Is the Mössbauer effect only for gamma rays?
A common misconception is that the Mössbauer effect is limited to gamma rays, but it applies to any nuclear transition where recoil can be suppressed by a crystal lattice. In practice, it works best for low-energy gamma rays, typically below 150 keV, because higher energies cause the recoil energy to exceed the lattice binding, making recoilless emission unlikely. The most widely used isotope is iron-57, with a 14.4 keV gamma ray, but others like tin-119 and europium-151 are also common. Some critics argue the effect is too narrow in scope, but that misses the point: it is a precision tool, not a universal phenomenon. I always emphasized that the experiment must guide the theory. For instance, in my 1961 Nobel lecture, I noted that the effect's utility depends on the specific nuclear properties and lattice dynamics. One must let the experiment speak, and it has spoken clearly across many fields.
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