Isospin effects on intermediate mass fragments at intermediate energy-heavy ion collisions

In this study, we investigated the isospin properties of intermediate mass fragments (IMFs) for the central Sn-112,Sn-124+Sn-112,Sn-124 collisions of Sn at a beam energy of 50 MeV per nucleon using an improved quantum molecular dynamics model (ImQMD) coupled with a sequential decay model (GEMINI). Three observables were analyzed: (1) the average center-of-mass kinetic energy per nucleon < E-c.m./A > of fragments as a function of their charge number Z; (2) the average neutron number to proton number ratio (< N >/Z) of fragments with a given charge number Z as a function of their center-of-mass kinetic energy per nucleon (E-c.m./A); and (3) the average total neutron number to total proton number ratio (Sigma N/Sigma Z) and double ratio (DR(N/Z)) of IMFs with Z = 3-8 as a function of their center-of-mass kinetic energy per nucleon E-c.m./A. Our calculations revealed that the sensitivity of the isospin properties of IMFs relative to the stiffness of the symmetry energy remains even after sequential decay. By comparing the calculations of Sigma N/Sigma Z and DR(N/Z) with the data, it was found that the soft symmetry energy, i.e., gamma = 0.5, is favored.

Automated summary

In this study, the isospin properties of intermediate mass fragments (IMFs) produced in Sn collisions were investigated using the ImQMD model coupled with the GEMINI model. Three observables were analyzed, and the calculations showed that the isospin properties of IMFs were sensitive to the stiffness of the symmetry energy, favoring a soft symmetry energy (gamma=0.5).