丰质子区N=126附近核素衰变性质研究

Studying super-heavy nuclei and searching the island of stability have been one of the frontiers of nuclear physics research for a very long time. The proton and neutron numbers of the nuclides on the island are believed to be close to the next magic numbers, which different theoretical models give different predictions. Therefore, these models have to be constrained and tested extensively by information from experiments. Some hints may be given by the studies on the exotic nuclides far from the beta stability valley with known proton and neutron magic numbers. From our previous studies on the decays of proton-rich even-even nuclides near the N=126 neutron shell, we already found that the decay pattern of new observed extremely proton-rich nuclides 216U and 218U are different from other isotopes nearby and it may indicate that the N=126 neutron shell has already influenced differently the structures and decays of the U isotopes. This project will try to synthesize new isotope 214U and study the decays from 216U, 214U and the Np and Pu isotopes near the N=126 neutron shell and their decay patterns in details. The products of interest will be separated by advanced gas-filled recoil separator and transported to the detection chamber where the decays from nuclides will be detected by our fast data acquisition system. By using position-time correlation measurement method and single-atom sensitive identification technology, detailed and reliable information about the isotopes in this region can be extracted and used to test predictions of the next magic numbers.

超重核研究及超重稳定岛的寻找一直是核物理研究的前沿之一。下一个中子及质子幻数很可能是超重稳定岛的具体位置，但目前不同的理论模型预言的位置各不相同，因此需要大量的实验数据对模型进行约束和进一步的检验。通过研究已知的中子、质子幻数在远离β稳定线奇特核中的影响可以提供一些线索。在研究丰质子区N=126附近的偶偶核的衰变规律时，我们发现最新观测到的极端丰质子核U216与U218的衰变与其它核素衰变的规律存在不同，该现象可能表明N=126中子壳的影响在U附近已经发生了变化。本申请的主要内容就是合成新核素214U及Np、Pu在N=126附近核素，并研究其衰变，并详细研究U216、U218结构，观测这些衰变的变化情况。实验将使用充气反冲谱仪等先进的分离传输装置和快速数据获取系统，通过位置时间关联测量方法，利用单原子鉴别技术，得到该区域核素详实、可靠的实验数据，为下一幻数的预言提供数据支持。

基于中国科学院近代物理研究所加速器国家实验室的充气反冲谱仪平台，使用36Ar、40Ar及40Ca等束流轰击180W、182W、184W、187Re等靶，围绕N=126中子壳附近的核素进行了研究，特别是针对中子壳126附近的铀同位素进行了研究。仔细研究218U、216U的衰变情况；对219U及218Pa的结构进行了研究；并首次合成了214U、222Np及220Np，测量了它们的衰变。