Measurement of theK-Shell Ionization Cross Sections of Al and Mg for 1- to 5-MeVαParticles

The $K$-shell ionization cross sections of Al and Mg for 1- to 5-MeV $\alpha$ particles have been obtained from measurements of the fluorescent x-ray yields of thin foils irradiated by $\alpha$ particles. The results for Al range from (0.36 ± 0.31) × ${10}^{-20\mathrm{}}$ ${\mathrm{cm}}^2$ at 1.0 MeV to (13.47 ± 0.77) × ${10}^{-20\mathrm{}}$ ${\mathrm{cm}}^2$ at 5.0 MeV, and for Mg from (1.04 ± 0.25) × ${10}^{-20\mathrm{}}$ ${\mathrm{cm}}^2$ at 1.0 MeV to (16.61 ± 0.56) × ${10}^{-20\mathrm{}}$ ${\mathrm{cm}}^2$ at 5.0 MeV. The energy dependence is stronger than predicted by the Born approximation. The data are compared with theoretical calculations and with other experimental results for protons, ${\mathrm{He}}^3$, and $\alpha$ particles.