I L-shell X-rays from near Bohr-velocity I20+ ions impacting on various targets

Abstract

The L-shell X-ray emissions of iodine are investigated as a function of target atomic number for 4.5-MeV I²⁰⁺ ions impacting on Fe, Co, Ni, Cu and Zn targets. Six distinct L-subshell X-rays are observed. The energy of the x-ray has a blue shift compared with the atomic data. The relative intensity ratio of Lβ_{1, 3, 4} and Lβ_{2, 15} to Lα_{1, 2} almost increase linearly with the target atomic number increasing. The ratio of I(Lι) to I(Lα_{1, 2}) and I (Lγ_{2, 3, 4, 4'}) to I(Lγ₁) are approximately proportional to the square of target atomic number. It is indicated that during the interaction of highly charged heavy ions with atom in the energy region near the Bohr velocity, the inner-shell process is mainly caused by the close-range collisions below the surface. There, the projectile not only has enough time to capture electrons from the target atom to be neutralized, but also has enough kinetic energy to ionize the inner-shell electron by coulomb interaction. At the balance between electron capture and ionization, the outer-shells of M, N, O etc. could be multiply ionized. The extent of multiple ionization increases with the target atomic number increasing. That leads to the energy shift, resulting in the change of the relative intensity ratio for the L-subshell X-ray. The smaller the atomic fluorescence, the larger the enhanced fluorescence caused by multiple ionization.