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 ⁸⁰Zr 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 ⁸⁰Zr through high-precision Penning trap mass measurements of ^80–83Zr. Our mass values show that ⁸⁰Zr 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.

原子核中的质子和中子在壳中移动，类似于原子的电子壳结构。核壳结构因核平均场随中子数N和质子数Z的变化而变化，这些变化可以通过测量原子核之间的质量差异来探测。N  =  Z = 40自 共轭核⁸⁰ Zr 特别令人感兴趣，因为它的质子和中子壳结构预计非常相似，并且其基态高度变形。^{在这里，我们通过80-83}的高精度 Penning 陷阱质量测量提供了在⁸⁰ Zr中存在变形双壳闭合的证据锆。我们的质量值显示⁸⁰ Zr 比预期的要轻得多，因此束缚力更强。这可以归因于N  =  Z  = 40 处的变形壳闭合和大的 Wigner 能量。使用几个全局核质量模型的统计贝叶斯模型混合分析表明，使用当前理论再现观察到的质量异常存在困难。