BackgroundThe highly charged nitrogen ions (Nq+, q=3, 5, 6) are one of the main charged ions in the solar wind. Study of K-shell X-ray emissions in collisions of Nq+ (q=3, 5, 6) ions with a Cu surface is of great significance for understanding the de-excitation process of "hollow atoms" and the generation mechanism of comet X-rays.PurposeThis study aims to investigate characteristics of K-shell X-ray emission in impacts of Nq+ (q=3, 5, 6) ions with a Cu surface.MethodsThe Nq+ (q=3, 5, 6) ion beam was generated by the electron cyclotron resonance ion source (ECRIS) in Institute of Modern Physics, Chinese Academy of Sciences. The K-shell X-ray spectra resulted from collisions of the Nq+ ions with the Cu surface were acquired by a silicon drift detector (SDD). Based on the X-ray spectra, K-shell X-ray yields and ionization cross sections were calculated.ResultsThe results show that, for the Nq+ (q=3, 5) ion incidence, K-shell X-ray emissions are attributed to close collisions of the ions with Cu atoms on the subsurface of the target, and that the K-shell X-ray yields and ionization cross sections increase monotonically with the increase of kinetic energy of the incident ions. For the N6+ ion incidence, the K-shell X-ray yields have no obvious dependence on kinetic energy of the incident ions. The K-shell X-rays are primarily emitted from the above-surface of Cu target through the de-exciting of the formed "hollow N atoms", and they account for about 97% of the total X-rays. In addition, the X-ray yield of the N5+ ion incidence is higher than that of N3+ ions.ConclusionsThis study provides basic data for the understanding the de-excitation process of "hollow atoms" and the generation mechanism of comet X-rays.
