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

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 to 275 keV) and orientation; also detected were the scattered protons and their energy spectrum. The observations are discussed in terms of channeling 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 psi2E1 and the direction of incidence βsub(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 channeling and surface semi channeling. 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 angstroms below the surface. (author)