Mass and isospin dependence of symmetry energy coefficients of finite nuclei

The mass and isospin dependence of symmetry energy coefficients asym of finite nuclei are investigated with the measured nuclear masses incorporating the liquid drop mass formula. The enhanced asym for nearly symmetric nuclei are observed. To describe the mass and isospin dependence of asym, a modified formula based on the conventional surface-symmetry term is proposed and the corresponding rms deviation of nuclear masses is checked.