Background: In the "island of inversion", ground states of neutron-rich $sd$-shell nuclei exhibit strong admixtures of intruder configurations from the $fp$ shell. The nucleus $^{30}$Mg, located at the boundary of the island of inversion, serves as a cornerstone to track the structural evolution as one approaches this region. Purpose: Spin-parity assignments for excited states in $^{30}$Mg, especially negative-parity levels, have yet to be established. In the present work, the nuclear structure of $^{30}$Mg was investigated by in-beam $\gamma$-ray spectroscopy mainly focusing on firm spin-parity determinations. Method: High-intensity rare-isotope beams of $^{31}$Mg, $^{32}$Mg, $^{34}$Si, and $^{35}$P bombarded a Be target to induce nucleon removal reactions populating states in $^{30}$Mg. $\gamma$ rays were detected by the state-of-the-art $\gamma$-ray tracking array GRETINA. For the direct one-neutron removal reaction, final-state exclusive cross sections and parallel momentum distributions were deduced. Multi-nucleon removal reactions from different projectiles were exploited to gain complementary information. Results: With the aid of the parallel momentum distributions, an updated level scheme with revised spin-parity assignments was constructed. Spectroscopic factors associated with each state were also deduced. Conclusions: Results were confronted with large-scale shell-model calculations using two different effective interactions, showing excellent agreement with the present level scheme. However, a marked difference in the spectroscopic factors indicates that the full delineation of the transition into the island of inversion remains a challenge for theoretical models.

中文翻译：

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通过光束内 γ 射线光谱探索 Mg30 的结构

背景：在“反转岛”中，富含中子的 $sd$-壳核的基态表现出来自 $fp$ 壳的入侵者构型的强烈混合。核$^{30}$Mg 位于反转岛的边界处，当人们接近该区域时，它是跟踪结构演化的基石。目的：尚未确定 $^{30}$Mg 中激发态的自旋奇偶性分配，尤其是负奇偶性水平。在目前的工作中，$^{30}$Mg 的核结构是通过束内 $\gamma$ 射线光谱研究的，主要侧重于确定自旋平价。方法：$^{31}$Mg、$^{32}$Mg、$^{34}$Si 和 $^{35}$P 的高强度稀有同位素束轰击 Be 目标以诱导核子去除在 $^{30}$Mg 中填充状态的反应。$\gamma$ 射线是由最先进的 $\gamma$ 射线跟踪阵列 GRETINA 检测到的。对于直接去除一个中子的反应，推导出了终态专有截面和平行动量分布。利用来自不同射弹的多核子去除反应来获得补充信息。结果：在平行动量分布的帮助下，构建了具有修订自旋奇偶分配的更新水平方案。还推导出与每个状态相关的光谱因素。结论：结果面临着使用两种不同有效相互作用的大规模壳模型计算，显示出与当前水平方案的极好一致性。然而，