Neutralization of 50-230-keV hydrogen ions which have penetrated Al, Au, C, and Cs films

The fraction of neutral atoms ${\Phi }_0$ in a beam of hydrogen projectiles (H,D; 50-230 keV) which have penetrated thin targets covering a wide range of atomic numbers and free-electron densities has been measured. Ordinary carbon, gold, and aluminum targets yield identical ${\Phi }_0$, in agreement with data already in the literature. However, pure gold, aluminum, or cesium evaporated in situ on the exit surface of a target foil yield a ${\Phi }_0$ dependent on the specific material at energies greater than 50 keV/amu. New information on ${\Phi }_0$ is obtained with solid cesium targets and on its dependence on the target tilt angle towards the beam direction. In the frame of a simple kinetic model ${\Phi }_0$ is dominated at low energies, 25-50 keV, by charge exchange in the electron blanket at the target surface. At high energies, >250 keV, ${\Phi }_0$ is determined by the atomic cross sections of charge exchange. Only in the intermediate-energy regime is ${\Phi }_0$ observed as dependent on the tilt angle of the target surface towards the beam direction.