The strength of the $N$ = 28 magic number in neutron-rich argon isotopes is examined through high-precision mass measurements of $^{46-48}$Ar, performed with the ISOLTRAP mass spectrometer at ISOLDE/CERN. The new mass values are up to 90 times more precise than previous measurements. While they suggest the persistence of the $N$ = 28 shell closure for argon, we show that this conclusion has to be nuanced in light of the wealth of spectroscopic data and theoretical investigations performed with the \emph{SDPF-U} phenomenological shell model interaction. Our results are also compared with \emph{ab initio} calculations using the Valence Space In-Medium Similarity Renormalization Group and the Self-Consistent Green's Function approaches. Both calculations provide a very good account of mass systematics at and around $Z$ = 18 and, generally, a consistent description of the physics in this region. This combined analysis indicates that $^{46}$Ar is the transition between the closed-shell $^{48}$Ca and collective $^{44}$S.

中文翻译：

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通过 Ar46–48 的高精度质量测量检查 N=28 壳闭合

富中子氩同位素中 $N$ = 28 幻数的强度通过 $^{46-48}$Ar 的高精度质量测量进行检查，该测量使用 ISOLDE/CERN 的 ISOLTRAP 质谱仪进行。新的质量值比以前的测量精确度高达 90 倍。虽然他们建议氩的 $N$ = 28 壳闭合的持久性，但我们表明，鉴于使用 \emph {SDPF-U} 现象学壳模型进行的大量光谱数据和理论研究，该结论必须有细微差别相互作用。我们的结果还与使用价空间介质中相似性重整化组和自洽格林函数方法的 \emph{ab initio} 计算进行了比较。两种计算都很好地说明了 $Z$ = 18 及附近的质量系统学，一般来说，对该区域物理的一致描述。这种组合分析表明 $^{46}$Ar 是闭壳 $^{48}$Ca 和集体 $^{44}$S 之间的过渡。