Empirical formula extended to the yrast excitation energies of the unnatural parity states in even-even nuclei

Abstract

Recently, it was shown that a simple empirical formula, in terms of the mass and valence nucleon numbers, can describe the main trends of the yrast excitation energies of the natural parity states up to $10^+$ in even-even nuclei throughout the entire periodic table. The same empirical formula was applied to the yrast excitation energies of unnatural parity states including $1^+$, $2^-$, $3^+$, $4^-$, $5^+$, $6^-$, $7^+$, $8^-$, $9^+$, $10^-$, and $11^+$ in even-even nuclei. Although the overall character of the effective residual interaction for the unnatural parity states was quite different to that of the natural parity states, the same form of the empirical formula was found to hold reasonably well for the yrast excitation energies of the unnatural parity states.