The ion fractions η + of low energy (5–10 keV) argon particles scattered from a Cu(100) surface, are measured with a time of flight spectrometer. Neutral as well as charged projectiles are used. The scattering angle θ is 30°. The results for different angles of incidence ψ and crystal directions are reported. For scattering in the 〈100〉 direction, with a ψ-value of 15° and a primary energy E 0 of 5 and 10 keV, the ion fractions for the quasi single scattering peak, η + QS, are 1.5 and 6.1% respectively. When E 0 is between 5 and 10 keV a reionization process with a constant reionization probability occurs during the violent interaction. This process, but also neutralization along the outgoing trajectory, determines η + QS. With ions as projectiles, an energy difference of about 16 eV is observed between the quasi single scattering peaks in the spectra of all scattered particles and of ions only. The ion fraction for the quasi double scattering peak, η + QD. depends largely upon E 0, indicating that the efficiency of the reionization process increases with E 0. A qualitative discussion of the data is given, using the reionization process and the interatomic neutralization processes along the trajectory of the scattered particles.