Microscopic Nuclear Structure Theory

微观核结构理论

• 批准号: 0244389
• 负责人: Bruce Barrett
• 金额: $ 36.3万
• 依托单位: University of Arizona
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-06-01 至 2007-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0244389&HistoricalAwards=false
• 关键词: Microscopic; Nuclear; Structure; Theory

Tremendous progress has been made in the last ten years in calculating the properties of atomicnuclei microscopically starting with the free nucleon-nucleon (NN) interaction. One of the mostsuccessful theoretical approaches in this regard is the No Core Shell Model(NCSM). Insteadof invoking the standard shell-model assumption, that most of the nucleons occupy an inertcore, one treats all A nucleons as being active. In this way one is able to formulate a systematicprocedure to derive e.ective interactions starting from realistic microscopic ones. This proceduremakes use of the similar structures that two- and three-body clusters are expected to have in allnuclei. It was shown that these e.ective interactions speed up convergence tremendously andmake converged solutions possible.It has now become apparent that present theoretical techniques are able to accurately calculatethe properties of light nuclei using the NN interaction as input. Because the results showa considerable underbinding, it is clear that some extra ingredient is necessary, such as threenucleoninteractions. Hence, the NCSM will be expanded to include the three-body cluster (ore.ective interaction) based not only on the two-body microscopic forces, but also on realisticthree-nucleon (3N) bare interactions. It is important do this, because, for example, the spectraof light nuclei are expected to be sensitive to the spin structure of the 3N interaction. With thesehigher-body interactions one will also be able to perform NCSM calculations for heavier nucleiin smaller basis spaces and obtain better convergence and, hence, more accurate results. Thedevelopment of this three-body cluster approach is an major step forward, as it will enable oneto study the e.ects of current 3N interaction models and models based on chiral perturbationtheory on the spectra. Consequently, it will become an important tool to probe these interactions.By developing a technique for computing the three-body cluster exactly, one can alsoinvestigate its structure, depending upon the number of nucleons in the nuclide being studiedand upon the size of the model space.One of the goals of all nuclear structure calculations is the understanding of collective structuresbased on microscopic calculations. The structure of 12C is an interesting example. The.rst excited 0+ state is believed to have a 3a structure. Converged solutions for this problemare a challenge, but are within the reach of NCSM calculations. Once they can be obtained,one can study in detail the di.erence between the ground state and excited state structures.Another important aspect of the current investigations is the extension of the NCSM methods toarbitary operators. The NCSM is based on a unitary transformation of the cluster Hamiltonian.When one is able to extend this transformation to transition or current operators, it becomespossible to extract meaningful values for physical observables from the NCSM wave functions.The prediction of electroweak properties of light nuclei will be an important application of thisnew technique.

过去十年，从自由核子-核子 (NN) 相互作用开始，在微观计算原子核性质方面取得了巨大进展。这方面最成功的理论方法之一是无核壳模型（NCSM）。我们不采用标准的壳模型假设，即大多数核子占据惰性核，而是将所有 A 核子视为活跃核子。通过这种方式，人们能够制定一个系统的程序，从现实的微观相互作用开始推导出有效的相互作用。该过程利用了二体和三体簇在所有原子核中预期具有的相似结构。结果表明，这些有效的相互作用极大地加速了收敛速度，并使收敛解成为可能。现在已经很明显，现有的理论技术能够使用神经网络相互作用作为输入来准确计算轻核的性质。因为结果显示相当大的结合力不足，所以很明显需要一些额外的成分，例如三个核子相互作用。因此，NCSM 将扩展到包括三体簇（矿石相互作用），不仅基于二体微观力，而且还基于现实的三核子（3N）裸相互作用。这样做很重要，因为例如，轻核的光谱预计对 3N 相互作用的自旋结构敏感。通过这些更高体相互作用，人们还能够在较小的基础空间中对较重的核进行 NCSM 计算，并获得更好的收敛性，从而获得更准确的结果。这种三体簇方法的发展是向前迈出的重要一步，因为它将使人们能够研究当前的 3N 相互作用模型和基于手性微扰理论的模型对光谱的影响。因此，它将成为探测这些相互作用的重要工具。通过开发一种精确计算三体团簇的技术，人们还可以根据所研究的核素中的核子数量和模型空间的大小来研究其结构。所有核结构计算的目标之一是基于微观计算来理解集体结构。 12C的结构是一个有趣的例子。第一激发0+态被认为具有3a结构。这个问题的融合解决方案是一个挑战，但在 NCSM 计算的范围内。一旦获得它们，就可以详细研究基态和激发态结构之间的差异。当前研究的另一个重要方面是将NCSM方法扩展到任意算子。 NCSM 基于簇哈密顿量的酉变换。当人们能够将这种变换扩展到过渡算子或电流算子时，就可以从 NCSM 波函数中提取物理可观测量的有意义的值。轻核电弱性质的预测将是这项新技术的重要应用。