The Mössbauer effect occurs when atoms are in a solid lattice or matrix. The chemical binding energies in solids (1-10 ) are much greater than free atom recoil energies, . The mass, , recoiling then becomes effectively that of the entire crystal, which can be of the order of greater than a single atom. It can be seen from equations 2.1 and 2.2 that and will now be negligible in this case.
However, although the nucleus is bound within the lattice it is still free to vibrate. The recoil energy can still be transferred to the lattice as a quantised lattice vibration, or phonon. If the recoil energy is less than the lowest quantised vibrational mode then a recoil-free event will occur. The probability of such an event is governed by the recoil-free factor, , which is given as
Dr John Bland, 15/03/2003