With the use of the generalized-oscillator-strength formulation of the plane-wave Born approximation, the contribution of individual subshell ionization and excitation to the proton stopping power is calculated for ${\mathrm{Al}}^{n+}(0\mathrm{}\le n\le 11$) for proton energies between 0.1 and 100 MeV. The neutral-A1 results are in excellent agreement with experiment. The subshell-peak stopping power due to ionization is in excellent agreement with scaled neutral-atom values. The optical oscillator strength was used to calculate the Bethe meanexcitation energy $I$ for all the A1 ions. Equating the explicitly calculated stopping power at 100 MeV to the Bethe formula led to an alternative $I$ value. While the two $I$ values agreed for some ions, for others they disagreed by as much as 50%. However, even in such cases, a change of less than 10% in the stopping power at 100 MeV would produce agreement between the two methods of calculating $I$.

• Received 20 November 1981

DOI:https://doi.org/10.1103/PhysRevA.26.1318