Channeling and blocking phenomena. Definitions - Generalities

The main aspects of channeling and blocking are: incident charged projectiles are steered through a crystal lattice if their angle of incidence is close to a major axial or planar lattice direction (channeling of collimated beams). Channeled particles exhibit an unique impact parameter distribution with high flux density between rows and planes, and almost zero flux density at the regular sites of the target atoms. Due to this impact parameter distribution nuclear and electronic energy loss is reduced. Reactions with target atoms which require close collisions are drastically suppressed, whereas the interactions of the projectiles with interstitial or displaced atoms is enhanced. The propagation of projectiles starting from a lattice site in a solid is suppressed along lattice planes and atomic rows because of the shadow produced by scattering at the neighbouring atoms in these planes and rows (blocking of randomly incident projectiles along major axial and planar directions