ABSTRACT
The average energies ejected by He2+ impact at several hundred keVu-1 of ion energies are almost the same as those by proton impact (Bolorizadeh and Rudd 1986; Toburen and Wilson 1977). The similarity of average energies for ejected electrons suggested that the spectral difference between proton impact and α-particle impact is insigni‚cant. Toburen et al. (1980) showed the ratio of single differential cross sections (SDCSs) for electron emission for equal velocity protons and He2+ ions are distributed in the range 1.0 ± 0.2 for various projectile energies. As a ‚rst approximation, Rudd’s model of proton impact was applied to the SDCS for He2+ impact ionization (see Section 14.1). The SDCS for He++ was obtained by z2 scaling of proton data. For ion energies lower than 300 keVu-1, the model of Rudd reproduces well the experimental average energies of secondary electrons. As energy of He2+ increases, at energies greater than 300 keVu-1, the model underestimates the average energies up to ∼30% at 2 MeVu-1. To correct this discrepancy, calculated electron spectra were modi-‚ed to produce the average energies using suitable scaling factors.
