Hollow atoms are special atoms with multiple missing electrons in their inner shells, while their outer shells are still fully or partially filled with electrons. Studying the production mechanisms, internal structure, and de-excitation properties of these excited-state atoms provides insights into quantum electrodynamics and quantum many-body interactions, with applications in fields such as inner-shell ionization X-ray lasers, high-energy density physics, and molecular imaging.

Researchers at the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences recently confirmed that the fully stripped heavy ion-atom collision is an effective way to produce heavy hollow atoms in high yield. They have also developed a high-resolution planar crystal spectrometer to measure the fine structure of inner-shell multi-ionization ion X-rays. 

The results have been published in Spectrochimica Acta Part B: Atomic Spectroscopy and Physical Review A.

The efficient production and systematic study of heavy hollow atoms have long posed significant challenges. To address this challenge, the researchers conducted an experiment in which fully stripped xenon ions collided with xenon targets using the cooling storage ring at the Heavy Ion Research Facility in Lanzhou (HIRFL).

After measuring the X-ray spectra of the target atoms, the researchers found that the relative yield of hollow xenon atoms was up to 28.6% higher than that of K-shell single-vacancy xenon atoms. The result indicates that fully stripped heavy ion-atom collision is an effective method for the high-yield production of heavy hollow atoms.

To further investigate the generation and de-excitation characteristics of such hollow atoms, the researchers independently developed a compact, high-resolution, broadband planar crystal spectrometer. This spectrometer features a unique geometric configuration optimized for the X-ray spectral characteristics of multi-vacancy ions, significantly improving precision and convenience.

The newly developed spectrometer achieves a dynamic range of 0.53-19.3 keV and a single-exposure bandwidth of 0.04-6.58 keV within a compact space. Its energy spectral resolution exceeds 10² across the entire dynamic range. Using mosaic crystals increases its detection efficiency by more than 20 times compared to traditional planar crystal spectrometers.

These achievements lay a solid foundation for conducting relevant research at the Heavy Ion Research Facility in Lanzhou (HIRFL), the Low Energy high intensity heavy ion Accelerator Facility (LEAF), and the High Intensity Heavy-ion Accelerator Facility (HIAF).

This work was supported by the National Key R&D Program and the National Natural Science Foundation.

Figure 1. Kα satellite and hyper-satellite lines emitted by the hollow xenon atoms. (Image by IMP)

Figure 2. Structural diagram of the spectrometer (left) and typical test results (right). (Image by IMP)