Detailed spectroscopy of the neutron-unbound nucleus ${}^{28}$F has been performed for the first time following proton/neutron removal from ${}^{29}$Ne/${}^{29}$F beams at energies around 230~MeV/nucleon. The invariant-mass spectra were reconstructed for both the ${}^{27}$F${}^{(*)}+n$ and ${}^{26}$F${}^{(*)}+2n$ coincidences and revealed a series of well-defined resonances. A near-threshold state was observed in both reactions and is identified as the ${}^{28}$F ground state, with $S_n{(}^{28}$F$)=-199(6)$~keV, while analysis of the $2n$ decay channel allowed a considerably improved $S_n{(}^{27}$F$)=1620(60)$~keV to be deduced. Comparison with shell-model predictions and eikonal-model reaction calculations have allowed spin-parity assignments to be proposed for some of the lower-lying levels of ${}^{28}$F. Importantly, in the case of the ground state, the reconstructed ${}^{27}$F$+n$ momentum distribution following neutron removal from ${}^{29}$F indicates that it arises mainly from the $1p_{3/2}$ neutron intruder configuration. This demonstrates that the island of inversion {around $N=20$} includes ${}^{28}$F, {and most probably ${}^{29}$F}, and suggests that ${}^{28}$O is not doubly magic.

中文翻译：

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将反转岛的南岸延伸到28F

中子未结合核的详细光谱 ${}^{28}$从质子/中子去除后首次进行F ${}^{29}$Ne /${}^{29}$F射线的能量约为230〜MeV /核子。重建了两个的不变质量谱${}^{27}$F${}^{（*）}+ñ$ 和 ${}^{26}$F${}^{（*）}+2ñ$巧合，并揭示了一系列明确的共鸣。在两个反应中均观察到接近阈值状态，并确定为${}^{28}$F基态 ${\mathrm{小号}}_{ñ}{（}^{28}$F$）=-199（6）$〜keV，同时分析 $2ñ$ 衰减通道可以大大改善 ${\mathrm{小号}}_{ñ}{（}^{27}$F$）=1620（60）$〜keV被推导。通过与壳模型预测和常规模型反应计算进行比较，可以提出一些较低水平的自旋平价分配方案。${}^{28}$F.重要的是，在基态的情况下， ${}^{27}$F$+ñ$ 从中子去除后的动量分布 ${}^{29}$F表示它主要来自 $\mathrm{1个}{p}_{3/2}$中子入侵者配置。这证明了反转之岛{$ñ=20$}包括 ${}^{28}$F，{而且很可能 ${}^{29}$F}，并建议 ${}^{28}$O不是双重魔法。