Charge-state distributions of energetic 4He ions backscattered from Kr gas target

The energy dependence of the charge-state fractions of 4He ions backscattered at 90° from Kr gas target atoms was investigated for impact energies varying from 0.4 to 2.0 MeV. The fractions were measured using a small electrostatic post-accelerator system. The measured fractions were compared with previous literature results for backscattered 4He ions from solid targets, and with results for transmitted 4He ions through foils. It is observed that the charge-state distributions are strikingly identical for the Kr gas and solid targets, within the investigated energy range. The fractions were also found to be insensitive to the incident ion charge-state within the investigated energy range. The findings suggest that, for both gas and solid targets, any memory of the incident ion charge-state is lost during the early stages of the interactions and that the final charge-state distribution is determined during the final stages. A semi-classical theoretical approach based on the early Bohr theory and suggested by Bianconi et al. [18] was attempted and accounted reasonably well for the experimental results.