Fission Modes and Fragment Shell Structures in ${}^{258}$Md${}^{\ast }$ from Six-Dimensional Langevin Calculations

Abstract

The fission of ${}^{258}{\mathrm{Md}}^{\ast }$ is calculated in the excitation energy range of $E^{\ast }=6$--$36$~MeV using a six-dimensional Langevin framework with the Cassini shape parametrization. The calculated events are classified into two symmetric and two asymmetric fission modes based on the fragment mass and the quadrupole deformations of the two fragments at scission. The symmetric modes are the short mode with high total kinetic energy (TKE) and the superlong mode with low TKE, whereas the asymmetric modes differ in mass asymmetry. With increasing excitation energy, the yield of the short mode decreases, whereas the combined yield of the two asymmetric modes increases, as observed in the in-beam prompt-fission study of ${}^{258}{\mathrm{Md}}^{\ast }$. From an analysis of the fragment shapes and associated single-particle levels, the short mode and the dominant asymmetric mode with the smaller mass asymmetry are found to involve a compact fragment characterized by deformed shell gaps at $Z=52$ and $N=84$, while the complementary fragment is compact in the short mode and strongly elongated in the asymmetric mode.

arXiv comment6 pages, 5 figures