The influence of the boundary conditions on characteristics of nuclear fission (original) (raw)
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Analysis of the total kinetic energy of fission fragments with the Langevin equation
Physical Review C, 2017
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. 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. In the mass-energy distributions of fission fragments we see the contributions from the standard, super-long and super-short (in the case of 258 Fm) fission modes. For the fission fragments mass distribution of 258 Fm we obtained a single peak mass distribution. 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. 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 results obtained with microscopic transport coefficients are much closer to experimental data than those calculated with macroscopic ones.
Critical insight into the influence of the potential energy surface on fission dynamics
Physical Review C, 2011
The present work is dedicated to a careful investigation of the influence of the potential energy surface on the fission process. The time evolution of nuclei at high excitation energy and angular momentum is studied by means of three-dimensional Langevin calculations performed for two different parametrizations of the macroscopic potential: the Finite Range Liquid Drop Model (FRLDM) and the Lublin-Strasbourg Drop (LSD) prescription. Depending on the mass of the system, the topology of the potential throughout the deformation space of interest in fission is observed to noticeably differ within these two approaches, due to the treatment of curvature effects. When utilized in the dynamical calculation as the driving potential, the FRLDM and LSD models yield similar results in the heavy-mass region, whereas the predictions can be strongly dependent on the PES for medium-mass nuclei. In particular, the mass, charge and total kinetic energy distributions of the fission fragments are found to be narrower with the LSD prescription. The influence of critical model parameters on our findings is carefully investigated. The present study sheds light on the experimental conditions and signatures well suited for constraining the parametrization of the macroscopic potential. Its implication regarding the interpretation of available experimental data is briefly discussed.
Scientific Reports, 2019
We have decomposed to symmetric and asymmetric modes the mass-TKE fission fragment distributions calculated by 4-dimensional Langevin approach and observed how the dominant fission mode and symmetric mode change as functions of {Z}^{2}/\sqrt[3]{A}$$ Z 2 / A 3 of the fissioning system in the actinides and trans-actinide region. As a result, we found that the symmetric mode makes a sudden transition from super-long to super short fission mode around 254Es. The dominant fission modes on the other hand, are persistently asymmetric except for 258Fm, 259Fm and 260Md when the dominant fission mode suddenly becomes symmetric although it returns to the asymmetric mode around 256No. These correlated “twin transitions” have been known empirically by Darleane Hoffman and her group back in 1989, but for the first time we have given a clear explanation in terms of a dynamical model of nuclear fission. More specifically, since we kept the shape model parameters unchanged over the entire mass reg...
Four-dimensional Langevin approach to low-energy nuclear fission of U236
Physical Review C, 2017
We developed a four-dimensional Langevin model which can treat the deformation of each fragment independently and applied it to low energy fission of 236 U, the compound system of the reaction n+ 235 U. The potential energy is calculated with the deformed two-center Woods-Saxon (TCWS) and the Nilsson type potential with the microscopic energy corrections following the Strutinsky method and BCS pairing. The transport coefficients are calculated by macroscopic prescriptions. It turned out that the deformation for the light and heavy fragments behaves differently, showing a sawtooth structure similar to that of the neutron multiplicities of the individual fragments ν(A). Furthermore, the measured total kinetic energy T KE(A) and its standard deviation are reproduced fairly well by the 4D Langevin model based on the TCWS potential in addition to the fission fragment mass distributions. The developed model allows a multi-parametric correlation analysis among, e.g., the three key fission observables, mass, TKE, and neutron multiplicity, which should be essential to elucidate several long-standing open problems in fission such as the sharing of the excitation energy between the fragments.
The Businaro--Gallone Region: A Playground for Dynamical Models of Fission?
Acta Physica Polonica B Proceedings Supplement, 2015
Nuclei in the Businaro-Gallone region are proposed as a relevant tool to study the dynamics of nuclear fission at high temperature. The influence of the macroscopic contribution to the driving potential energy landscape, and its strong dependence on angular momentum, is addressed in this contribution as a first step. An advanced model based on a four-dimensional Langevin approach is used to calculate fission-fragment mass and charge distributions. A good agreement with experiment is observed. The work is in progress, with the goal to explore the major assets of nuclei in this region for probing the modeling of inertia, friction and fluctuations, and particle evaporation.
Examination of isospin effects in multi-dimensional Langevin fission dynamics
Physics Letters B, 2010
One-dimensional and three-dimensional dynamical fission calculations based on Langevin equations are performed for the compound nuclei 194 Pb, 200 Pb, 206 Pb, 182 Hg, and 204 Hg to investigate the influence of the compound nucleus isospin on the prescission particle multiplicities and on the fission fragment mass-energy distribution. It is found that the prescission neutron, proton, and alpha particle multiplicities have approximately the same sensitivity to the dissipation strength for a given nucleus. This is at variance with conclusions of recent papers. The sensitivity of the calculated prescission particle multiplicities to the dissipation strength becomes higher with decreasing isospin of fissioning compound nucleus, and the increase of prescission particle multiplicities could reach 200%, when the reduction coefficient of onebody viscosity k s increases from 0.1 to 1, for the most neutron deficient nuclei considered. The variances of fission fragment mass and kinetic energy distributions are less sensitive to the change of dissipation strength than the prescission light particle multiplicities. A comparison to experimental data concerning 200 Pb nucleus is also presented.
Nuclear fission with a Langevin equation
Nuclear Physics A, 1993
1 A microscopically derived Langevin equation is applied to thermally induced nuclear fission. An important memory effect is pointed out and discussed. A strong friction coefficient, estimated from microscopic quantities, tends to decrease the stationary limit of the fission rate and to increase the transient time. The calculations are performed with a collective mass depending on the collective variable and with a constant mass. Fission rates calculated at different temperatures are shown and compared with previous available results.
Nuclear fission with diffusive dynamics
Physical Review C, 1992
We investigate the dynamics of nuclear fission, assuming purely diffusive motion up to the saddle point. The resulting Smoluchowski equation is solved for conditions appropriate to the ' 0+' Nd~'"Er reaction at 207 MeV. The solution is characterized by an equilibration time~0 for the system to reach steady state, and the fission decay rate in steady state, A. We find that the equilibration time~0 plays a very small role in determining the number of prescission neutrons. The diffusion coefficient extracted from the experimental data is larger than the theoretical in the work of Bush, Bertsch, and Brown by a factor of 5-11.
Fission observables from 4D Langevin calculations with macroscopic transport coefficients
EPJ Web of Conferences
We have extended the Langevin equations to 4 dimensions (4D) by allowing the independent deformation for the left (δ1) and right fragments (δ2) of the fissioning nucleus. At the moment we are only able to use them in conjunction with the macroscopic transport coefficients. Nevertheless, we can see a considerable improvement in the preliminary results for the fission observables, especially those related to the total kinetic energy (TKE) of fission fragments. By plotting the TKE distributions we have revealed the super-long fission modes in236U and super-short fission modes in257Fm. By plotting the distribution ofδagainst the fragment’s TKE we have noted a correlation between the values ofδand Brosa’s fission modes. We have found that the standard fission modes correspond to prolate tips of the light fragments while the complementary heavy fragments have oblate fission tips. On the other hand, if both fragments were prolate at the tips, we get super-long fission modes. If both fragme...