X-ray emission produced by interaction of slow highly charged <inline-formula><tex-math id="Z-20210923142604">\begin{document}${\boldsymbol{ {\rm{O}}^{q+}}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210757_Z-20210923142604.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210757_Z-20210923142604.png"/></alternatives></inline-formula> ions with Al surfaces
Authors: Zhang Bing-Zhang , Song Zhang-Yong , Liu Xuan , Qian Cheng , Fang Xing , Shao Cao-Jie , Wang Wei , Liu Jun-Liang , Xu Jun-Kui , Feng Yong , Zhu Zhi-Chao , Guo Yan-Ling , Chen Lin , Sun Liang-Ting , Yang Zhi-Hu , Yu De-Yang ,   Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China,   School of Nuclear Science and Technology, University of South China, Hengyang 421001, China,   School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000, China,   School of Nuclear Science and Technology, University of Chinese Academy of Sciences, Beijing 100049, China
Published: September 2021

<sec>The interaction of highly charged ions with solid surfaces is a very complex multi-body process. When the ions are close to the solid surfaces, the potential energy of the ions will be deposited in a tiny area of the target surfaces in a short time and then emitting X rays, which has important scientific significance and application in Astrophysics and plasma diagnosis. For experiments on the interaction of highly charged ions with surfaces, not only the X-ray energy spectrum but also the X-ray yield should be measured accurately. The precise measurement of the X-ray yield depends on the ability to accurately measure the beam-current intensity. In the past, the beam-current intensity was acquired by measuring the target current. Since the interaction between highly charged ions and solids involves the emission of secondary electrons, the actual measured target current is the sum of the initial beam-current intensity and the intensity caused by the secondary electrons, resulting in inaccurate X-ray yield calculations. In this experiment, a new analytical device, beam-current density meter, has been designed, which can measure the beam-current intensity with an accuracy of 0.1 nA. By measuring the current on the density meter instead of the target current, the influence of secondary electrons is almost avoided, and a more accurate X-ray yield is obtained.</sec><sec>This paper reports the characteristic X-ray spectra of oxygen atoms emitted from the interaction of 1.5–20 keV/<i>q</i> highly charged <inline-formula><tex-math id="M13">\begin{document}${\rm{O}} ^{q+} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210757_M13.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210757_M13.png"/></alternatives></inline-formula> ions with aluminum surfaces. For the X rays emitted by <inline-formula><tex-math id="M14">\begin{document}$ {\rm{O}}^{q+} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210757_M14.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210757_M14.png"/></alternatives></inline-formula>(<i>q</i> = 3, 5, 6) ions, the experimental results show that it is due to the close collisions with aluminum atoms after entering the surfaces, while the X rays emitted by <inline-formula><tex-math id="M15">\begin{document}${\rm{O}} ^{7+} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210757_M15.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210757_M15.png"/></alternatives></inline-formula> ions mainly come from the decay of hollow atoms. Under the condition of equal kinetic energy, the X-ray yield of <inline-formula><tex-math id="M16">\begin{document}${\rm{O}} ^{7+} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210757_M16.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210757_M16.png"/></alternatives></inline-formula> ions with K-shell vacancy is about one order of magnitude higher than that of <inline-formula><tex-math id="M17">\begin{document}$ {\rm{O}}^{q+} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210757_M17.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210757_M17.png"/></alternatives></inline-formula>(<i>q</i> = 3, 5, 6) ions, and X-ray yield of <inline-formula><tex-math id="M18">\begin{document}$ {\rm{O}}^{6+} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210757_M18.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210757_M18.png"/></alternatives></inline-formula> ions without<i> </i>K-shell vacancy is also significantly higher than that of <inline-formula><tex-math id="M19">\begin{document}${\rm{O}} ^{3+} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210757_M19.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210757_M19.png"/></alternatives></inline-formula> and <inline-formula><tex-math id="M20">\begin{document}$ {\rm{O}}^{5+} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210757_M20.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210757_M20.png"/></alternatives></inline-formula> ions. Generally, the X-ray yield and ionization cross-section is associated with the initial electron configuration of incident ions, and increases with the growth of ions kinetic energy. Based on the semi-classical approximation theory of binary collision, we have estimated the kinetic energy threshold for the emission of the K<sub>α</sub>-X rays of <inline-formula><tex-math id="M22">\begin{document}$ {\rm{O}}^{q+} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210757_M22.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210757_M22.png"/></alternatives></inline-formula>(<i>q</i> = 3, 5, 6) ions as interacting with the aluminum target. As the incident kinetic energy is lower than the kinetic energy threshold, for <inline-formula><tex-math id="M23">\begin{document}${\rm{O}} ^{6+} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210757_M23.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210757_M23.png"/></alternatives></inline-formula> ions interacting with the sample, there may have a multi-electron excitation process that induces this K-electron ionization of the incident ions.</sec>