^{238}U nucleus. An idea separation between fusion-fission and quasi-fission is shown in Fig.2, where potential energy surface and the typical trajectories for both types of fission are shown. The figure shows that fusion-fission and quasi-fission generate fragments with different mass asymmetry. Figure 3 shows the results of experiment. Quasi-fssion is characterized by the mass asymmetry, and the yields enhances with heavier projectile nuclei due to larger Coulomb repulsive force. The yield increases also with lowering the bombarding energy, which was explained by the effects of static deformation of

^{238}U on the reaction. The fusion probabilities were determined from the measured spectra with the help of Langevin model calculation. The estimated values could explain the cross sections of seaborgium and hassium isotopes produced in the reactions of

^{30}Si +

^{238}U [2] and

^{34}S +

^{238}U [3].

#### Fig.1 Process to produce super-heavy nuclei.

#### Fig.2 Potential energy landscape and shape evolution.

#### Fig.3 Fission fragment mass distributions reaction and incident energy leading to the compound nucleus are shown.

### References

[1] K. Nishio et al., Phys. Rev. C, 77, 064607 (2008).[2] K. Nishio et al., Phys. Rev. C, 82, 044604 (2010).

[3] K. Nishio et al., Phys Rev C 82, 024611 (2010).

[4] K. Nishio et al., Phys. Rev C, 86, 034608 (2012).