Structural Aspects of the Mössbauer Effect
In 1958 Mössbauer1 reported the results of an experiment in which he was trying to observe nuclear resonance at low temperature. Resonant absorption of γ-radiation can only be expected if the line-width of the incident radiation overlaps with that of the absorption line. According to previous work this would occur most readily at high temperature. At low temperature, therefore, loss of the resonance would be expected. In fact, Mössbauer observed the resonance to increase. The explanation of this result depends on a phenomenon which had not previously been appreciated, namely that the recoil energy loss when a gamma-ray is emitted is about 10-3 eV, enough to throw the emitting line (about 10-8 eV line-width) out of resonance. Recoil-loss induced by the outgoing gamma-ray may be reduced to about 10-8 eV by incorporating the emitter in a crystalline lattice so that emitting and absorbing lines overlap sufficiently for resonance to be obtained. This was the basis of the Mössbauer discovery. In this article illustrations are given of how the technique may be used to investigate certain aspects of structural chemistry. Attention will be primarily confined to 57Fe and 119Sn on which most of the work so far has been done.
KeywordsValence State Iron Atom Isomer Shift Electric Field Gradient Hyperfine Field
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