Understanding the nuclear properties in the vicinity of ¹⁰⁰Sn, which has been suggested to be the heaviest doubly magic nucleus with proton number Z equal to neutron number N, has been a long-standing challenge for experimental and theoretical nuclear physics. In particular, contradictory experimental evidence exists regarding the role of nuclear collectivity in this region of the nuclear chart. Here, we provide further evidence for the doubly magic character of ¹⁰⁰Sn by measuring the ground-state electromagnetic moments and nuclear charge radii of indium (Z = 49) isotopes as N approaches 50 from above using precision laser spectroscopy. Our results span almost the complete range between the two major closed neutron shells at N = 50 and N = 82 and reveal parabolic trends as a function of the neutron number, with a clear reduction towards these two closed neutron shells. A detailed comparison between our experimental results and numerical results from two complementary nuclear many-body frameworks (density functional theory and ab initio methods) exposes deficiencies in nuclear models and establishes a benchmark for future theoretical developments.

理解¹⁰⁰ Sn 附近的核性质一直是实验和理论核物理的长期挑战，100 Sn 被认为是质子数Z等于中子数N的最重双魔核。特别是，关于核集体在核图表的这个区域中的作用存在矛盾的实验证据。在这里，我们通过使用精密激光光谱测量当N从上方接近 50 时，铟 ( Z = 49) 同位素的基态电磁矩和核电荷半径，为¹⁰⁰ Sn 的双重神奇特性提供了进一步的证据。我们的结果几乎涵盖了N = 50 和N = 82 处两个主要闭合中子壳层之间的整个范围，并揭示了作为中子数函数的抛物线趋势，并且明显向这两个闭合中子壳层减少。我们的实验结果与两个互补的核多体框架（密度泛函理论和从头计算方法）的数值结果之间的详细比较暴露了核模型的缺陷，并为未来的理论发展建立了基准。