Within the framework of Lanzhou quantum molecular-dynamics transport model, the correlation of initial configuration and symmetry energy is systematically investigated in collisions of ${}^{238}\mathrm{U}+{}^{238}\mathrm{U}$. The impacts of the collision centrality (angular momentum), beam energy, stiffness of symmetry energy, and initial configuration on the collective flows, neutron/proton, and ${\pi }^{-}/{\pi }^{+}$ ratios have been thoroughly analyzed. It is found that the broader neutron-rich region is formed in the body-body collisions in comparison with the ones in the tip-tip collisions. The neutron-star matter might be created in the density region of 0.2–0.5 ${\rho }_0$ (the normal nuclear density ${\rho }_0=0.165{\mathrm{fm}}^{-3}$) formed in the ${}^{238}\mathrm{U}+{}^{238}\mathrm{U}$ reaction at the incident energy of 500 MeV/nucleon. The elliptic flows of protons are related to the incident energy, collision centrality, symmetry energy, and collision orientation. The hard-symmetry energy enables the larger free neutron/proton ratio at the beam energy of 500 MeV/nucleon. However, the neutron/proton and ${\pi }^{-}/{\pi }^{+}$ ratios in the density regime of $1.2\le \rho /{\rho }_0\le 1.8$ are enhanced by the soft-symmetry energy with the slope parameter of $\mathrm{L}=42$ MeV.

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• Collective flow
• Nuclear matter in neutron stars
• Nuclear reactions