Multi-modal nuclear fission of fermium isotopes at low excitation energy is dynamically investigated. The multidimensional Langevin equation is used for the dynamical calculation. We use the potential energy taking account of the microscopic energy which depends on the excitation energy. We calculate the mass and the total kinetic energy (TKE) distributions of the fission fragments for Fm. The deformation of the fission fragments at the scission plays an important role in classifying the nuclear fission modes. We show that there exist following three types for the scission configuration classified by the shape of the fission fragments: mass-symmetric compact configuration, mass-asymmetric configuration, and mass-symmetric elongated configuration. We calculate the average mass number and the average TKE for each configuration. We also study the isotope dependence of the mass distribution of the fission fragments from three fermium isotopes.The multi-dimensional Langevin equation has the following form;

A mufti-dimensional Langevin equation is applied for the study of the multi-modal nuclear fission in actinide region. Two kinds issipation tensors, the wall-and-window formula and the wall formula, are used to investigate the dynamical effects of nuclear dissipation. The mass distribution and the total kinetic energy distribution of the fission fragments are calculated for 264F'm with these dissipation tensors. It is found that the dissipation tensor plays important roles in determining the fission paths. We obtain drastically different mass distributions by applying different models for nuclear friction.

We investigate fission modes of 270Sg with 3-dimensional Langevin equation. The shell correction energy is included in the total energy. The mass distribution and the total kinetic energy (TKE) distribution of fission fragments are calculated and are compared with the experimental results. Mass asymmetric fission dominates in the mode with the lower TKE, which is in agreement with the experimental result. The dynamics from saddle to scission is also discussed.

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The multi-modal fission of fermium nuclei is dynamically investigated. The multidimensional Langevin equation is used for the dynamical calculation. We use the potential energy taking account of the microscopic energy which depends on the excitation energy. We calculate the mass distribution and the total kinetic energy (TKE) distribution for 256 Fm. We study the excitation energy dependence of the mass and TKE distributions. We find that the excitation energy dependence comes from the change in the contribution of each fission mode. §1. IntroductionThe mass distribution and the total kinetic energy (TKE) distribution of the fission fragments consist of several components and these components correspond to nuclear fission modes. The phenomenon is observed for many nuclei. 1)-11)In studying the multi-modal nuclear fission, the fermium nuclei are very important from the viewpoint of magicity of the daughter nuclei since they separate into two proton-magic Sn (Z =50) nuclei in the mass-symmetric fission. For the thermal neutron induced fission of 255 Fm, it was found that the fission events with the high TKE correspond to a sharp mass-symmetric distribution and that with the low TKE corresponds to a mass-asymmetric distribution. 1) A mass-symmetric peak is observed in the thermal neutron induced fission of 255 Fm, while mass-asymmetric peaks are obtained in the spontaneous fission of 256 Fm. 1), 6) Namely, the position of the mass peak depends on the excitation energy.Zhao et al. investigated the systematics of the TKE in the actinide region. 10), 11) They assumed that the TKE is equal to the Coulomb energy at the scission configuration for point charges, namely TKE=Z 1 Z 2 e 2 /D, and defined the shape elongation at the scission point by β = D/(R 1 + R 2 ), where R 1,2 are the radii of fission fragments. They showed that there are mainly two types of scission configurations: a mass-asymmetric (A H =140) configuration with β =1.53 and a mass-symmetric elongated configuration with β =1.65. Additionally, there is a mass-symmetric compact configuration with β =1.33 in the heavy region where the mass number of the fissioning nucleus is nearly equal to 260.In our previous study, we succeeded in the classification of the fission events * )