Partial Mossbauer effect—Why not?

[jimgraber]

A photon can be absorbed by a crystal. The recoil is absorbed by either a single atom (ordinary absorption) or by the entire crystal (Mossbauer effect) Why do we not observe absorption by two or three atoms at the small end or by one half or one third of the crystal at the high end?
TIA.
Jim Graber

 

[genneth]

Gamma radiation involves kicking out a photon, so by conservation of momentum some momentum has to be imparted to the thing that emitted it. However, in a crystal, momentum can be absorbed into lattice vibrations as phonons. The latter are quantised in energy and momentum, so there is a possibility of no phonons being excited. If you were to manage to excite one or two phonons I guess that would correspond to your case of partial Mossbauer effect? The only problem is that phonons carry *much* more momentum than photons, so even one or two may cause sufficient broadening for the effect to be described as effectively having disappeared.

 

[denian]

The Mossbauer effect is a phenomenon that occurs when a photon is absorbed by a crystal and the recoil energy is absorbed by the entire crystal, resulting in a sharp spectral line. This effect is typically observed when the crystal is in a highly ordered state, such as at low temperatures.

The reason why we do not observe absorption by two or three atoms at the small end or by one half or one third of the crystal at the high end is because the Mossbauer effect requires a high level of crystal order and symmetry. If the crystal is not perfectly aligned, the recoil energy will not be evenly distributed among all of the atoms, leading to a broadening of the spectral line. Additionally, the energy levels of the atoms within the crystal must be closely matched for the Mossbauer effect to occur.

Furthermore, at the small end of the crystal, the atoms are too close together for the recoil energy to be absorbed by just a few atoms. It would require a significant amount of energy to move just a couple of atoms, and this energy would be quickly dissipated throughout the crystal. Similarly, at the high end of the crystal, the atoms are too far apart for the recoil energy to be absorbed by just a fraction of the crystal.

In summary, the Mossbauer effect is a highly specific phenomenon that requires a perfect alignment of atoms and energy levels within the crystal. Any deviations from this ideal state will result in a broadening of the spectral line and a loss of the sharp Mossbauer effect.