Dynamical Calculation of Multi-Modal Nuclear Fission of Fermium Nuclei

Abstract

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;

Two-mode fission – experimental verification and characterization of two fission-modes

“…The systematic features of the β values in the fission of actinides have been well reproduced by theoretical calculations based on the two-center shell model coupling with the dynamical calculations using the multi-dimensional Langevin equation [55]. Three types of the scission configurations in the fission of 264 Fm were pointed out as follows: mass-symmetric compact configuration, mass-asymmetric configuration, and mass-symmetric elongated configuration [55].…”

“…Three types of the scission configurations in the fission of 264 Fm were pointed out as follows: mass-symmetric compact configuration, mass-asymmetric configuration, and mass-symmetric elongated configuration [55]. Further Asano et al [55] calculated the mass-yield and TKE distributions for each type of the scission configurations.…”

Four-dimensional Langevin approach to low-energy nuclear fission of U236

“…The model can also determine the fission time scale, which is not the case for the Random-walk method [3]. At present there are several groups which use the Langevin approach for the description of the fission process [5,[7][8][9][10][11]. Due to the difficulty of the calculation of the multi-dimensional transport coefficients used in the Langevin equations, and due to the lack of sufficient resources for numerical calculations the number of shape parameters in most cases is restricted to 2 or 3 collective variables.…”

Systematic study for the mass distribution of fission fragments in the neutron rich region

“…In the Langevin equation, the hydro-dynamical mass tensor by Werner-Wheeler [17], the wall-and-window one-body dissipation tensor [18,19] and the random force whose strength satisfies the classical fluctuation-dissipation theorem are used. For several actinide nuclei, Ichikawa [20] and Asano [21] have calculated the fission paths for the purpose of the analysis of fission modes.…”

“…We can see the definite relation between this structure and the position of the valley in the PES near scission, when we draw the PES in the α − δ plane. By referring the results given by Ichikawa [20] and Asano [21], we planned to have a systematic analysis of the PES to make the data set on the fission fragment mass distribution in which both the symmetric and the asymmetric component are taken into account without details on the identification to various asymmetric modes. The guidelines of our estimation for the mass asymmetric parameter are the use of the PES in the α − δ plane, and the quantification of the depth of valley which has strong correlation with the thickness of the fission path or the measure of the mixture of different modes.…”