Rudolf Mössbauer discovered in 1957 that transitions from an excited nuclear state occur with negligible nuclear recoil when the nucleus is embedded in a large crystal lattice because the entire lattice absorbs the recoil. A transition like that in 191Ir from the 129- keV excited state to the ground state has a lifetime of 1.9 X 10-10 s.
(a) Determine the energy width of the decay.
(b) Similarly, if the photon is absorbed by 191Ir embedded in a crystal, the recoil is negligible. How- ever, even a slight motion of the absorber will lead to a Doppler shift suf?cient to destroy the resonance absorption. Calculate the speed necessary to shift the energy absorption by 5f, where f is the nuclear decay width. This effect is called the Mössbauer effect.