原子核是由质子和中子构成的复杂量子多体系统。质子-中子相互作用在原子核壳结构演化和集体性质演化方面起重要作用。质子-中子配对关联对 N=Z 原子核的结构十分重要。近年来同位旋标量的质子-中子配对关联是原子核结构理论和实验研究中的重要前沿问题，在国际上许多重要的核物理实验室把同位旋标量的配对关联作为很高优先级的物理目标。随着放射性核束装置的飞速发展，人们能够测量质子滴线附近质量数约为100的原子核的基态和低激发态性质，这为研究不稳定缺中子原子核中的质子-中子相互作用以及 N=Z 原子核中的质子-中子配对提供了很好的机遇。本项目计划利用壳模型的配对近似理论研究以下问题，着重研究原子核中的质子-中子关联：（1）质子-中子单极相互作用与偶偶Sn同位素链中 Z=50 壳能隙的演化；（2）质子-中子配对与 N=Z 原子核的 Wigner 效应、同位旋反转；（3）质子-中子相互作用奇偶性的微观机制。

Atomic nuclei are complex quantum many-body systems consisting of protons and neutrons. Proton-neutron interaction plays an important role in the evolution of nuclear shell structure as well as in the development of nuclear collectivity. Proton-neutron pairing correlation is of great importance to the structure of N=Z nuclei. In recent years the issue of isoscalar proton-neutron pairing correlation has attracted much attention of both theoreticians and experimentalists, and is among the high priorities in many famous laboratories of nuclear physics in the world. With the rapid development of radioactive beam facility, properties of the ground and low-lying states in nuclei near the proton drip-line with mass number around 100 become accessible. This provides us with great opportunity to study proton-neutron interaction in unstable neutron-deficient nuclei and proton-neutron pairing correlation in N=Z nuclei. In this project we shall study the following issues in the framework of nucleon-pair approximation of the shell model, with our focus on proton-neutron correlation: (1) the role played by monopole proton-neutron interaction in the evolution of the Z=50 shell in even-even Sn isotopes, (2) proton-neutron pairing correlation, and its relation with the Wigner effect and the isospin inversion in N=Z nuclei, and (3) microscopic mechanism of the odd-even staggering in proton-neutron interaction.