Decay ofBk246*formed in similar entrance channel reactions ofB11+U235andN14+Th232at low energies using the dynamical cluster-decay model

Abstract

The decay of the $^{246}\mathrm{Bk}$${}^{*}$ nucleus, formed in entrance channel reactions $^{11}\mathrm{B}+^{235}\mathrm{U}$ and $^{14}\mathrm{N}+^{232}\mathrm{Th}$ at different incident energies, is studied by using the dynamical cluster-decay model (DCM) extended to include the deformations and orientations of nuclei. The main decay mode here is fission. The other (weaker) decay channels are the light particles evaporation ($A\ensuremath{\leqslant}4$) and intermediate mass fragments ($5\ensuremath{\leqslant}A\ensuremath{\leqslant}20$). All decay products are calculated as emissions of preformed clusters through the interaction barriers. The calculated fission cross sections ${\ensuremath{\sigma}}_{\mathrm{fiss}}$, taken as a sum of the energetically favored symmetric and near symmetric fragments (${A}_{\mathrm{CN}}/2\ifmmode\pm\else\textpm\fi{}7$ and $A=106\text{\ensuremath{-}}110$ plus complementary fragments) show an excellent agreement with experimental data at all experimental incident c.m. energies for both reactions, except for the top three energies in the case of the $^{11}\mathrm{B}+^{235}\mathrm{U}$ reaction. The disagreement between the DCM calculations and data at higher incident c.m. energies for the $^{11}\mathrm{B}+^{235}\mathrm{U}$ entrance channel is associated with the presence of additional effects of noncompound, quasifission (qf) components, in contradiction with the measured anisotropy effects which indicate the other entrance channel $^{14}\mathrm{N}+^{232}\mathrm{Th}$ to contain the noncompound nucleus contribution. The prediction of two fission windows, the symmetric fission (SF) and near symmetric or heavy mass fragments (HMFs), suggests the presence of a fine structure of fission fragments, which also need an experimental verification. The only parameter of the model is the neck length parameter $▵R$ whose value is shown to depend strongly on limiting angular momentum, which in turn depends on the use of sticking or nonsticking moment of inertia for angular momentum effects.