Empirical formula for the excitation energies of the first $2^+$ and $3^-$ states in even-even nuclei

Abstract

We report empirical findings that a simple formula in terms of the mass number $A$, the valence proton number $N_p$, and the valence neutron number $N_n$ can describe the essential trends of excitation energies $E_x$ of the first $2^+$ and $3^-$ states in even-even nuclei throughout the periodic table. The formula reads as $E_x = \alpha A^{-\beta} + \exp (- \lambda N_p) + \exp (- \lambda N_n)$. The parameter $\beta$ in the first term is determined by the mass number $A$ dependence of the bottom contour line of the excitation energy systematics. The other two parameters $\alpha$ and $\lambda$ are fitted by minimizing the $\chi^2$ value between the measured and calculated excitation energies. Our results suggest that the single large-$j$ shell simulation can be applied to the excitation energies of the first $2^+$ and $3^-$ states in even-even nuclei.