Mass of 80Zr reveals a deformed double shell closure at N=Z=40

by Erich Leistenschneider (CERN)

Tuesday 5 Apr 2022, 16:15 → 18:15 Europe/Zurich

4/3-006 - TH Conference Room (CERN)

The nuclei that lie along the N=Z line form a rich laboratory for nuclear structure. The protons and neutrons in these nuclei occupy the same shell model orbitals, resulting in a large spatial overlap of single-particle wavefunctions and, therefore, permit unique isospin studies. In addition, midway along the N=Z line between the double-shell closures at 56Ni and 100Sn, a rapid change in nuclear shape is observed, giving rise to the most deformed ground states in the nuclear chart. These structural phenomena leave imprints on the binding energy that can be studied through mass spectroscopy. However, mass data in the upper N=Z region is sparse due primarily to low production yields.

In this presentation I will report on a recent experiment performed at the National Superconducting Cyclotron Laboratory that yielded the first Penning trap mass measurement of 80Zr [1], with N=Z=40. Our new mass values show that this nucleus is significantly lighter, and thus more bound than previously predicted. Through binding-energy indicators, we attribute this mass anomaly to the existence of a deformed double-shell closure at N=Z=40 and an increase in the Wigner energy of this exotic system. I will also show how several global nuclear mass models demonstrate difficulties with reproducing the observed phenomena and discuss our plans to revisit this region with the upcoming FRIB facility.

[1] A. Hamaker, E. Leistenschneider, R. Jain, et al. Precision mass measurement of lightweight self-conjugate nucleus 80Zr. Nat. Phys. 17, 1408–1412 (2021).