The system exposed to irradiation with 11 - 12 MeV electrons was studied by soft-x-ray emission spectroscopy using the variable-exciting-electron-energy, optical ellipsometry, and nuclear reaction techniques. For the system prepared on an n-substrate, oxidation of Si was observed, and the thickness of the layer after electron irradiation was estimated. For the system prepared on a p-Si substrate, irradiation-induced oxidation was not observed. It was found that preliminary boron implantation in the -Si system blocks oxidation of the n-Si substrate exposed to electron irradiation.