The expanding dynamics in central ${}^{129}$ Xe + ${}^{120}$Sn collisions at 50 MeV/nucleon is investigated within the framework of the isospin-dependent quantum molecular dynamics model in combination with the statistical decay code gemini. The nonisotropic distributions in the fragment size and average kinetic energy are reproduced. The collective expansion energy and the Coulomb explosion energy of different fragments are extracted. We focus on the nonisotropic explosion of the colliding system and the difference of explosion energies of H, He, Li, and Be fragments. The radial flow energies are extracted at the polar angle ${\theta }_{c.m.}$ = 90${}^{\circ }$. From studying the beam energy dependence at 50–125 MeV/nucleon, the threshold energies of the radial flow are investigated. The time evolutions of the density and the collective velocity are investigated. It is found that the radial flow causes the system to expand in the isotropic direction, whereas the residual incident energy causes the system to extend along the longitudinal direction. The Pauli blocking is responsible for the nonisotropic nature of the collective velocity.

• Received 9 June 2013

DOI:https://doi.org/10.1103/PhysRevC.89.014619