富含中子的铂和金原子核的精确质量揭示了在双幻核\(^{208}Pb\)以下增强的\(N = 126\)壳层强度
Precision masses of neutron-rich platinum and gold nuclei reveal enhanced $N=126$ shell strength below doubly-magic $^{208}$Pb
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中文总结 AI 辅助
研究富含中子的铂和金原子核，通过在GSI用新方法测量其精确质量，发现\(N = 126\)同中子异位素结合更强，壳层强度增强，质子 - 中子相互作用有分支，重新定义核质量表面，为r过程核合成计算的理论模型提供基准。
中文摘要 AI 辅助
宇宙中最重的稳定原子核归因于量子壳层结构，即质子和中子分组到由间隙分隔的离散能级中。稳定原子核中已知最大的中子壳层间隙在\(N = 126\)，它使双幻核\(^{208}Pb\)稳定，并导致快速中子俘获过程（r过程）产生的金和铂附近重元素的特征丰度峰值。从铅中移除质子时，这个壳层间隙是否持续存在，是核结构和重元素合成建模的核心问题，但由于生产相关富含中子的原子核非常困难，一直未得到解答。此前该区域基本缺乏直接实验知识。本文报告了在GSI使用重离子存储环中肖特基和等时质谱的新组合对\(^{203,204}Pt\)和\(^{204,205,206}Au\)进行的首次精确质量测量。\(N = 126\)同中子异位素\(^{204}Pt\)和\(^{205}Au\)比先前已知质量表面的外推趋势分别更紧密结合403和464 keV，揭示了在双幻核\(^{208}Pb\)以下意外增强的\(N = 126\)壳层强度。此外随着质子从\(^{208}Pb\)中移除，质子 - 中子相互作用强度在\(N = 126\)处呈现出迄今未观察到的分支。我们的结果重新定义了富含中子的重元素区域中的核质量表面，并为理论模型提供了直接实验基准，这些模型对更奇特原子核的外推对于r过程核合成计算至关重要。
英文摘要
The heaviest stable nuclei in the universe owe their existence to quantum shell structure, the grouping of protons and neutrons into discrete energy levels separated by gaps. The largest known neutron shell gap in stable nuclei, at $N=126$, stabilizes doubly-magic $^{208}$Pb and is responsible for the characteristic abundance peak of heavy elements near gold and platinum produced by the rapid neutron-capture process (r-process). Whether this shell gap persists as protons are removed from lead is a question central to both nuclear structure and the modeling of heavy-element synthesis, yet it has remained unanswered due to the extraordinary difficulty of producing the relevant neutron-rich nuclei. Direct experimental knowledge in this region was essentially absent. Here we report the first precision mass measurements of $^{203,204}$Pt and $^{204,205,206}$Au, performed at GSI using a novel combination of Schottky and isochronous mass spectrometry in a heavy-ion storage ring. The $N=126$ isotones $^{204}$Pt and $^{205}$Au are more strongly bound than the extrapolated trend of the previously known mass surface by 403 and 464~keV, respectively, revealing an unexpectedly enhanced $N=126$ shell strength below doubly-magic $^{208}$Pb. Furthermore, the proton-neutron interaction strength exhibits a hitherto unobserved bifurcation at $N=126$ as protons are removed from $^{208}$Pb. Our results redefine the nuclear mass surface in the neutron-rich heavy-element region and provide direct experimental benchmarks for theoretical models whose extrapolations toward more exotic nuclei are essential for r-process nucleosynthesis calculations.
