OxygenK-shall X-Ray production in thin films of aluminum oxide by 20- to 100-keV protons

The oxygen $K$-shell x-ray production cross section and the stopping power of aluminum oxide for 20- to 100-keV protons were determined by measurements of the oxygen $K$ x-ray yield (x rays/proton) from surface films of aluminum oxide, formed on aluminum substrates by anodic oxidation. Ionization cross-section results are compared with previous measurements of C, Mg, and Al. The comparison shows that the cross sections follow the same trend, but depart from theoretical predictions based on the Born approximation. The stopping power data have maxima at proton energies of 65 and 90 keV, corresponding to peaks in the stopping powers of Al and O.