Symmetry energy and the isoscaling properties of the fragments produced in ${}^{40}$Ar, ${}^{40}$Ca + ${}^{58}$Fe, ${}^{58}$Ni reactions at 25 $-$ 53 MeV/nucleon

Abstract

The symmetry energy and the isoscaling properties of the fragments produced in the multifragmentation of ${}^{40}$Ar, ${}^{40}$Ca + ${}^{58}$Fe, ${}^{58}$Ni reactions at 25 - 53 MeV/nucleon were investigated within the framework of statistical multifragmentation model. The isoscaling parameters $\hat{I}\pm$, from the primary (hot) and secondary (cold) fragment yield distributions, were studied as a function of excitation energy, isospin (neutron-to-proton asymmetry) and fragment symmetry energy. It is observed that the isoscaling parameter $\hat{I}\pm$ decreases with increasing excitation energy and decreasing symmetry energy. The parameter $\hat{I}\pm$ is also observed to increase with increasing difference in the isospin of the fragmenting system. The sequential decay of the primary fragments into secondary fragments, when studied as a function of excitation energy and isospin of the fragmenting system, show very little influence on the isoscaling parameter. The symmetry energy however, has a strong influence on the isospin properties of the hot fragments. The experimentally observed scaling parameters can be explained by symmetry energy that is significantly lower than that for the ground state nuclei near saturation density. The results indicate that the properties of hot nuclei at excitation energies, densities and isospin away from the normal ground state nuclei could be significantly different.

14 pages, 15 figures