Symmetry energy and experimentally observed cold fragments in intermediate heavy-ion collisions**Supported by National Natural Science Foundation of China (U1432247, 11605097), National Basic Research Program of China (973 Program, 2014CB845405), Doctoral Scientific Research Foundation of Inner Mongolia University for the Nationalities (BS365)

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An attempt is made to study the symmetry energy at the time of primary fragment formation from the experimentally observed cold fragments for a neutron-rich system of 64Ni + 9Be at 140 MeV/nucleon, utilizing the recent finding that the excitation energy becomes lower for more neutron-rich isotopes with a given Z value. The extracted asym/T values from the cold fragments, based on the Modified Fisher Model (MFM), are compared to those from the primary fragments of the antisymmetrized molecular dynamics (AMD) simulation and become consistent with the simulation when the I = N − Z value becomes larger, indicating that the excitation energy of these neutron-rich isotopes is indeed lower.