Going Beyond the Neutron Drip-Line with MoNA

Abstract

Understanding the structure of very neutron-rich nuclei is critical to developing reliable and robust models of the nucleus. For nuclei near the neutron drip-line, where the neutron removal energy approaches zero, several features of nuclear structure are much more important than they are in stable nuclei. The neutron pairing energy becomes comparable to the neutron removal energy and nuclei with odd neutron numbers tend to be unbound while their even neighbors remain bound. Additionally, shell effects can be greatly altered by the absence of protons in the same valence orbitals occupied by the neutrons. The lack of the stabilizing influence of protons in similar orbits allows for the tensor interaction between these weakly bound neutrons and the core nucleons to alter the energies of single particle levels. These changes lead to the disappearance of well-known magic numbers and the appearance of new sub-shell closures that have the requisite properties of a magic number: enhanced stability, a large excitation energy for the first excited state, and spherical shape.