Abstract This review paper concerns the research devoted to the study of the properties of dipole excitations in nuclei. The main focus is on questions related to isospin effects in these types of excitations. Particular attention is given to the experimental and theoretical efforts made to understand the nature and the specific structure of the low-lying dipole states known as the Pygmy Dipole Resonance (PDR). The main experimental methods employed in the study of the PDR are reviewed as well as the most interesting theoretical aspects. The main features of the experiments and of theoretical models are reported with special emphasis on the reaction cross sections populating the dipole states. Results are organized for nuclei according to different mass regions. The knowledge of the isovector dipole response as well as its low energy part is important in order to deduce the nuclear polarizability as accurate as possible. This issue is discussed in this paper together with the connection with the neutron skin and the nuclear equation of state. The important role played by the dipole response to deduce other physical quantities of general interest is discussed in the last two chapters. One concerns the level density and the other the isospin mixing in nuclei at finite temperature and its relation with beta decay.

中文翻译：

---

等标量和等向量偶极子激发：来自低位状态和等向量巨偶极子共振的核特性

摘要 这篇综述论文涉及致力于研究原子核中偶极子激发特性的研究。主要关注与这些类型激发中的同位旋效应相关的问题。特别关注为了解被称为侏儒偶极共振 (PDR) 的低位偶极态的性质和具体结构所做的实验和理论工作。回顾了 PDR 研究中采用的主要实验方法以及最有趣的理论方面。报告了实验和理论模型的主要特征，特别强调了填充偶极态的反应截面。根据不同的质量区域为原子核组织结果。等向量偶极子响应及其低能量部分的知识对于尽可能准确地推断核极化率很重要。本文将结合中子表皮和核状态方程的联系来讨论这个问题。在最后两章中讨论了偶极响应在推导其他普遍感兴趣的物理量方面发挥的重要作用。一个涉及能级密度，另一个涉及有限温度下原子核中的同位旋混合及其与β衰变的关系。在最后两章中讨论了偶极响应在推导其他普遍感兴趣的物理量方面发挥的重要作用。一个涉及能级密度，另一个涉及有限温度下原子核中的同位旋混合及其与β衰变的关系。在最后两章中讨论了偶极响应在推导其他普遍感兴趣的物理量方面发挥的重要作用。一个涉及能级密度，另一个涉及有限温度下原子核中的同位旋混合及其与β衰变的关系。