MossbauerNobelAddress

Recoilless nuclear resonance absorption of gamma radiation

All attempts in the next two decades to find this nuclear resonance absorption provedfruitless. Before I can approach the subject of my talk, it is appropriate to consider the reasons why the discovery of nuclear resonance absorption was solong delayed.
Such extraordinarily sharplines exhibitingthe naturalline width are normally not observed. Rather, a series of side effects al ways exist, whichlead to considerable broadening such that the line widths ordinarily associated with low-energy gamma transitions exceed the natural minimu m width by many orders of magnitude. The most important broadening mechanism is thethermal motion of the nuclei in the source and in the absorber;this leads to Doppler shifts in the energy of the gamma quanta and therefore produces correspondingline broadenings.

Even at emperature drop to absolute zero does not extinguish this thermal broadening, since the existence of zero-point energy at absolute zero frequently produces, at least in solids, line widths of the sa me order of magnitude as the ones existing at roo m temperature.