Mössbauer spectroscopy (rus. спектроскопия, мёссбауэровская otherwise метод ядерного гамма-резонанса; гамма-резонансная спектроскопия) — a family of methods based on the Mössbauer effect designed to study physical and chemical properties of condensed matter (mostly solids) as well as micro- and nano-sized objects (nuclei, ions, chemical and biological systems, etc.) in solid bodies.

Description

The Mössbauer spectroscopy method is based on the effect of recoil-free resonant absorption of monochromatic quanta in the state with energy equal to the Mössbauer transition energy.

To apply this method, radioactive isotopes are used: for instance, isotope 57Fe transforms into 57Co converted with emission of which results in there being no resonant absorption.

To achieve the resonance, the source of -quanta is moved with a certain velocity () relative to the absorber and, therefore, the source's nuclear transition energy  changes (the Doppler effect* occurs); when is reached -quant is absorbed by the nucleus and nuclear gamma resonance originates. The energy differences observed in Mössbauer spectroscopy correspond to relative velocities of the order of a millimetre per second which are easily achieved and reliably registered.

When measured, the Mössbauer spectrum represents the dependence of intensity of -rays absorption from . The quantitative measure of intensity of -radiation is the number of electrical pulses generated in a strictly defined period of time.

There are two types of Mössbauer spectroscopy: absorption and emission spectroscopy. In the first case the studied material is an absorber of -quanta, and to obtain the Mössbauer spectrum we need the content of the Mössbauer atoms in the sample to amount to several percent of the total number of atoms. For example, the content in native iron of 57Fe isotope is sufficient for this method since this number is 2.17%.

The difference between Mössbauer emission spectroscopy and Mössbauer absorption spectroscopy is that the research subjects are substances containing radioactive nuclei which form, through nuclear reactions and subsequent cascade of -transitions, an excited nucleus emitting resonant -quanta. The energy spectrum of emitted -quanta is analysed with the use of the Mössbauer spectrometer where the absorber contains resonant nuclei which remain in the ground state and have a single absorption line.

Mössbauer spectroscopy is one of the main methods used to study the structure of iron-containing nanoparticles. Iron doping facilitates the study of many other nanostructured materials and some nanoscale processes (e.g., release of impurities on the surface of nanoparticles, the kinetics of nanoparticles formation, etc.).


* The Doppler effect is the change in perceived vibrations frequency due to movements of wave source and/or receiver.

Illustrations

Simplified layout of Mössbauer spectrometer; a mechanical or electrodynamic device drives the q
Simplified layout of Mössbauer spectrometer; a mechanical or electrodynamic device drives the quantum source, making it oscillate with a certain speed  relative to the absorber. The detector measures the relation of intensity of -quanta stream passing through the absorber to the speed of oscillation.

Author

  • Streletskiy Alexey V.

Sources

  1. G. K. Wertheim, Mössbauer Effect: Principles and Applications // Academic Press, 1964.
  2. Mössbauer spectroscopy // Physical Encyclopedic Dictionary (in Russian) // Moscow: The Great Soviet Encyclopedia, 1995. — 928 с.

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