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 ca lculated 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 t akes into account distortion effects due to the long-range Coulomb pot ential. From the cross sections for the different reaction channels we obtain the equilibrium charge-state fractions, the electronic stoppin g power associated with each reaction channel, and the mean electronic stopping power. This information allows a detailed study of the veloc ity dependence at low impact velocities.