质子滴线核27S及其附近核素衰变性质的实验研究

The drip-line nuclides have exotic structures and complicated decay processes in comparison with the stable nuclides. The investigation of the decay properties close to the drip line deepens our understanding of the nuclear structure and astrophysical nucleosynthesis. The isotopes of interest will be provided by the RIBLL1 facility at the Heavy Ion Research Facility of Lanzhou and a detection system composed of silicon detectors and preamplifiers will be developed on our own. The complicated decay schemes of nuclides around 27S can be reconstructed by measuring the emitted γ rays and particles in the decay with high efficiency and high energy resolution detection setup, which was designed to extract reliable information about the very rare decay events from disturbances on the bases of the our previous studies. This project aims at: (1) Conducting precise spectroscopic studies of 27S and 26P, thus providing spectroscopic inputs for constraining the uncertainties for reactions within the MgAl circle in nova nucleosynthesis. (2) Clarifying a possible mirror asymmetry for the mirror decays of 27S and 27Na, and exploring the relationship between isospin symmetry breaking and weakly-bound halo structure with shell-model calculations. (3) Achieving complete-kinematic measurements of the angular and energy correlation of β-delayed two-proton emission from 27S, which can give us more information about the mechanism of two-proton emission. β-decay spectroscopy will provide essential data for the understanding of the nucleosynthesis processes, the stringent test of fundamental interactions, and the theoretical description of weakly-bound nuclei.

远离稳定线原子核具有与稳定核显著不同的奇特结构与复杂衰变过程，在核结构与核天体两方面都具有重要的研究意义。本项目计划依托兰州重离子加速器大科学装置RIBLL1谱仪产生所需放射性核素，自主研发硅探测器阵列及前端电子学系统，配合高纯锗探测器精确测量27S及附近滴线核素衰变产生的带电粒子和γ射线，鉴别各种复杂衰变道以构建完整衰变纲图。主要实现：(1)通过β衰变布居27P,26Si等核的激发态，测量影响星际26Al丰度的天体核过程关键共振态性质；(2)澄清27S与27Na镜像衰变是否存在非对称性的争议，结合壳模型理论和镜像核结构分析同位旋对称性破缺与晕结构的关系；(3)实现27S的β延迟双质子发射能量与角度关联的运动学完全测量，深入研究双质子发射物理机制。本项目研究将为天体核合成网络计算、严格检验各种有效相互作用、发展弱束缚核相关理论模型提供关键数据。

β衰变谱学为新星与X射线暴天体模型计算提供关键输入量，也是检验远离稳定线壳模型理论可靠性的重要工具。本项目将一系列质子滴线核素注入双面硅条探测器，外围匹配高纯锗探测器，精确测量了27S和26P附近核素衰变产生的带电粒子和γ射线，鉴别各种复杂衰变道构建了完整的衰变纲图。研究发现：1）26Si(p,γ)27P热核反应率在温度0.1 GK附近比天体数据库推荐值低两个数量级。 25Al(p,γ)26Si反应率得到进一步确认。基于新实验数据提取质量及反应率，代入新星天体模型计算，发现新星爆发对星际26Al丰度的贡献无明显改变，确认了之前的新星模型灵敏性研究结论。而将我们的质量及反应率代入X射线暴天体模型计算，发现能够使X射线暴过程中26Al产额增至采用AME2016推荐质量值时产额的2.4倍，能量产生率和光变曲线无明显改变。此外，代入27S新质量的计算结果使得先前认为27S是等待点核的这个结论不再成立。2）我们将此次实验数据与壳模型理论计算和镜像核27Na衰变结果进行了对比，发现考虑质子s1/2轨道弱束缚效应的壳模型理论可以很好地解释实验数据，加深了对奇特核结构的理解。3）我们还开展了双质子角关联研究，将实验数据与Monte Carlo模拟结果进行比对，发现27S β2p的主要发射机制为级联发射。