Exotic nuclei and nuclear forces
Exotic nuclei and nuclear forces
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DOI：
10.1088/0031-8949/2013/t152/014007
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发表时间：
2013
期刊：
影响因子：
2.9
通讯作者：
T. Otsuka
中科院分区：
文献类型：
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作者：
T. Otsuka
我概述了与稳定核相比，外来核结构的新方面，重点是核力的几个特征效应。原子核的壳层结构是由Mayer和Jensen提出的，并且被认为基本上对所有的原子核都有效，具有著名的幻数，2,8,20,28,50,....最近，核力量被证明改变了这种模式。随着中子和/或质子的增加，壳层结构的演变将以各种方式发生，我将根据核力的单极相互作用提出这种壳层演变的基本要点。我将讨论三种核力量。第一个是张量力。张量力是最基本的核力之一，但它对壳层结构的一阶作用直到最近才在外来核的研究中得到阐明。张量力可以改变自旋轨道分裂，这取决于特定轨道的占用。这导致许多原子核的壳层结构发生变化，因此在某些原子核中，一些迈尔-延森神奇数丢失，而新的神奇数出现。这种机制可以用一种直观的方式来理解，这意味着它的效果是通用的和健壮的。第二种核力是中心力。我将在壳模型哈密顿量中展示中心力的一个一般但未知的性质，它可以很好地描述与实验一致的核性质。然后，我将演示如何将其合并到一个简单的中心力模型中，并将讨论这种力在壳演化中的作用。实际上，通过将这个中心力与张量力结合起来，人们可以理解和预见相同的质子-中子相互作用是如何驱动壳层演化的，例如Sn/Sb同位素、N = 20原子核和Ni/Cu同位素。并与48Ca上的（e,e 'p）实验进行了对比，讨论了单粒子强度的分布。壳层演化通过jahn - teller机制影响核的形状，并讨论了一个非常有趣的外来Si同位素的例子。第三种核力是三体力，起源于多年前Fujita和Miyazawa提出的Δ粒子激发。这种力被证明在从核心的第三个核子的效应平均后，在价中子之间产生排斥相互作用。同样的三体力也是中子星形成的原因。例如，通过考虑三体力的这种影响，人们可以预测氧同位素的正确滴注线。因此，由于特定的核力，原子核的景观在从稳定到奇异的原子核中变化，导致了范式的转变。本文概述了一些基本思想和选择的例子。
I overview new aspects of the structure of exotic nuclei as compared to stable nuclei, focusing on several characteristic effects of nuclear forces. The shell structure of nuclei has been proposed by Mayer and Jensen, and has been considered to be kept valid basically for all nuclei, with well-known magic numbers, 2, 8, 20, 28, 50, …. Nuclear forces were shown, very recently, to change this paradigm. It will be presented that the evolution of shell structure occurs in various ways as more neutrons and/or protons are added, and I will present basic points of this shell evolution in terms of the monopole interaction of nuclear forces. I will discuss three types of nuclear forces. The first one is the tensor force. The tensor force is one of the most fundamental nuclear forces, but its first-order effect on the shell structure has been clarified only recently in studies on exotic nuclei. The tensor force can change the spin–orbit splitting depending on the occupation of specific orbits. This results in changes of the shell structure in many nuclei, and consequently some of Mayer–Jensen's magic numbers are lost and new ones emerge, in certain nuclei. This mechanism can be understood in an intuitive way, meaning that the effect is general and robust. The second type of nuclear forces is central force. I will show a general but unknown property of the central force in the shell-model Hamiltonian that can describe nuclear properties in a good agreement with experiment. I will then demonstrate how it can be incorporated into a simple model of the central force, and will discuss how this force works in the shell evolution. Actually, by combining this central force with the tensor force, one can understand and foresee how the same proton–neutron interaction drives the shell evolution, for examples such as Sn/Sb isotopes, N = 20 nuclei and Ni/Cu isotopes. The distribution of single-particle strength is discussed also in comparison to (e,e′p) experiment on 48Ca. The shell evolution affects shapes of nuclei through Jahn–Teller-type mechanism, and a very interesting example with exotic Si isotopes is discussed. The third type of nuclear force is a three-body force, which originates in the Δ particle excitation as proposed by Fujita and Miyazawa many years ago. This force is shown to produce a repulsive interaction between valence neutrons after averaging effects from the third nucleon in the core. The same three-body force is responsible for neutron stars. By including such effects of the three-body force, one can predict the correct drip line of oxygen isotopes, for instance. Thus, the landscape of atomic nuclei varies in going from stable to exotic nuclei due to particular nuclear forces, leading to a paradigm shift. This paper overviews some basic ideas and selected examples.