Temperature and symmetry energy of neutron-rich fragments in the 1A GeV 124,136Xe+Pb reactions

In this work we study the symmetry-energy coefficient of neutron-rich nuclei, and the temperature dependence of nuclear symmetry energy at low temperatures. An isobaric method is used to extract the symmetry-energy coefficients of neutron-rich nucleus (asym) at zero temperature (T) and asym/T at nonzero temperature in the measured 1A GeV 124,136Xe+Pb reactions. T of fragment is obtained from the ratio of its asym to asym/T. The results show that, for fragment with the same neutron-excess (I=N‒Z), the heavier the fragment is, the higher T it has, and T tends to saturate around 1 MeV for the large mass fragments. It is also shown that the more neutron-rich the isobar is, the higher temperature it has. The T2 dependence of symmetry energy of finite nucleus at low temperatures is verified by the extracted results.