Search for possible fission modes at high excitation energies in Fm 254

Banerjee T. Kozulin E.M. Burtebayev N.T. Gikal K.B. Knyazheva G.N. Itkis I.M. Novikov K.V. Kvochkina T.N. Mukhamejanov Y.S. Pan A.N.
April 2022 American Physical Society

Physical Review C
2022 #105 Issue 4

Background: Shell effects have been found to influence both the compound nuclear fission (CNF) and quasifission processes. Besides quasifission processes, which fission modes remain active at excitation energy (E?) as high as 56 MeV should be investigated. Purpose: We investigate the signatures of fission modes in Fm254 populated by O16+U238 through the mass distribution (MD) and total kinetic energy distribution (TKED). Method: The mass-Total kinetic energy distributions (M-TKED) of fission fragments of the reaction O16+U238 have been measured at two laboratory energies Elab=89 and 101 MeV. The spontaneous fission (SF) of Fm254, one-dimensional (1D) fragment MD, and two-dimensional (2D) M-TKEDs of O16+U238 have been described by the multimodal random neck rupture (MM-RNR) model. Results: Channel probabilities and the characteristics of different fission modes are obtained and discussed in detail. The enhancement observed in the mass yield (?10-2%) in the region 60-70 u for the light fragments at E-45 MeV goes away at the higher E-56 MeV. The heavy fragments of S1 and S2 modes are found to be associated with Z?53 and Z?56 shells, respectively. The slope of asymmetric to symmetric fission yields (when plotted against E?) of O16+U238 is found to be similar to that of previously reported O18+Pb208. Conclusions: Analysis of 2D M-TKED data by the MM-RNR model reveals the possible presence of fission modes in O16+U238. The liquid-drop-like broad symmetric SL mode is found to peak at a lower energy than predicted by the Viola systematic, which matches mostly with that of Standard 2 mode. No signature of asymmetric quasifission is observed. The MD widths show a linear dependence with the measured energies.

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Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna, 141980, Russian Federation
Institute of Nuclear Physics of the Ministry of Energy of the Republic of Kazakhstan, Almaty, 050032, Kazakhstan

Flerov Laboratory of Nuclear Reactions
Institute of Nuclear Physics of the Ministry of Energy of the Republic of Kazakhstan

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