Mass and energy distributions of binary reaction products obtained in the reactions 22Ne+249Cf,26Mg+248Cm, 36S+238U, and 58Fe+208Pb have been measured. All reactions lead to Hs isotopes. At energies below the Coulomb barrier the bimodal fission of Hs*, formed in the reaction 26Mg+248Cm, is observed. In the reaction 36S+238U, leading to the formation of a similar compound nucleus, the main part of the symmetric fragments arises from the quasifission process. At energies above the Coulomb barrier fusion-fission is the main process leading to the formation of symmetric fragments for both reactions with Mg and S ions. In the case of the 58Fe+208Pb reaction the quasifission process dominates at all measured energies
Background:In heavy-ion-induced reactions the mechanism leading to the formation of the compound nucleus and the role of quasifission is still not clear. Purpose: Investigation of the quasifission process of superheavy composite systems with Z = 110-116 and comparison with properties of fusion-fission and quasifission of lighter composite systems. Method: Mass and energy distributions of fissionlike fragments formed in the reactions 48 Ca + 232 Th, 238 U, 244 Pu, and 248 Cm at energies near the Coulomb barrier have been measured using the double-arm time-of-flight spectrometer CORSET at the U-400 cyclotron of the FLNR JINR. Results: The most probable fragment masses as well as total kinetic energies and their dispersions in dependence on the interaction energies and ion-target combinations have been studied for asymmetric and symmetric fragments formed in the reactions. The capture cross sections were obtained for the reactions 48 Ca + 244 Pu and 248 Cm. The lower limits for fission barriers of 283−286 Cn, 289−292 Fl, and 293−296 Lv compound nuclei were estimated. Conclusions: Analysis of the properties of symmetric fragments has shown that a significant part of these fragments may be attributed to fusion-fission process for the reactions 48 Ca+ 238 U, 244 Pu, and 248 Cm.
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