Production probability of superheavy fragments at various initial deformations and orientations in the238U+238U reaction

Abstract

The dynamical effects of initial orientation and deformation (with and without ${\ensuremath{\beta}}_{4}$ deformation) of projectile and target on the ${}^{238}$U+${}^{238}$U reaction have been investigated by using the improved quantum molecular dynamics model. The deformation of colliding nuclei at touching configuration is distributed with a wide width, especially for the nose-nose orientation case. The influence of different orientations and deformations on the average lifetime of the transient composite system and the production probability of superheavy fragments (SHF) with $Zg110$ at incident energies 7--12 $A$ MeV is studied. The average lifetime of the composite system as a function of incident energy peaks at about 9--10 $A$ MeV for the side-side orientation and 11--12 $A$ MeV for the nose-nose orientation, respectively. The inclusion of ${\ensuremath{\beta}}_{4}$ deformation in prolate uranium seems to enhance the production probability of SHF in the side-side case as the more stable structure of initial uranium effectively reduces the excitation energy of the composite system. It is suggested that the optimal initial condition for production of SHF in ${}^{238}$U+${}^{238}$U could be the side-side orientation and prolate deformation with a small ${\ensuremath{\beta}}_{4}$ deformation (the ground state of uranium). Considering that the symmetry axis of the initial nuclei is oriented in an arbitrary direction with an equal probability, the lifetime of composite system and the SHF production probability are also studied with randomly selected orientation direction of initial nuclei.