Statistical Features of the First Excitation Energy of Nuclei

The first excited state plays a significant role for all excited states of nuclei besides the ground state. The first excitation energy which can directly reflect the stability of the nuclei to some extent is one of the most important features of the excited states. Through statistical analysis of the first excitation energies of 2 125 nuclei, one can find that the first excitation energies at the traditional magic number positions are significantly higher than those of the adjacent nuclei, as well as the nuclei with the highest first excited energy of both the isotopic and isotonic chains. For a small number of nuclei significantly deviating from the positions of the traditional magic number, it is also found that their high first excitation energies were the Isobaric Analog States (IAS) of the adjacent nuclei or some mixed levels of fissile nuclei. For the highest first excitation energy of the isotopic and isotonic chains, the number of their spins and parities with 2⁺ of the first excited state is most up to 42%. For even-even nuclei in the range of mass number 100~200, the first excitation energies can be described by the exponential decay function with the valence nucleon N_pN_n.