Angular distribution of fast charged particles reflected by the surface of a single crystal

Backscattered particles with energy (E/sub f/) close to the incident energy (E/sub i/) escape the monocrystal target from the thickness which is smaller or comparable with the inelastic scattering length. In the case of small energy losses E/sub i/-- E/subf//E/sub i/ much less than 1, the angular distribution of the backscattered particles corresponds to the usual Rutherford scattering if the incident and final directions of the particle momenta do not coincide with crystallographic axes. When the incident momentum direction and/or the backscattered momentum direction coincides with any crystallographic axis, the blocking effect essentially reduces the scattering of the fast charged particles. When the energy losses are not small enough, the differential backscattering coefficients of fast charged particles for a single crystal and for an amorphous medium coincide, provided that the incident and final directions are not parallel to crystallographic axes. In the opposite case the channeling effect for positive charged particles leads to the essential decrease of the differential backscattering coefficient. (U.S.)