Coulomb deflection effects in ion-induced K-shell ionisation

Assuming a hyperbolic Kepler orbit for the projectile, an analytical expression for the monopole projectile path factor is derived in the semiclassical approximation. The case of an attractive potential is also included. An improved Bang-Hansteen deflection factor is found to be approximately valid for arbitrary electron wavefunctions. The method is applied to calculations of the monopole contribution to K-shell ionisation using relativistic electron wavefunctions.