K -shell ionization of 25–100 keV N q + ( q = 3, 5) ions impinging on Al and Cu surfaces

In this paper, K -shell X-ray spectra of nitrogen are measured by the interaction of N q + ( q = 3, 5) ions with Al and Cu surfaces in the impact energy range of 25–100 keV. K-shell X-ray yields per incident ion and then ionization cross sections are deduced from the measured K-X-ray spectra. It is found that both the yields and cross sections increase quickly with increasing impact energy, but have no apparent dependence on the target material and the charge state of the incident ion. The experimental results reveal that the incident N q + ( q = 3, 5) ions have been neutralized and achieved a charge-state equilibration before the K -shell electron is ionized. The experimental ionization cross sections are compared with those from the plane wave Born approximation (PWBA) and the classical binary encounter approximation (BEA) theory. The BEA calculations are better consistent with the experimental data than the PWBA. It means that the K -shell ionization of the incident N q + ( q = 3, 5) ions is due to the direct Coulomb excitation processes that occurred below the target surface. Graphic abstract K-shell ionization cross sections of N q + ions incident on an Al target. The theoretical calculations of BEA and PWBA models are also shown for comparison