基于HIRFL-CSR的类氦重离子2E1双光子跃迁实验研究

According to the theoretical prediction, relativistic effects on the two-photon spectral shape are the most pronounced in heavy highly-charged ions. Therefore it would be of particular advantage to perform measurement of the two-photon decay in such systems. A novel experimental approach for studying two-photon decay in He-like high-Z ions will be developed relying on HIRFL-CSR and its internal target facility. In this technique, excited He-like heavy ions will be formed by K-shell ionization of initially Li-like ions in the collisions with a low-Z gas target, and x-ray spectra from the decay of the He-like ions were measured coincident with up-charged ion measurements. The very high level of selectivity of the system makes this process particularly suited for the study of the two-photon energy distribution, and thus for a detailed investigation of the structure of high-Z He-like atoms. The method allowed for a background-free measurement of the two photon decay. The experimental study will be very helpful for investigating reletivistic effects, electron correlation, and QED.

双光子跃迁能谱的形状能够细致反映原子内部结构和跃迁方式；针对现有的2E1双光子跃迁能谱测量技术的局限，依托兰州重离子加速器冷却储存环和气体内靶装置，高选择性地产生特定激发态类氦重离子，结合内靶实验的低本底和离子-光子符合技术的高效率，大幅度地提高能谱测量的精度和效率，细致测量激发态类氦重离子的双光子跃迁能谱（尤其是两翼能谱），以检验相对论条件下的理论预言，探索相对论效应、电子关联效应、甚至强库仑场QED效应对原子内部结构及其跃迁方式的影响。

相对论效应、电子-电子关联效应及库仑场QED效应对多激发态重离子的内部结构与退激属性有着重要影响。本项目依托兰州重离子加速器冷却储存环和气体内靶装置，研制了一台下游离子气体探测器，基于VME插件搭建了一套多路光子-离子符合电子学，编写了MIDAS框架下的数据获取程序，发展了基于储存环内靶谱学终端的双光子跃迁实验技术。以95 MeV/u、268 MeV/u镍离子与氩、氪、氙等气体靶碰撞，通过测量离子发射的X射线谱及角度分布信息，结合基于Dirac-Fock-Sturm轨道的相对论耦合道方法、相对论多组态Dirac-Fock理论及蒙特卡罗方法，研究了相对论能区不同扰动程度下多激发态镍离子的产生动力学与退激机制。测量了180度夹角下207Bi放射源的双光子符合谱。项目执行期间，已发表国外SCI期刊论文一篇，国内SCI期刊论文一篇；毕业一名博士生、一名硕士生。实验数据的系统分析尚未完成，物理结果将在今后陆续发表。