Electron-capture contribution to the stopping power of low-energy hydrogen beams passing through helium

The energy loss of hydrogen beams traversing a helium gas target is calculated using the charge-state approach. The first Born approximation is used for the neutral charge-state and the continuum-distorted-wave--eikonal-initial-state model for the proton charge state. This model takes into account distortion effects due to the long-range Coulomb potential. From the cross sections for the different reaction channels we obtain the equilibrium charge-state fractions, the electronic stopping power associated with each reaction channel, and the mean electronic stopping power. This information allows a detailed study of the velocity dependence at low impact velocities.