Global Calculations of Ground-State Axial Shape Asymmetry of Nuclei

TLDR

Nuclear ground‑state shapes are generally spheroidal, yet studies since the 1950s have identified hexadecapole components and a consensus that reflection symmetry is broken in some nuclei. The authors aim to compute axial symmetry breaking across the entire nuclear chart. They perform the first global calculation of axial symmetry breaking in nuclear ground states. The results show axial asymmetry where gamma bands are experimentally observed, and incorporating this removes systematic deviations between calculated and measured masses.

Abstract

Important insight into the symmetry properties of the nuclear ground-state (gs) shape is obtained from the characteristics of low-lying collective energy-level spectra. In the 1950s, experimental and theoretical studies showed that in the gs many nuclei are spheroidal in shape rather than spherical. Later, a hexadecapole component of the gs shape was identified. In the 1970-1995 time frame, a consensus that reflection symmetry of the gs shape was broken for some nuclei emerged. Here we present the first calculation across the nuclear chart of axial symmetry breaking in the nuclear gs. We show that we fulfill a necessary condition: Where we calculate axial symmetry breaking, characteristic gamma bands are observed experimentally. Moreover, we find that, for those nuclei where axial asymmetry is found, a systematic deviation between calculated and measured masses is removed.