标题： 魔力与超流性在$^{28}$O 附近的研究中的$^{30}$F 显示英文标题

标题： Magicity versus superfluidity around $^{28}$O viewed from the study of $^{30}$F

摘要： 中子丰富的未结合氟同位素$^{30}$F$_{21}$在 SAMURAI 光谱仪（RIBF，RIKEN）中首次通过测量其中子衰变被观测到，在 235 MeV/核子的$^{31}$Ne 核的准自由质子打靶反应中。 $^{30}$F 的质量以及因此而确定的一中子分离能从其不变质量谱的测量中确定为$S_n = -472\pm 58 \mathrm{(stat.)} \pm 33 \mathrm{(sys.)}$keV。 $S_n$($^{30}$F) 中没有出现明显的下降表明，在接近$^{28}$O 处，“魔”$N=20$壳层间隙并未恢复，这与我们的壳模型计算一致，计算预测中子$d$和$fp$轨道几乎简并，其中$1p_{3/2}$和$1p_{1/2}$轨道比$0f_{7/2}$轨道更紧密结合。 这种轨道的简并和重新排列有两个潜在后果：$^{28}$O 表现出像强超流核一样的特性，中子对在壳层间散射，而$^{29,31}$F 都似乎是非常好的两个中子晕核候选者。 显示英文摘要

摘要： The neutron-rich unbound fluorine isotope $^{30}$F$_{21}$ has been observed for the first time by measuring its neutron decay at the SAMURAI spectrometer (RIBF, RIKEN) in the quasi-free proton knockout reaction of $^{31}$Ne nuclei at 235 MeV/nucleon. The mass and thus one-neutron-separation energy of $^{30}$F has been determined to be $S_n = -472\pm 58 \mathrm{(stat.)} \pm 33 \mathrm{(sys.)}$ keV from the measurement of its invariant-mass spectrum. The absence of a sharp drop in $S_n$($^{30}$F) shows that the ``magic'' $N=20$ shell gap is not restored close to $^{28}$O, which is in agreement with our shell-model calculations that predict a near degeneracy between the neutron $d$ and $fp$ orbitals, with the $1p_{3/2}$ and $1p_{1/2}$ orbitals becoming more bound than the $0f_{7/2}$ one. This degeneracy and reordering of orbitals has two potential consequences: $^{28}$O behaves like a strongly superfluid nucleus with neutron pairs scattering across shells, and both $^{29,31}$F appear to be good two-neutron halo-nucleus candidates.