将反转岛南岸延伸至$^{28}$ F
Extending the Southern Shore of the Island of Inversion to $^{28}$F
摘要：
详细的光谱学的中子游离核$^{28}$ F已被执行的第一次质子/中子删除后，从$^{29}$ Ne/ $^{29}$ F束在能量约230 MeV/核子。重建了$^{27}$ F $^{(*)}+n$和$^{26}$ F $^{(*)}+2n$符合的不变质谱，并显示了一系列明确的共振。在两个反应中观察到一个近阈值状态，并确定为$^{28}$ F基态，$S_n(^{28}$ F $)=-199(6)$ keV，而$2n$衰变通道的分析允许一个相当大的改进$S_n(^{27}$ F $)=1620(60)$ keV的推导。与壳模型预测和eikonal模型反应计算的比较，允许自旋宇称分配提出的一些较低的水平的$^{28}$ F。重要的是，在基态的情况下，重建的$^{27}$ F $+n$动量分布后，从$^{29}$ F中子去除表明，它主要来自$1p_{3/2}$中子入侵者配置。这表明$N=20$周围的反转岛包括$^{28}$ F，而且很可能包括$^{29}$ F，并表明$^{28}$ O不是双魔。
英文摘要：
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.
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