Atomic recoil is the result of the interaction of an atom with an energetic elementary particle, when the momentum of the interacting particle is transferred to the atom as whole without altering non-translational degrees of freedom of the atom. It is a purely quantum phenomenon. Atomic recoil was discovered by Harriet Brooks, Canada's first female nuclear physicist.
If the transferred momentum of atomic recoil is enough to disrupt the crystal lattice of the material, a vacancy defect is formed otherwise a phonon is generated.
Closely related to the atomic recoil is the electron recoil, (see photoexcitation and photoionization).
Another form is the nuclear recoil, when momentum transfers to the atomic nucleus as whole.
In some cases quantum effects can forbid momentum transfer to an individual nucleus, and momentum is transferred to the crystal lattice as a whole. (see Mössbauer effect)