K-shell ionization by relativistic electron impact

K-shell ionization induced by relativistic electron impact has been studied for eleven elements of 22≤Z≤52 in the incident-electron energy region of 300–380 MeV. The I(Kβ)/I(Kα) intensity ratios and the ionization cross sections have been measured. The values of the intensity ratio are in agreement with those of previous experiments and the theoretical calculations of Scofield. Our results, along with those of previous experiments, prove the assumption that the intensity ratio is independent of the incident energy. The values of the cross section decrease with increasing Z. The decreasing tendency can be explained by Scofield’s theory, but the experimental values lie systematically lower than the calculated values. The cross sections follow a power-law dependence, σ∼$Z^{\mathrm{-}\alpha }$, and the exponent α is evaluated to be 2.51±0.13 for 300-MeV electron impact. As for the incident-energy dependence of the cross section, our results suggest a density effect in the inner-shell ionization process.