Quasimolecular inner-shell charge-transfer cross sections for light projectiles in solids

Abstract

$K$-shell vacancy fractions have been measured for B, C, N, O, and Ar projectiles traversing thin carbon foils. The equilibrium vacancy fractions were determined by measuring Auger electron yields from the projectiles emerging from the foils. Projectile energies ranged from 50 to 500 keV. The fractions increase as energy increases, up to saturation values. The measurements are interpreted in terms of vacancy creation and filling events, using previously measured cross sections and vacancy sharing ratios. Collisional vacancy filling cross sections for projectile-carbon atom collisions are extracted, and the mechanisms responsible for saturation are delineated. These cross sections are compared to available theoretical estimates and are found to be much larger than those predicted by modified Brinkman-Kramers theory. This is attributed to quasimolecule-formation effects. Tentative values for dynamical projectile vacancy lifetimes are obtained.