Keywords: 
• 对称能 /
• 有限核 /
• 核质量

Abstract: Nuclear symmetry energy characterizing the isospin dependent part of equation of state, is a hot topic in nuclear physics and astrophysics. Although many theoretical and experimental efforts have been performed, due to its di?culty, this problem remains unsolved. There are many approaches to deal with this issue, including nuclear many-body theories, heavy ion reactions, and nuclear giant resonances. Recently, significant progress has been made in constraining the density dependence of the symmetry energy around the saturation density. We explore the symmetry energy around the saturation density with the help of the properties of finite nuclei to reduce the uncertainty as far as possible. It is found that the symmetry energy (coe?cient) of 208Pb equals that of nuclear matter at reference density ρA=0.55 ρ0. This relation links the symmetry energy of the nuclear matter and the one of finite nuclei, with the help of which one can explore the density dependence of the symmetry energy. Thus, the central issue is to obtain the symmetry energy (coe?cient) of 208Pb. We exacted it with the experimentalβ?-decay energies of heavy nuclei and with nuclear mass differences, and then to constrain the density dependent symmetry energy at subsaturation density.