Mössbauer effect (rus. эффект Мёссбауэра) — An effect of gamma-quanta resonance absorption by atomic nuclei without recoil energy losses.

Description

Atomic nuclei can be in the ground and excited states. The transition of the nucleus from one state to another occurs either in the absorption or emission of a shortwave gamma ray (Fig. a). Gamma ray energy is determined by the difference in energy between the ground and excited states of the atomic nucleus (ET), the nuclear recoil energy (R ~ 10-1 eV for free atoms) and the Doppler shift (D), caused by the nuclear translational motion:

Eemission = ET - R ± D (gamma quantum energy emitted by the source),

Eabsorption = ET + R ± D (gamma quantum energy adsorbed by the sample).

The resonance condition occurs when the nucleus in the ground state absorbs the gamma-ray emitted by the excited nucleus:

Eemission ≈ Eabsorption.

Graphically, this condition can be shown by overlapping areas of the distribution curves by energy of quanta emitted and absorbed (Fig. b). The probability of the resonance process increases when the emitting nucleus and the absorbing nucleus are fixed in a rigid crystal lattice. In this case, when the photon is absorbed, the recoil energy transforms into the vibration energy of the crystal lattice, i.e. a whole solid gets the recoil. Since the body weight is infinitely larger than that of a single atom, the recoil energy becomes negligibly small (R ~ 10-4 eV).

The resonance effect is normally observed only in solids in the case of the nuclei of stable isotopes (they are about 80), the most widely used ones being Fe57 and Sn119. By measuring the probability of the Mössbauer effect and its dependence on temperature we can get information on the atomic interactions in solids and about the lattice vibrations. This is what makes the Mössbauer effect widely used as a method of analysing solids (see Mössbauer spectroscopy).

Illustrations

a-the scheme of gamma-quantum resonant absorption; b —emitted and absorbed gamma quanta energie
a-the scheme of gamma-quantum resonant absorption; b —emitted and absorbed gamma quanta energies distribution.

Author

  • Streletskiy Alexey V.

Sources

  1. Russell S. Drago, Physical Methods for Chemists 2nd ed, Saunders College Publishing, 1992.
  2. Vilkov, L.V., Pentin, Yu.A. Physical methods of investigation in chemistry. Structural Methods and Optical Spectroscopy (in Russian). Moscow: Vysshaya Shkola 1989. - 288pp.

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