<sup>129</sup>Xe<sup><i>q</i>+</sup> induced near-infrared light and X-ray emission at Cu surface

Abstract

During the interaction of highly charged ions with solid target in the energy region near the Bohr velocity, the potential energy of the projectiles will be deposited on a nanometer-scale target surface within the time on the order of femtoseconds. That will lead the target atoms to be ionized into ions and the ions to be excited, resulting in the multiple ionization states and the complex configuration of energy levels. The de-excitation radiations of these levels cover the radiations from near-infrared spectral line to X-ray. Investigation of these spectral lines is significant for investigating the mechanism of such an interaction, diagnosing plasma and studying astrophysics. The experimental results show that the near-infrared spectral lines and X-ray spectra are produced by the <sup>129</sup>Xe<i><sup>q</sup></i><sup>+</sup> (<i>q</i> = 21, 23, 25, 27) with kinetic energy of 1360 keV and <sup>129</sup>Xe<sup>20+</sup> with kinetic energy of 4 MeV impacting on the Cu surface, separately. The experiment is carried out in the National Laboratory of Heavy Ion Research Facility in Lanzhou, HIRFL. The beam intensity is on the order of nA. The highly charged ions capture the electrons of the Cu target and thus being neutralized in a femtosecond time. The energy of the highly charged ions is deposited on the target surface, and the target atoms are excited or ionized, resulting in the transition between complex configurations, such as the dipole forbidden transition (magnetic dipole and quadrupole transition) and magnetic dipole transition of the Cu<sup>22+</sup>. The infrared spectral lines of the atoms and ions from deexcitation radiation are measured. With the 4 MeV <sup>129</sup>Xe<sup>20+ </sup>ions impacting on solid Cu surfsce, the X-rays are measured, such as, the magnetic dipole deexcitation radiation transition of Cu<sup>22+</sup>, the X-rays of the L<sub>1</sub> edge transition and L<sub><i>β</i>3</sub> of the Cu I, L<i><sub>η</sub></i> and L<sub><i>β</i>3</sub> X-rays of the Xe ions. The results show that during the neutrilization of highly charged Xe ions with lower energy above the Cu surface, the infrared lines are mainly from the deexcitation of the incident ions and the ionized or excited target atoms. The increasing trend of the the single ion fluorescence yield of the infrared spectral line is the same as that of the potential energy of the projectile. The characteristic L X-rays of the Xe atom are emitted by the second generation of hollow atoms formed below the surface.