Relative $K$-shell ionization cross sections were measured for 7.1-MeV/amu projectiles of ${\mathrm{He}}^{2+}$, ${\mathrm{B}}^{5+}$, ${\mathrm{C}}^{6+}$, ${\mathrm{N}}^{7+}$, ${\mathrm{O}}^{8+}$, ${\mathrm{F}}^{9+}$, and ${\mathrm{Ne}}^{10+}$ on targets of Ca, Fe, Y, and Cd. The scaled cross section ratios $R=\frac{\left[4\mathrm{}\sigma \right(Z_1\left)\right]}{\left[Z_1^{}{}_{}{}^2\sigma \mathrm{}\right(2\left)\right]}$ exhibit linear $Z_1$ dependence characteristic of the effects of increased binding of target electrons and polarization. The absence of higher-order $Z_1$ dependence suggests that the contributions to the ionization $\sigma$ by charge exchange to the empty orbitals of the projectile are relatively small.

• Received 18 March 1974

DOI:https://doi.org/10.1103/PhysRevLett.32.1155