Qi Guo

Probing Nuclear Excitation by Electron Capture in an Electron Beam Ion Trap with Non-destructive Isomer Detection via Precision Mass Spectrometry

Bingsheng Tu [1], Nan Xue [1,2,3], Jialin Liu [1], Qi Guo [1], Yuanbin Wu [4], Zuoye Liu [3,5], Adriana Pálffy, Yang Yang [1], Ke Yao [1], Baoren Wei [1], Yaming Zou [1], Xiangjin Kong [1,2], Yu-Gang Ma [1,2]

Abstract

Nuclear excitation by electron capture (NEEC) is an important nuclear excitation mechanism which still lacks conclusive experimental verification. This is primarily attributed to strong background x-/$γ$-ray noise and competing nuclear excitation processes which would overshadow the signals in various environments that NEEC takes place. Here, we propose an experimental approach to observe the NEEC process within a background-free environment. Through collisions with a highly-compressed mono-energetic electron beam in an electron beam ion trap, nuclei may get excited to a long-lived isomeric state via the NEEC process. Subsequently, ions can be extracted and Penning-trap mass spectrometry employed to unambiguously detect the isomer. Our study focuses on the promising candidate $^{189}\mathrm{Os}$, demonstrating measurable detection rates of the NEEC process and discussing the feasibility of the proposed approach. This new approach for observing the NEEC process may be realized in the near future.

Stepwise ionization of Mo$^{14+}$ ions in EBIT: The importance of the metastable level

Cunqiang Wu [1], Xiaobin Ding [1,2], Qi Guo [3], Ke Yao [3], Jialin Liu [3], Yunqing Fu [3], Chenzhong Dong [1,2]

Abstract

The visible spectrum of Mo$^{15+}$ ions was measured using a high-temperature superconducting electron-beam ion trap at the Shanghai EBIT Laboratory, with an electron beam energy $E_{e}$=400 eV, significantly lower than the ionization potential (IP=544.0 eV) of Mo$^{14+}$ ions in the ground state. To expound on the experiment, the energy level structure, radiative transition properties, electron-impact excitation, and electron-impact ionization cross section for both the ground state and low-lying excited state of the Mo$^{14+}$ ions were calculated using Dirac-Fock-Slater method with a local central potential and distorted wave approximation. The results demonstrated reasonable agreement with both available experimental and theoretical data. Through an analysis of the related atomic processes of Mo$^{14+}$ ion, a scenario involving the stepwise ionization of the metastable state 3p$^{6}$3d$^{9}$4s was proposed to explain the presence of the Mo$^{15+}$ ions with a lower energy of the incident electron. Finally, the significance of the metastable levels in ionizing Mo$^{14+}$ ions is highlighted.