Lightweight self-conjugate nucleus ${}^{80}$Zr

Abstract

Protons and neutrons in the atomic nucleus move in shells analogous to the electronic shell structures of atoms. Nuclear shell structure varies across the nuclear landscape due to changes of the nuclear mean field with the number of neutrons $N$ and protons $Z$. These variations can be probed with mass differences. The $N=Z=40$ self-conjugate nucleus ${}^{80}$Zr is of particular interest as its proton and neutron shell structures are expected to be very similar, and its ground state is highly deformed. In this work, we provide evidence for the existence of a deformed double shell closure in ${}^{80}$Zr through high precision Penning trap mass measurements of ${}^{80-83}$Zr. Our new mass values show that ${}^{80}$Zr is significantly lighter, and thus more bound than previously determined. This can be attributed to the deformed shell closure at $N=Z=40$ and the large Wigner energy. Our statistical Bayesian model mixing analysis employing several global nuclear mass models demonstrates difficulties with reproducing the observed mass anomaly using current theory.

arXiv comment11 pages; 5 figures; submitted version, revised version accepted in Nature Physics pending minor revisions

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• Machine Learning in Nuclear Physics
• Performing Bayesian analyses with AZURE2 using BRICK: an application to the ${}^7$Be system
• Ab initio computations of strongly deformed nuclei around ${}^{80}$Zr
• High-precision mass measurements of neutron deficient silver isotopes probe the robustness of the $N$ = 50 shell closure
• Constraining the Synthesis of the Lightest p Nucleus 74Se
• Collision-Induced Dissociation at TRIUMF's Ion Trap for Atomic and Nuclear science
• Tetrahedral shape and Lambda impurity effect in ${}^{80}$Zr with a multidimensionally constrained relativistic Hartree-Bogoliubov model
• Mass Probe of Tetrahedral Symmetry in Atomic Nuclei
• Further exploration of the machine-learning-based nuclear mass table