Electron detachment cross-sections in low energy heavy negative ion beam appratus

Abstract

We have measured the single- and double-electron detachment cross-sections of B, C, O, and Si negative ions on He, Ar, Xe, H 2 and N 2 gas targets in an ion beam energy range of 5–50 keV. The single-electron detachment cross-section in this energy range is nearly constant and around 10 − 15 cm 2 , while the double-electron detachment cross-section increases in proportion to the ion velocity and is much smaller in area than the single one. The order of magnitude of both cross-sections for negative ion species is Si - > B - > C - > O -. The order for target gases is Xe > Ar > He for single atomic gases and N 2 > H 2 for molecular gases. These properties can be quantitatively explained by considering the orbital radius of the electrons in the outermost shell of the negative ion, the number of electrons, the electron affinity (for single-electron detachment), the sum of the electron affinity and first ionization potential (for double-electron detachment) and the atomic radius of the target gas.