function of excitation energy of the mass-asymmetric fission for both proton-rich Hg isotopes gives strong evidence for the survival of microscopic effects up to effective excitation energies of compound nuclei as high as 40,MeV. This behavior is different from fission of actinide nuclei and heavier mercury isotope $$^{198}$$Hg.

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