Scattering, energy loss and X-ray production of protons of 150–275 keV at grazing incidence on tungsten crystals

Abstract

Experiments are reported in which a finely collimated beam of protons were incident on a flat tungsten crystal or an amorphous WO₃ surface, The yields of W (M shell) or O (K shell) X-rays were measured as a function of proton energy (150–275 keV) and orientation; also detected were the scattered protons and their energy spectrum. The observations are discussed in terms of channelling theory and projected motion in the plane transverse to the atomic rows. By a combination of analytical theory and computer simulation it is shown that in this plane the kinetic energy ψ² E ₁ and the direction of incidence β _in should be the determining factors of yield and scattering. The observations bear this out and special two-dimensional processes can be identified such as trajectory focusing, quasi-planar channelling and surface semi channelling. Oxygen in the crystal surface is detected and shown to lie on a different lattice from the tungsten, to have a surface stoichiometry close to WO₃ and to extend some 10 A below the surface.