摘要
放射性是不稳定核的一个重要特性,比较常见的模式有α、β、γ衰变及裂变.双质子发射是质子滴线区原子核的一种奇异放射性,对研究极端丰质子核的结构、质量、质子对关联等有重要意义,是近年来放射性核束物理的重要前沿方向之一.本文简要评述了双质子发射实验研究进展,介绍了几种常用的实验探测方法及鉴别双质子发射机制的研究方法.奇异放射性研究的困难在于滴线区不稳定核的产生.中国在建的HIAF装置有强流的优势,结合先进的探测技术与研究方法,将来有望在滴线区原子核的奇异放射性实验研究方向开展最前沿的工作.
Radioactivity is one of the most significant characteristics of unstable nuclei, the familiar modes including α, β, γ decay and fission. Two-proton(2p) emission is an exotic radioactivity mode of nuclei in the proton drip-line area, which is very significant for studying the structure, mass and correlation between proton pair of extremely proton-rich nuclei and one of the frontiers in radioactive ion beam physics. In this article, progress of experimental studies on two-proton emission was briefly reviewed. Several experimental measurement methods were introduced. The identification method for the mechanism of two-proton emission was discussed. Two-proton emission was predicted to be existed in extremely protonrich nuclei in 1960. For 2p emission from the ground state of a nucleus with long half-life, it was observed for the first time in 2002 due to the difficulty in the production of a candidate. Only few decay events were observed for the four proton dripline nuclei with a long half-life ground state. For the detection of 2p emission process, the in-flight decay, implantation decay and optical time projection chamber(OTPC) plus CCD method are the three main experimental methods. The inflight decay method is suitable for the candidate with very short half-life and almost inapplicable for the candidate with a half-life longer than 1 μs. The implantation decay method is suitable for the candidate with long half-life, especially for β-delayed decay nuclei. In this case, the measured decay signal will be very clear with low background due to the separation recording of the implantation and decay events. The OTPC plus CCD method could record a picture of 2p emission process directly for the candidate. Generally, there are three mechanisms for proton-rich nuclei to emit two protons:(1)2He cluster emission;(2) three-body emission;(3) sequential emission. The 2He cluster emission is basically two protons constrained by the pair correlation into a quasi-bound singlet, i.e.,1S0 configuration. Such a quasi-bound state can only exist for very short time and then becomes separated after penetrating through the Coulomb barrier. Usually, the two-proton relative momentum and the opening angle distributions are used to identify the mechanism of 2p emission in experimental investigations. However, this method can only distinguish it being 2He cluster emission or not. For the three-body and sequential emissions, the key difference is the emission time between the two protons. The proton-proton momentum correlation function(also called HBT) method is a widely used analysis technique in nuclear physics, which can extract the emission time of a particle. It has been demonstrated that the three-body and sequential emissions could be distinguished by using the HBT method. The difficulty in the study of exotic radioactivity is the low production rate of the unstable nuclei in the drip-line area. The high-intensity heavy-ion accelerator facility(HIAF) under construction in China has an advantage of high beam intensity, the most frontier work in the field of exotic radioactivity for nuclei around the drip-line could be performed on it by adopting the superior detection technique and investigation method.
作者
方德清
马余刚
Deqing Fang;Yugang Ma(Key Laboratory of Nuclear Physics and Ion-beam Application of Ministry of Education,Institute of Modern Physics,Fudan University,Shanghai 200433,China)
出处
《科学通报》
EI
CAS
CSCD
北大核心
2020年第35期4018-4026,共9页
Chinese Science Bulletin
基金
国家重点研发计划(2018YFA0404404)
国家自然科学基金(11925502,11935001,11961141003,11421505,11475244,11927901)
上海市自然科学基金(19ZR1403100)
中国科学院B类战略性先导科技专项(XDB34030100)资助。
关键词
丰质子核
双质子发射
在束衰变方法
注入衰变方法
光学读出时间投影室成像方法
proton-rich nuclei
two-proton emission
in-flight decay method
implantation decay method
optical time projection chamber-CCD method
