One of characteristic phenomena for nuclei beyond the proton dripline is the simultaneous emission of two protons (2p). The current status of our knowledge of this most recently observed and the least known decay mode is presented. First, different approaches to theoretical description of this process, ranging from effective approximations to advanced three-body models are overviewed. Then, after a brief survey of main experimental methods to produce 2p-emitting nuclei and techniques to study their decays, experimental findings in this research field are presented and discussed. This review covers decays of short-lived resonances and excited states of unbound nuclei as well as longer-lived, ground-state radioactive decays. In addition, more exotic decays like three- and four-proton emission are addressed. Finally, related few-body topics, like two-neutron and four-neutron radioactivity, and the problem of the tetraneutron are shortly discussed.

超出质子滴线的核的特征现象之一是同时发射两个质子 (2 p )。介绍了我们对这种最近观察到的和最不为人知的衰变模式的了解现状。首先，概述了从有效近似到高级三体模型的不同理论描述该过程的方法。然后，在对主要实验方法进行简要调查后，产生 2 p-发射核和研究其衰变的技术，介绍和讨论了该研究领域的实验结果。这篇综述涵盖了未结合原子核的短寿命共振和激发态的衰变，以及寿命更长的基态放射性衰变。此外，还解决了更奇特的衰变，如三质子和四质子发射。最后，简短地讨论了相关的少体主题，如双中子和四中子的放射性，以及四中子的问题。