Nuclear Techniques ›› 2014, Vol. 37 ›› Issue (10): 100516-100516.doi: 10.11889/j.0253-3219.2014.hjs.37.100516


Studies on the specific viscosity of nuclear matter formed in intermediate energy heavy ion collisions by using the isospin dependent quantum molecular dynamics model

ZHOU Chenglong MA Yugang FANG Deqing ZHANG Guoqiang CAO Xiguang   

  1. (Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Jiading Campus, Shanghai 201800, China)
  • Received:2014-08-14 Revised:2014-09-15 Online:2014-10-10 Published:2014-10-16

Abstract: Background: Specific viscosity, defined as the ratio of shear viscosity to entropy density, was found as a probe of phase transition. It was observed that the specific viscosity reaches a local minimum at the critical point for both macroscopic and microscopic systems. In addition, a universal lower boundary was predicted by the AdS/CFT theory. In intermediate energy heavy-ion collisions, the studies on the relationship of specific viscosity and nuclear liquid-gas phase transition are still rare. Purpose: This paper gives a brief review for our calculations of the specific viscosity of nuclear fireball created in head-on Au+Au collisions in intermediate energy, for the study of liquid-gas phase transition. Besides, the influences of nucleon-nucleon cross section and symmetry energy on the specific viscosity are also addressed. Methods: The hot Thomas-Fermi formalism is employed to extract the thermal properties of the nuclear matter which is located in the central region of the collision. Two different methods, the Green-Kubo and Danielewicz’s parameterized formula, are used to evaluate the shear viscosity. Finally the correlation between specific viscosity and temperature or collision energy is presented. Results: In both cases, a local minimum of specific viscosity which has the value of around 10 times of the lower bound is found at certain temperature or beam energy. It is clearly shown that the calculated results are not sensitive to the symmetry energy but strongly influenced by the nucleon-nucleon cross section. Conclusion: Our calculations demonstrate that a local minimum of specific viscosity can be taken as a probe of nuclear liquid-gas phase transition which takes place at around 10 MeV. Furthermore, the lower bound of specific viscosity is still valid for nuclear liquid-gas phase transition.

Key words: Intermediate energy heavy-ion collisions, Liquid-gas phase transition, Quantum molecular dynamics (QMD) model, Specific viscosity