The x-ray spectra of hollow atoms

The x-ray spectra of hollow atoms in the interaction of highly charged argon ions with beryllium solid surface are reported. The interaction ions, provided by the electron cyclotron resonance (ECR) ion source in the National Laboratory of the Heavy Ion Research Facility in Lanzhou( HIRFL), include bare argon ions, which are produced by the ion source for the first time, and hydrogen-like, helium-like and lithium-like argon ions. We found that the K-shell x-ray yield of single particles in the interaction of hydrogen-like argon ions is 3.6 x 10(-3), which is 5 orders more than that of helium-like argon ions, and the K-shell x-ray cannot be measured in the interaction of lithium-like argon ions with beryllium surface.