不稳定原子核β衰变强度的实验测量方法

Experimental Measurement Method of Beta Decay Strength of Unstable Nuclei

原子核的β衰变是指原子核放射出β粒子或俘获电子而进行的转变。对β衰变强度Sβ(E)的精确测量,对探索不稳定原子核的结构、揭秘恒星核合成过程、验证β衰变理论等方面均存在着重要意义。实验上,为了测量β衰变强度,一种方法是利用β-γ符合测量或者全吸收谱仪对β衰变产物进行直接测量,这种方法可以给出子核在Qβ窗口内的衰变信息。另一种方法是利用在中等能区(100~400 MeV/u)进行的电荷交换反应,如(p,n)或(^(3)He,t),通过微分截面的高精度测量获得子核的β衰变强度,这种方法可以用于研究子核在Qβ窗外的衰变强度,但是对束流强度有较高的要求,尚无法系统研究产额较低的不稳定原子核。有鉴于此,本文提出对不稳定核素的电荷交换反应总截面进行系统测量,结合核反应理论,这种方法有望约束不稳定核素在质子发射阈下的Gamow-Teller跃迁的总强度。最后简要介绍了已开展和计划开展的工作。

The β decays of atomic nuclei refer to the transformation that the nuclei emit a β particle or capture an electron.The accurate measurements of the β transition strength functions Sβ(E) are of great significance in exploring the structure of unstable nuclei,revealing the process of stellar nucleosynthesis and also verifying the β decay theories.Experimentally,one way to determine the β transition strength is to directly measure the beta decay product using β-γ coincidence technique and/or total absorption spectroscopy.This method can give the transition information within the Qβ window.Another method to obtain the β decay strength is via the charge exchange reactions performed at the intermediate energy region(100~400 MeV/u),such as(p,n) or(^(3)He,t).This is done by a high-precision measurement of the differential cross section.This method allows to access the transition strength that beyond the Qβ window,however,it is restricted by the beam intensity,and as a consequence hard to perform a systematical study of unstable nucleus with low yields.In view of this,in this paper we proposes a systematic measurement of the total charge exchange reaction cross section of the unstable nuclei.Combined with the well developed nuclear reaction theory,this method may set a constrain to the summed strength of the Gamow-Teller transition of the unstable nuclei within the proton separation threshold.Moreover,we introduce briefly the relevant work that has been carried out and planned.