Target-atomic-number-dependent oscillations of equilibrium charge-state distributions of 50–500-keV/u hydrogen and boron emerging from solids

The target dependence of equilibrium charge-state distributions was studied for medium-energy (50–500-keV/u) hydrogen and boron emerging from solids. Using a backscattering method, charge fractions were measured for various elemental solid substances with atomically clean surfaces in a pressure range of ${10}^{\mathrm{-}8}$ Pa. The respective charge fractions of hydrogen and boron are found to oscillate with target atomic number ${\mathit{Z}}_{\mathit{t}}$, reflecting the periodic electron shell structures of the target atoms. Comparison between the ${\mathit{Z}}_{\mathit{t}}$ oscillations of hydrogen and boron revealed that the oscillatory behavior depends on the final bound state of the captured electrons. This oscillatory behavior can reasonably be explained by the Oppenheimer-Brinkman-Kramers approximation.