IMF production and symmetry energy in heavy ion collisions near Fermi energy

Abstract: The symmetry energy at the time of the production of intermediate mass fragments (IMFs) is studied using experimentally observed IMF multiplicities combined with quantum statistical model calculations (QSM of Hahn and Stöcker). The ratios of difference in chemical potentials between neutrons and protons relative to the temperature, (μn−μp)/T, and the double ratio temperature, T, were extracted experimentally in the reactions of ^64,70Zn, ⁶⁴Ni+^58,64Ni, ^112,124Sn, ¹⁹⁷Au, ²³²Th at 40A MeV. The extracted (μn−μp)/T scales linearly with δ_NN, where δ_NN is the asymmetry parameter, (N–Z)/A, of the emitting source and (μn−μp)/T=(11.1±1.4)δNN−0.21 was derived. The experimentally extracted (μn−μp)/T and the double ratio temperatures are compared with those from the QSM calculations. The temperatures, T, and densities, ρ, extracted from the (μn−μp)/T values agreed with those from the double ratio thermometer which used the yield ratios of d, t, h and α particles. However the two analyses of the differential chemical potential analysis and the initial temperature analysis end up almost identical relation between T and ρ. T=5.25±0.75 MeV is evaluated from the (μn−μp)/T analysis, but no density determination was possible. From the extracted T value, the symmetry energy coefficient E_sym=14.6±3.5 MeV is determined for the emitting source of T=5.25±0.75 MeV.