赝态方法中的双核子发射体：$^6$ Be和$^{16}$ Be的情况
Two-nucleon emitters within a pseudostate method: The case of $^6$Be and $^{16}$Be
摘要：
背景：自从第一次实验观测以来，双核子放射性在过去的15年里重新受到关注。$^6$ Be系统是最轻的双质子基态发射体，而$^{16}$ Be最近被认为是第一个观测到的双中子基态发射体。正确理解它们的性质和衰变模式需要对三体连续体进行合理的描述。目的：在一般的三体模型下研究了$^6$ Be和$^{16}$ Be的基态性质，并研究了它们在连续介质中的核子-核子关联。方法：在超球坐标系下，采用解析变换谐振子（THO）基，利用赝态（PS）方法构造了$^6$ Be和$^{16}$ Be基态波函数.这些共振近似为一个稳定的PS周围的已知的两核子分离能。有效的核心$N$势，约束的二元子系统$^5$ Li和$^{15}$ Be的实验信息，在计算中使用。结果如下：发现$^{16}$ Be的基态呈现强双中子组态，价中子主要占据相对于核心的$l=2$态。结果与以前的$R$ -矩阵计算的实际连续。$^6$ Be的情况显示出相对于它的镜像伙伴，双中子晕$^6$ He的明显对称性：双质子构型占主导地位，价质子占据$l=1$轨道。结论：PS方法是描述未结合$\text{core}+N+N$基态性质的一个合适的工具。对于$^{16}$ Be和$^6$ Be，结果与以前的理论研究一致，并确认占主导地位的双核子配置。这有利于相关的双核子发射的图像。
英文摘要：
Background: Since the first experimental observation, two-nucleon radioactivity has gained renewed attention over the past fifteen years. The $^6$Be system is the lightest two-proton ground-state emitter, while $^{16}$Be has been recently proposed to be the first two-neutron ground-state emitter ever observed. A proper understanding of their properties and decay modes requires a reasonable description of the three-body continuum. Purpose: Study the ground-state properties of $^6$Be and $^{16}$Be within a general three-body model and investigate their nucleon-nucleon correlations in the continuum. Method: The pseudostate (PS) method in hyperspherical coordinates, using the analytical transformed harmonic oscillator (THO) basis for three-body systems, is used to construct the $^6$Be and $^{16}$Be ground-state wave functions. These resonances are approximated as a stable PS around the known two-nucleon separation energy. Effective core-$N$ potentials, constrained by the available experimental information on the binary subsystems $^5$Li and $^{15}$Be, are employed in the calculations. Results: The ground state of $^{16}$Be is found to present a strong dineutron configuration, with the valence neutrons occupying mostly an $l=2$ state relative to the core. The results are consistent with previous $R$-matrix calculations for the actual continuum. The case of $^6$Be shows a clear symmetry with respect to its mirror partner, the two-neutron halo $^6$He: The diproton configuration is dominant, and the valence protons occupy an $l=1$ orbit. Conclusions: The PS method is found to be a suitable tool in describing the properties of unbound $\text{core}+N+N$ ground states. For both $^{16}$Be and $^6$Be, the results are consistent with previous theoretical studies and confirm the dominant dinucleon configuration. This favors the picture of a correlated two-nucleon emission.
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