arXiv 1908.076932019-08nucl-th

核子对近似中对优化的变分方法

Variational approach for pair optimization in the nucleon pair approximation

Y. Lei, H. Jiang, S. Pittel

备注：: 16 pages, 6 figures
发表信息：: Phys. Rev. C 102, 024310 (2020)
DOI：: 10.1103/PhysRevC.102.024310

摘要：

本文提出了一种对凝聚变分方法（PCV），用以确定原子核低能态描述中最重要的一组集体对。获得这些关键集体对的精确细节-它们的自旋，宇称和结构-在基于核子对近似（NPA）的计算中特别有用，有助于减少它们的不确定性。在过渡Ba同位素的试验计算中，我们的变分方法描述了类似于Hartree-Fock处理的四极形变性质的演变，同时突出了$^{132}$ Ba的$γ$柔软性。我们的方法可以决定性地确定哪些集体对获得最低可能的yrast，准β，准γ带，产生这些带的水平结构和相关的B（E2）值与实验合理的一致性是至关重要的。这些试验计算表明，与我们的PCV方法的NPA可以有意义地适用于过渡核的广泛的形状。我们还表明，虽然中子负宇称对原则上可以有一个重要的影响回弯$^{132}$钡，他们不赞成这种核。

英文摘要：

We propose a pair-condensate variational approach (PCV) to determine a set of the most important collective pairs in the description of low-lying states in atomic nuclei. Having available the precise details on these key collective pairs -- their spin, parity, and structure -- can be particularly useful in calculations based on the nucleon-pair approximation (NPA), helping to reduce their uncertainties. In trial calculations for the transitional Ba isotopes, our variational approach describes the evolution of quadrupole-deformation properties similar to Hartree-Fock treatments, while at the same time highlighting the $γ$ softness of $^{132}$Ba. Our approach can conclusively determine which collective pairs are critical for obtaining the lowest possible yrast, quasi-beta, quasi-gamma bands, producing both the level structure of these bands and related B(E2) values in reasonable consistency with experiment. These trial calculations suggest that with our PCV approach the NPA can be meaningfully applied to transitional nuclei with a wide spectrum of shapes. We also show that while neutron negative-parity pairs could in principle have an important impact on backbending in $^{132}$Ba, they are not favored for this nucleus.

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