When a particle crosses a material which does not present strong symmetries (e.g.  amorphous) it experiences a large number of uncorrelated interactions with the atoms compounding the material. Depending on the impact parameter and energy  of the particle, a large variety of interactions, both elastic and inelastic, are possible: multiple Coulomb scattering, Rutherford scattering, ionization, elastic, quasi elastic and inelastic point-like interactions. A complete description of these effects, which are dominating in standard collimation materials, can be found in [1].

Even if these interactions occur also in a misaligned crystal, here we will focus on the effects which take place when the impinging particle is well oriented along the main symmetry axes/planes of the crystal lattice structure. These interactions are called coherent interactions, because the particles interact with a subset of atoms arranged in a specific geometrical layout (e.g. a plane or an axis of the lattice) instead of interacting separately with each individual atom. The kind of coherent effect which takes place depends on the relative orientation between the particle velocity and the crystal lattice.

- In case of orientation with respect to a plane, we have planar channeling both for straight and bent crystals or volume reflection (for bent crystals). Secondary effects are dechanneling and volume capture.

- In case of orientation with respect to a crystal axis, we will have axial channeling.

Bibliography

Inelastic nuclear interactions at protons multiple passage in bent crystals
A Babaev and S. B. Dabagov

Simulations of planar channeling of relativistic nuclei in a bent crystal
A. Babaev and S.B. Dabagov