Precision mass measurement of lightweight self-conjugate nucleus 80Zr

Protons and neutrons in the atomic nucleus move in shells analogous to the electronic shell structures of atoms. The nuclear shell structure varies as a result of changes in the nuclear mean field with the number of neutrons N and protons Z, and these variations can be probed by measuring the mass differences between nuclei. The N = Z = 40 self-conjugate nucleus Zr-80 is of particular interest, as its proton and neutron shell structures are expected to be very similar, and its ground state is highly deformed. Here we provide evidence for the existence of a deformed double-shell closure in Zr-80 through high-precision Penning trap mass measurements of Zr80-83. Our mass values show that Zr-80 is substantially lighter, and thus more strongly bound than predicted. This can be attributed to the deformed shell closure at N = Z = 40 and the large Wigner energy. A statistical Bayesian-model mixing analysis employing several global nuclear mass models demonstrates difficulties with reproducing the observed mass anomaly using current theory. High-precision mass measurements of exotic zirconium nuclei are reported, and reveal a double-shell closure for the deformed nucleus Zr-80, which is more strongly bound than previously thought.

Automated summary

This study provides evidence of a deformed double-shell closure in Zr-80 through high-precision mass measurements, showing that it is more strongly bound than previously thought. The findings suggest that there are still challenges in the field of nuclear physics, which require a combination of new observations and theoretical advancements for resolution.