Figure 3: Fission fragment yield of 236U. Still, we compare here theĬalculated results for only first chance fission with experimental data, since it is not our purpose to fit the data with our model rather, we wish to understand the reaction mechanisms in terms of the fluctuation dissipation dynamics. The effect of multi chance fission may be estimated by using the Hauser-Feshbach model calculation with generically available codes such as TALYS Koning et al. We are aware of the fact that there are contributions from second and third chance fission above several MeV. The upper limit of the excitation energy was In this section, we compare the calculated mass distributions with experimental information. Figure 1: The two center shell model shape profile. Thus, in nuclear fission at low excitations the application of macroscopic transport coefficients is not well justified. ( 1997) Ivanyuk and Hofmann ( 1999) that the mass and friction coefficients derived within a microscopic approach at low excitation energies differ drastically from their macroscopic counterparts in dependence on both the deformation and excitation energy (temperature). These quantities do not contain any quantum effects. ( 1976) for the inertia and the wall-and-window formula Blocki et al. The tensors of friction and inertia are calculated within macroscopic models: the Werner-Wheeler method Davies et al. In all these works only potential energy is calculated accurately enough mainly within the macroscopic-microscopic method which combines liquid-drop properties of fissioning nuclei with quantum shell and pairing effects. ( 2016a) Pahlavani and Mirfathi ( 2015) Mazurek et al. In nuclear fission, the random force is due to the sum of fluctuations resulting from the complex changes of each individual nucleons movements acting on the collective coordinates.Īt present there are several groups using the Langevin approach for the description of fission processes Mazurek et al. The Langevin approach extends the classical Newtonian equation by adding a random force. We keep only a small number of collective coordinates which are convenient to describe nuclear fission assuming that the time-evolution of the collective shape of the nucleon distribution can be described by the classical treatment. On the other hand, in the Langevin description of fission, However, it is not possible yet to treat the nuclear fission starting from the compound nuclei all the way to scission by these microscopic theories. The motion of each individual nucleon can be taken into account in approaches such as time-dependent Hartree-Fock theory or molecular dynamics that consider the degrees of freedom of all nucleons in the system quantum-mechanically. The nuclear fission phenomena is very fascinating because it involves a large-scale restructuring of nucleon arrangements. ![]() ![]() The results obtained with microscopic transport coefficients are much closer to experimental data than those calculated with macroscopic ones. ![]() It was also found that transport coefficients (friction and inertia tensors) calculated by a microscopic model and by macroscopic models give drastically different behavior of TKE as a function of excitation energy. The decomposition of TKE into the prescission kinetic energy and Coulomb repulsion showed that decrease of TKE with growing excitation energy is accompanied by a decrease of prescission kinetic energy. In the mass-energy distributions of fission fragments we see the contributions from the standard, super-long and super-short (in the case of 258Fm) fission modes.įor the fission fragments mass distribution of 258Fm we obtained a single peak mass distribution. This allowed us to establish systematic trends of TKE with Z 2 / A 1 / 3 of the fissioning system and as a function of excitation energy. We analyzed the total kinetic energy (TKE) of fission fragments with three-dimensional Langevin calculations for a series of actinides and Fm isotopes at various excitation energies. Theoretical Division, National Astronomical Observatory of Japan, 2 chome-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan. Nuclear Theory Department, Institute for Nuclear Research, Prospect Nauki 47, 03028 Kiev, Ukraine. Reactor Technology Center, Technical Support Division, Malaysia Nuclear Agency, Bangi, 43000 Kajang, Selangor Darul Ehsan, Malaysia. Laboratory for Advanced Nuclear Energy, Institute of Innovative Research, Tokyo Institute of Technology, 2 chome-12-1 Ookayama, Meguro, Tokyo 152-8550, Japan.
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