Fusion-fission study at JAEA for heavy-element synthesis

Nishio, Katsuhisa   

Fission fragment mass and kinetic energy distributions were measured in the reactions of Si,P,S,Ar,Ca + U at energies around the Coulomb barrier. The mass distributions changed drastically with incident energy. The results are explained by a change of the ratio between fusion and qasifission with nuclear orientation. A calculation based on a fluctuation dissipation model reproduced the mass distributions and their energy dependence. Fusion probabilities are defined as the ratio of fusion-fission events to the total fission events. They were used to determine the cross section to produce super-heavy nucleus (SHN) in a statistical model calculation. The calculated cross sections agreed with the experimental data for Sg and Hs produced in the reactions of Si + U and S + U, respectively. It is shown that the reaction at sub-barrier energies can be used for heavy element synthesis. In the measurement and analysis for Ca+U, we also estimated that the copernicium isotopes (Z=112) can be produced at lower incident energies than those used so far, suggested that more neutron rich SHN can be produced with smaller number of neutron evaporation.