Mössbauer spectroscopy
Description
The Mössbauer effect is the recoilless nuclear resonance absorption and emission of gamma-rays, similar to the acoustic resonance between two tuning forks with the same frequency for sender and receiver. A nucleus with Z protons and N neutrons in an excited state of energy Ee and mean lifetime τ of typically 100 ns undergoes transition to the ground state of energy Eg by emitting a gamma photon of energy Eg = Ee – Eg . The gamma photon may be absorbed by a nucleus of the same kind (same Z and N) in its ground state, whereby transition to the excited state of energy Ee, takes place (resonance absorption). The subsequent transition to the ground state emits again a gamma photon (resonance fluorescence) or a conversion electron e– (with nearly ten times higher probability than gamma emission). The mean lifetime τ determines the width of the resonance lines. Resonance absorption is observable only if the emission and absorption lines overlap sufficiently. By emission or absorption of gamma photon with energy Eg in a freely moving atom or molecule (gas, liquid), the atom (molecule) of mass m suffers a recoil effect which is several orders of magnitude larger than the natural line width. No resonance is possible between free atoms or molecules This phenomenon was discovered by the German physicist Rudolf L. Mössbauer which became known as the Mössbauer Effect. He was awarded the Nobel Prize for Physics in 1961. Môssbauer spectrometers, generally equipped with a cobalt 57 radioactive sealed source are used to characterise oxidation state of iron compounds, like pigments (differentiation between hematite, alpha-Fe2O3 , and goethite, alpha-Fe00H), corrosion products…
spectrométrie Mössbauer (Fr.), Mössbauer Spektroskopie (Deut.)
Additional information
- P. Gütlich, C. Schröder & V. Schünemann, Mössbauer spectroscopy - an indispensable tool in solid state research, Spectroscopy Europe, 24, 4, 21-32 (2012)
- P. Gütlich, E. Bill & A. X. Trautwein, Mössbauer spectroscopy and transition metal chemistry – Fundamentals and applications, Springer Verlag, Heidelberg (2011)
- G. Klingelhöfer, G. M. da Costa, A. Prous & B. Bernhardt, Rock paintings from Minas Gerais, Brazil, investigated by in-situ Mössbauer spectroscopy, Hyperfine Interactions, C5, 423 , Springer Verlag (2002)