Secondary Electron Emissions from Metal Surface by High-Energy Ion and Neutral Atom Bombardments

To obtain γₑ for H₂⁺ ion bombardment on metal targets, an expression for the secondary electron emission coefficient by fast positive ion bombardment is obtained after adopting a method of calculation similar to that employed by Sternglass. It is shown that the experimental values of γₑ for H₂⁺ ion bombardment agree with the calculated values provided it is assumed that inside the target a hydrogen molecular ion is dissociated into a proton and a hydrogen atom, each having half the energy of the molecular ion. The dissociation cross section of a hydrogen molecular ion inside the target may be given by σd=KT, where $K=1.2$, σd is expressed in units of 10^-17 cm², and T is in Mev.The secondary electron emission coefficient γₑ for high-energy hydrogen atom bombardment on a metal surface is also calculated and compared with experimental data. In the calculation, a neutral beam of hydrogen atoms is treated inside the target as composed of protons and electrons in addition to hydrogen atoms. Each of these three kinds of particles are capable of producing internal secondaries.A fair agreement between the calculated and observed values of γₑ for H⁺, D⁺, H₂⁺, and H⁰ bombardments has been obtained.