Multimodality of 187Ir fission studied by the Langevin approach

Background: The fission mechanism of sub -lead nuclides remains unclear, especially the types of fission modes involved and their corresponding shell effects. Purpose: The aim is to identify the different modes in the fission of 187Ir, and investigate the corresponding mechanism. Method: The three-dimensional Langevin approach considering nucleus elongation, deformation, and mass asymmetry is applied to simulate fission dynamics. The macro -microscopic models are used to calculate the transport coefficients. Results: The fragment mass, deformation, and total kinetic energy (TKE) of 187Ir fission in the excitation energies range from 30 to 45 MeV are calculated. Based on the mass-TKE correlations, four fission modes are identified, namely two asymmetric standard modes, a symmetric superlong mode, and a symmetric liquid -drop mode. Strong excitation -energy resistance of two asymmetric modes is found. The mass distributions show the dominance of single -peak shape, which is in good agreement with experimental data. The fission potential energy surface and the fission dynamics are analyzed to investigate the origins of the modes and the competition between neutron and proton shell effects. Conclusions: Multiple fission modes are included in the 187Ir fission behind the single -peak -like distribution of observables. The proton and neutron magic numbers with different asymmetry parameter might heighten the sensitivity to the uncertainties of shell corrections.