How does the Mössbauer effect work?
The Mössbauer effect relies on embedding radioactive nuclei in a solid crystal lattice. Normally, when a nucleus emits a gamma ray, it recoils, shifting the gamma ray's energy slightly and preventing resonance absorption by another nucleus. But in a crystal, the lattice as a whole absorbs the recoil momentum, making it negligible. This means the emitted gamma ray retains its full energy, allowing it to be resonantly absorbed by a target nucleus of the same isotope. I demonstrated this using iridium-191 in my 1958 paper 'Kernresonanzfluoreszenz von Gammastrahlung in Ir191.' The key is that the crystal must be cooled to reduce thermal vibrations, which otherwise blur the resonance. By moving the source relative to the absorber at tiny velocities—millimeters per second—I could Doppler-shift the gamma ray energy and map the absorption spectrum with extraordinary precision. Nature does not reveal her secrets easily; one must let the experiment speak.
Ask Rudolf Ludwig Mössbauer the follow-up →