Thermodynamic properties and shear viscosity over entropy density ratio of nuclear fireball in a quantum-molecular dynamics model

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Thermodynamic and transport properties of nuclear fireball created in the central region of heavy-ion collisions below 400 MeV/nucleon are investigated within the isospin-dependent quantum molecular dynamic (IQMD) model. These properties including the density, temperature, chemical potential, entropy density (s) and shear viscosity (η), are calculated by a generalized hot Thomas Fermi formulism and a parameterized function, which was developed by Danielewicz. As the collision goes on, a transient minimal η/s=5/4π-10/4π occurs in the largest compression stage. Besides, the relationship of η/s to temperature (T) in the freeze-out stage displays a local minimum which is about 9-20 times 1/4π around T = 8-12 MeV, which can be argued as indicative of a liquid gas phase transition. In addition, the influences of nucleon-nucleon (NN) cross section (σNN) and symmetry energy coefficient (Cₛ) are also discussed, and it is found that the results are sensitive to σNN but not to Cₛ.