NpNn scheme based on new empirical formula for excitation energy

Abstract

We examine the NpNn scheme based on a recently proposed simple empirical formula, which is highly valid for the excitation energy of the first excited natural parity even multipole states in even–even nuclei. We demonstrate explicitly that the NpNn scheme for the excitation energy emerges from the separate exponential dependence of the excitation energy on the valence nucleon numbers Np and Nn together with the fact that only a limited set of numbers is allowed for the Np and Nn of the existing nuclei.