Characteristic X-Ray Production in Magnesium, Aluminum, and Copper by Low-Energy Hydrogen and Helium Ions

Comparative characteristic $K$ x-ray yields in Mg and Al and, $L$ x-ray yields in Cu, produced by bombardment with singly charged ions of H, ${\mathrm{He}}^3$, and ${\mathrm{He}}^4$, are reported for particle energies ranging from 25 to 50 keV per amu. Characteristic x-ray production cross sections for the $K$-shell processes are extracted from these data, and from previous proton work. The ratios of helium to proton cross sections at equal particle velocities are significantly smaller than expected from current theories. It is shown that the discrepancy can be fully accounted for by the effect on the cross section of the binding of the $K$-shell electrons to the projectile, which is in close proximity to the nucleus at the time of excitation.