Symmetry and pairing energies of atomic nuclei

Abstract

A global investigation of the symmetry and pairing energies of atomic nuclei has been undertaken based on excitation energy differences between isobaric analog states. The symmetry energies display pronounced shell effects. An isospin-based shell-model formalism describes the characteristics of nuclei with neutrons and protons in the same orbits quite well. However, unexpected structures are seen for nuclei in a region near A≈84 with N≈ Z which reflects on quartet ( α-particle-like) structures in agreement with theoretical prediction. A particle–hole formalism has been applied to nuclei with neutrons and protons in different shell-model orbits. The average neutron–proton interaction depends on the sum of two terms which are proportional to the product of the number of particles and holes and to the number of particles. Good agreement has been achieved with the experimental data except for the heaviest nuclei.