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(-8) Pa. The respective charge fractions of hydrogen and boron are found to oscillate with target atomic number Z(t), reflecting the periodic electron shell structures of the target atoms. Comparison between the Z(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.