标题： 考察$^{22}$铝中质子晕的证据 显示英文标题

标题： Examination of the evidence for a proton halo in $^{22}$Al

摘要： 近年来，越来越多的晕核或候选者在实验中被识别或提出。文中宣称，通过 $^{22}$Si 和 $^{22}$O 镜像 Gamow-Teller 跃迁中的大同位旋不对称性揭示了 $^{22}$Al 的晕结构 [Phys. Rev. Lett. 125, 192503 (2020)]。我们强调，在可能的不稳定核 $^{22}$Si 和双幻核 $^{22}$O 的波函数之间已经存在显著的镜像不对称性，这在很大程度上解释了观测到的跃迁不对称性。 此外，这些跃迁仅涉及子核 $^{22}$铝和 $^{22}$氟的 $1^+$激发态。由于 $^{22}$铝的 $1^+$态是质子非束缚态，因此不能将其视为晕态。 自旋-宇称分析表明， $^{22}$铝基态中的弱束缚 $2s_{1/2}$价质子不太可能。 为了研究基态铝-26 ($^{22}$Al) 的壳层结构，我们采用了最先进的变形和三轴相对论 Hartree-Bogoliubov 连续理论。 我们发现，只有在考虑三轴形变的情况下，弱束缚价质子的轻微 $s$-波成分才出现在铝-26 ($^{22}$Al) 中的 $5\%$。 尽管密度和均方根半径的分析表明，这种微小的 $s$-波成分不足以在铝-26 ($^{22}$Al) 中形成明显的质子晕，但其他近期理论结果报告了稍大的 $2s_{1/2}$占据数。 库仑势垒存在的情况下，需要多少个低-$\ell$组件才能形成质子晕的问题仍未解决。因此，未来测量反应或相互作用截面以及裂变碎片的动量分布是非常可取的，这有助于验证$^{22}$铝是否是一种晕核。 显示英文摘要

摘要： More and more halo nuclei or candidates have been identified or suggested in experiments in recent years. It was declared that the halo structure of $^{22}$Al is revealed by the large isospin asymmetry in $^{22}$Si/$^{22}$O mirror Gamow-Teller transitions [Phys. Rev. Lett. 125, 192503 (2020)]. We highlight that a significant mirror asymmetry already exists between wave functions of the likely unbound nucleus $^{22}$Si and the doubly-magic nucleus $^{22}$O, which largely explains the observed asymmetry in the transitions. Furthermore, these transitions involve only the $1^+$ excited states of the daughter nuclei $^{22}$Al and $^{22}$F. The $1^+$ state of $^{22}$Al cannot be considered a halo state due to its proton-unbound nature. An analysis of the spin-parity suggests that a weakly bound $2s_{1/2}$ valence proton in the ground state of $^{22}$Al is improbable. To investigate the shell structure for the ground state of $^{22}$Al, we employ the state-of-the-art deformed and triaxial relativistic Hartree-Bogoliubov theories in continuum. We find that a small $s$-wave component of $5\%$ appears for the weakly bound valence proton in $^{22}$Al only when triaxial deformation is considered. While the examination of densities and rms radii indicates that this small $s$-wave component is insufficient to form a discernible proton halo in $^{22}$Al, slightly larger $2s_{1/2}$ occupations have been reported in other recent theoretical results. The question of how many low-$\ell$ components are sufficient to form a proton halo in the presence of the Coulomb barrier remains open. Thus, future measurements of reaction or interaction cross sections and momentum distributions of breakup fragments are highly desirable to verify whether $^{22}$Al is a halo nucleus.