AI 中文总结
本文开发幺正极限下的四中子晕模型，应用于$^{22}$C、$^{19}$B、$^{14}$Be，计算得$^{22}$C和$^{19}$B物质半径与实验值吻合，$^{14}$Be电荷半径与推导值一致，揭示了四中子晕结构随标度比值的演化规律。
AI 中文摘要
在通常被视为双中子晕的一些丰中子核中，核心本身可分解为亚核心-中子-中子子系统，因此可能涉及四个价中子。为描述该情况，本文开发了幺正极限下的四中子晕模型，并将其应用于$^{22}$C、$^{19}$B和$^{14}$Be；这些核具有紧凑的核核心，周围被两个弱束缚的自旋单态中子对占据不同空间壳层，特征为两个独立的动量标度，且四中子波函数完全反对称化。本文绘制了晕结构随两个标度比值的演化：从标度分离良好的极限（此时系统退化为围绕结构化核心的有效双中子晕）到标度相当的区域（此时四中子特征完全显现）。在中间比值处，识别出一个窗口，其中无量纲均方根距离对标度层级不敏感，系统近似表现为单标度构型。计算得到的$^{22}$C和$^{19}$B的物质半径与最新实验值一致，且在当前不确定度范围内，物质半径无法区分$^{22}$C的有效双中子晕描述与显式四中子晕描述；区分这两种图像需要对晕分布形状敏感的观测量，例如高阶径向矩的比值。对于$^{14}$Be，计算得到的电荷半径与从测量的点质子半径推导得到的值一致。
英文摘要
In some neutron-rich nuclei usually treated as two-neutron halos, the core can itself be resolved into a subcore-neutron-neutron subsystem, so that four valence neutrons may be involved. To describe this situation, a four-neutron halo model in the unitary limit is developed and applied to $^{22}$C, $^{19}$B, and $^{14}$Be, in which a compact nuclear core is surrounded by two weakly bound spin-singlet neutron pairs occupying different spatial shells, characterized by two independent momentum scales, with the four-neutron wave function fully antisymmetrized. The evolution of the halo structure with the ratio of the two scales is mapped from the limit of well-separated scales, where the system reduces to an effective two-neutron halo around a structured core, to the regime of comparable scales, where the four-neutron character is fully developed. At intermediate ratios, a window is identified in which the dimensionless root-mean-square distances become insensitive to the scale hierarchy and the system behaves approximately as a one-scale configuration. The calculated matter radii of $^{22}$C and $^{19}$B are consistent with the most recent experimental values and, within current uncertainties, the matter radius does not discriminate between an effective two-neutron-halo and an explicit four-neutron-halo description of $^{22}$C. Distinguishing the two pictures requires observables sensitive to the shape of the halo distribution, such as ratios of higher radial moments. For $^{14}$Be, the computed charge radius is consistent with the value derived from the measured point-proton radius.
