Research Nuclear Symmetry Energy And Bubble-like Structure With BUU Model

The symmetric energy and it’s density-dependent form which describe the isospin-dependent vector part of the equation of state（EOS）are very important for unstable nuclear structures and their reactions,the structure and evolution of neutron stars.The density distribution,which is is one of the most fundamental characters of atomic nucleus structure,could have an atypical form,bubble-like structure,due to the complexity of the nuclear force and quantum many-body system.Based on the BUU transport model,the density dependence of the symmetric energy of nuclear mater and the bubble-like structure of nuclei are studied,and the observables to the symmetry energy in high density and the method of detecting bubble structure with high energy proton are presented.Based on the Boltzmann-Uehling-Uhlenbeck（BUU）transport model,we fully consider the isospin-dependence of the model,including the isospin-dependent initialization of the coordinate space and momentum space of the nucleons,nucleon-nucleon scattering cross section,single parti-cle potential,Pauli blocking and so on.In order to reduce the statistical error,the number of events in each nuclear reaction simulation reaches millions to stabilize the analysis results.In the framework of BUU,the interactions of¹³²Sn+¹²⁴Sn and¹⁹⁷Au+¹⁹⁷Au with different impact parameters and beam energy were simulated,and sensitive regions of some nucleon observ-ables to the nuclear symmetry energy are studied.It is found that the symmetry-energy-sensitive ob-servable n/p ratio in the¹³²Sn+¹²⁴Sn reaction at 0.3 GeV/u in fact just probes the density-dependent symmetry energy below the density of 1.5ρ₀and effectively probes the density-dependent symme-try energy around or somewhat below the saturation density.Nucleon elliptic flow can probe the symmetry energy from the low-density region to the high-density region when changing the inci-dent beam energies from 0.3 to 0.6 GeV/u in the semi-central¹³²Sn+¹²⁴Sn reaction.And nucleon transverse and elliptic flows in the semi-central¹⁹⁷Au+¹⁹⁷Au reaction at 0.6 GeV/u are more sen-sitive to the high-density behavior of the nuclear symmetry energy.We thus conclude that nucleon observables in the heavy reaction system and with higher incident beam energy are more suitable to be used to probe the high-density behavior of the symmetry energy.With BUU model,nuclear bubble configuration in the hypothetical ⁴⁸Si nucleus is studied by proton induced central reaction at an incident beam energy of 0.8 GeV/u.It is found that the emitted protons in the beam direction are much more when the target has a hollow structure than does not have it while in the forward angles（nonzero angles）energetic protons are less scattered when the target has a hollow structure than does not have it.Both effects are enhanced for higher energy proton emission.Angle distribution of the energetic proton emission in the proton induced central reaction at a beam energy of 0.8 GeV/u thus can be a probe of the bubble configuration in target.The present study can also be used to probe some other potential bubble nuclei.The research thus provides a new way to probe the bubble configuration in nuclei.