Mossbauer effect When an atom bound in a crystal a lattice emits a gamma ray, the crystal as a whole takes up the recoil momentum. The recoil momentum is negligible since the crystal contains a large number of atoms. The gamma ray photon takes the full excitation energy of the nucleus and the gamma ray frequency is extraordinarily sharp.

The effect has been successfully used as high precision frequency standard for testing several predictions of special and general theory of relativity.