K-Shell Ionization Cross Sections of Selected Elements from Fe to As for Proton Bombardment from 0.5 to 2.0 MeV

The $K$ -shell ionization cross sections for Fe, Co, Cu, Zn, Ga, Ge, and As were measured for proton impact in the range 0.5 to 2.0 MeV. The cross sections were found to be 242±23, 173±15, 94.1±7.8, 70.9±6.9, 56.4±4.6, 36.5±2.7, and 27.1±2.1 b, respectively, at 2.0 MeV. These measurements agree to within less than 17% with predictions of the binary-encounter approximation. Predictions of the plane-wave Born approximation exceed the measured values by approximately a factor of 2 at the maximum deviation. Corrections suggested by Brandt et al. account for this descrepancy. These measurements also indicate a trend for the measured ionization cross sections to drop below the theoretical predictions for low projectile energies.