Nucleon-nucleon cross sections in neutron-rich matter and isospin transport in heavy-ion reactions at intermediate energies
Nucleon-nucleon cross sections in neutron-rich matter and isospin transport in heavy-ion reactions at intermediate energies
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DOI：
10.1103/physrevc.72.064611
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发表时间：
2005-08
影响因子：
3.1
通讯作者：
Bao-An Li;Lie-Wen Chen
中科院分区：
文献类型：
--
作者：
Bao-An Li;Lie-Wen Chen
根据密度、动量和同位旋相关核子有效质量，使用比例模型评估富中子物质中的核子-核子 (NN) 横截面。研究发现，与自由空间相比，介质中的神经网络横截面不仅减小了，而且具有不同的同位旋依赖性。由于中子-质子有效质量分裂，nn 和 pp 散射截面之间的差异随着介质同位旋不对称性的增加而增加。在传输模型 IBUU04 中，发现介质内 NN 横截面显着影响重离子反应中的同位旋传输。对于介质内的 NN 横截面，对称能量为 ${E}_{\mathrm{sym}}(\ensuremath{\rho})\ensuremath{\approx}31.6(\ensuremath{\rho}/{\ensuremath{\rho}}_{0}){}^{0.69}$ 与以下两种方法相比是最可接受的 MSU 同位旋扩散数据和目前可接受的中子皮厚度 $^{208}\mathrm{Pb}$。同位旋核不可压缩性的同位旋相关部分 ${K}_{\mathrm{asy}}({\ensuremath{\rho}}_{0})$ 进一步缩小到 $\ensuremath{-}500\ifmmode\pm\else\textpm\fi{}50$ MeV。还研究了同时确定介质内神经网络横截面和对称能的可能性。质子横向流，或者更好的是中子和质子的组合横向流，可以用作介质内 NN 横截面的探针，而不会受到对称能不确定性的太大阻碍。
Nucleon-nucleon (NN) cross sections are evaluated in neutron-rich matter using a scaling model according to density, momentum, and isospin dependent nucleon effective masses. It is found that the in-medium NN cross sections are not only reduced but also have a different isospin dependence compared with the free-space ones. Because of the neutron-proton effective mass splitting the difference between nn and pp scattering cross sections increases with the increasing isospin asymmetry of the medium. Within the transport model IBUU04, the in-medium NN cross sections are found to influence significantly the isospin transport in heavy-ion reactions. With the in-medium NN cross sections, a symmetry energy of ${E}_{\mathrm{sym}}(\ensuremath{\rho})\ensuremath{\approx}31.6(\ensuremath{\rho}/{\ensuremath{\rho}}_{0}){}^{0.69}$ was found most acceptable compared with both the MSU isospin diffusion data and the presently acceptable neutron-skin thickness in $^{208}\mathrm{Pb}$. The isospin dependent part ${K}_{\mathrm{asy}}({\ensuremath{\rho}}_{0})$ of isobaric nuclear incompressibility was further narrowed down to $\ensuremath{-}500\ifmmode\pm\else\textpm\fi{}50$ MeV. The possibility of determining simultaneously the in-medium NN cross sections and the symmetry energy was also studied. The proton transverse flow, or even better the combined transverse flow of neutrons and protons, can be used as a probe of the in-medium NN cross sections without much hindrance from the uncertainties of the symmetry energy.