Isobaric yield ratios and the symmetry energy in heavy-ion reactions near the Fermi energy

摘要

The relative isobaric yields of fragments produced in a series of heavy-ion-induced multifragmentationnreactions have been analyzed in the framework of a modified Fisher model, primarily to determine the rationof the symmetry energy coefficient to the temperature, asym/T , as a function of fragment mass A. The extractednvalues increase from 5 to ∼16 as A increases from 9 to 37. These values have been compared to the results ofncalculations using the antisymmetrized molecular dynamics (AMD) model together with the statistical decayncode GEMINI. The calculated ratios are in good agreement with those extracted from the experiment. In contrast,nthe values extracted from the ratios of the primary isobars from the AMD model calculation are ∼4 to 5 and shownlittle variation with A. This observation indicates that the value of the symmetry energy coefficient derived fromnfinal fragment observables may be significantly different than the actual value at the time of fragment formation.nThe experimentally observed pairing effect is also studied within the same simulations. The Coulomb coefficientnis also discussed