SHELL EFFECTS OBSERVED IN EXIT CHARGE-STATE DISTRIBUTIONS OF 1-30 KEV ATOMIC PROJECTILES TRANSITING ULTRATHIN CARBON FOILS

We have investigated the exit charge state distributions of 1-30 keV H, He, C, N, O, Ne and Ar ions that transit ultrathin carbon foils (average thickness of approximately 44 angstrom). The empirical charge state distributions are used to examine the ratio of the electron loss cross section sigma(l) for neutrals to the electron capture cross section sigma(c) for positive ions. The ratio, sigma(l)/sigma(c), is shown to have a quadratic dependence on the projectile velocity and inverse dependence on Z2/3 where Z is the projectile atomic number. The data is fit to the equation A(E(F) - E(T))/mZ2/3 where E(F) is the exit projectile energy, m is its mass, and A and E(T) are constants. A pronounced shell effect is observed: the constant A is dependent on the principal quantum number of the projectile, and E(T) exhibits variations with the projectile outer shell electronic structure.