Trajectory analysis for fusion path in superheavy-mass region

We propose an effective method for the precise investigation of the fusion-fission mechanism in the superheavy-mass region, using the fluctuation-dissipation model. The trajectory calculation with friction is performed in the nuclear deformation space using the Langevin equation. In the reaction $^{48}$Ca+$^{244}$Pu, the trajectories are classified into the fusion-fission process, the quasi-fission process and the deep quasi-fission process. By analyzing the time evolution of each trajectory, the mechanism of each process is clearly revealed, i.e., it is explained why a trajectory takes a characteristic path in this model. We discuss, in particular, the condition under which the fusion path is followed, which is crucial in the discussion of the possibility of synthesizing superheavy elements.Comment: 25 pages, 12 figures, accepted for publication in Nuclear Physics

Fusion hindrance and roles of shell effects in superheavy mass region

We present the first attempt of systematically investigating the effects of shell correction energy for a dynamical process, which includes fusion, fusion-fission and quasi-fission processes. In the superheavy mass region, for the fusion process, shell correction energy plays a very important role and enhances the fusion probability when the colliding partner has a strong shell structure. By analyzing the trajectory in three-dimensional coordinate space with the Langevin equation, we reveal the mechanism of the enhancement of the fusion probability caused by `cold fusion valleys'. The temperature dependence of shell correction energy is considered.Comment: 31 pages, 23 figures, Accepted for publication in Nuclear Physics

Pre-scission neutron multiplicity associated with the dynamical process in superheavy mass region

The fusion-fission process accompanied by neutron emission is studied in the superheavy-mass region on the basis of the fluctuation-dissipation model combined with a statistical model. The calculation of the trajectory or the shape evolution in the deformation space of the nucleus with neutron emission is performed. Each process (quasi-fission, fusion-fission, and deep quasi-fission processes) has a characteristic travelling time from the point of contact of colliding nuclei to the scission point. These dynamical aspects of the whole process are discussed in terms of the pre-scission neutron multiplicity, which depends on the time spent on each process. We have presented the details of the characteristics of our model calculation in the reactions $^{48}$Ca+$^{208}$Pb and $^{48}$Ca+$^{244}$Pu, and shown how the structure of the distribution of pre-scission neutron multiplicity depends on the incident energy.Comment: 19 pages, 12 figures, Accepted for publication in J. Phys.

Influence of microscopic transport coefficients on the formation probabilities for super-heavy elements

The formation probability is shown to increase by a few orders of magnitude if microscopic transport coefficients are used rather than those of the common macroscopic pictures. Quantum effects in collective dynamics are taken into account through the fluctuating force, as exhibited in diffusion coefficients for a Gaussian process. In the range of temperatures considered here, they turn out to be of lesser importance.Comment: 20 pages, 9 figures, replaced by revised version accepted for publication in NP