Mossbauer vibrating source

As discussed in Sects. 3.1.1-3.1.3, successful acquisition of Mossbauer spectra depends on accurate knowledge of the relative velocity of the source and sample. External vibrations that impart differential velocity components to the source and sample would degrade the quality of the Mossbauer spectrum. This degradation... 

Quasielastic (Rayleigh) scattering of the 46.5 keV Mossbauer radiation was used to examine the liquid dynamics of glycerol [245, 246] and the harmonic vibrations of the nonhydrogen atoms in polycrystalline myoglobin [247] as a function of temperature. The y-quanta emitted by the Mossbauer source are... 

The conclusion of all this is the following. If we place our two atoms in a lattice and do the experiment under conditions where recoil energy of the photon emission and absorption are significantly smaller than the energy of the lattice vibrations, a fraction of the photons emitted by the source nucleus will be absorbed by the nucleus in the absorber. This is the Mossbauer effect, named after Rudolf L. Mossbauer, who discovered it in 1957 and received the Nobel Prize in 1961 [9]. 

Synchrotron-based nuclear resonance methods have revealed the vibrational dynamics of the iron atom in numerous systems, including alloys, amorphous materials, nanomaterials, and materials under high pressure. The above-mentioned selectivity for the probe nucleus is particularly valuable for biological macromolecules, which may contain many thousands of atoms, but a localized active site is often the true center of interest. Since its availability, NRVS has been applied to study the vibrational dynamics of Fe in proteins, porphyrin model compounds, " and iron-sulfur clusters. It is shown that NRVS can provide frequencies, amplitudes, and directions for Fe vibrations in the samples. It helps to clarify mode assignments in vibrational spectra and reveals many important vibrational modes of Fe that cannot be seen by other methods. In particular, NRVS reveals low-frequency motions of the Fe down to below 100 cm that control biological reactions. The applications presented here use Fe as the probe nucleus, but the principle applies to other Mossbauer isotopes such as " Sn, Kr, Ni, and Zn if appropriate sources are available. 

Schematic transmission Mossbauer spectrum bottom) with notations for the simpiest arrangement (top). Either the source or the absorber is vibrated by a transducer. As usuai, positive Doppier veiocities (u) refer to approaching source and absorber...

Since the Mossbauer effect is intimately related to any motion of the emitting or absorbing nucleus on either a microscopic or macroscopic scale, Mossbauer spectroscopy provides a potential means by which information on nuclear dynamics, and hence on the dynamics of a system in which the Mossbauer nucleus acts as a probe, can be obtained. Any motion of the Mossbauer nucleus can influence the Mossbauer spectrum in two ways. Firstly, because this motion may be related to the vibrational properties of the system it can influence the recoil-free fraction and hence the absorption intensity of the spectrum itself. Since the absolute absorption intensity is dependent on a large number of other factors, which may be diflicult to determine accurately, any change in recoil-free fraction is most usefully followed as a function of temperature in order to obtain information on the vibrational properties of the system. The second way in which the effects of any motion of the Mossbauer nucleus in the source or absorber are manifested is in the Mossbauer spectroscopic linewidths, as this motion can be thought of as an additional Doppler motion which may partially smear out the resonant absorption. Since the linewidths are also... 

For the absorption process, the same conservation law should be satisfied. For the transition Eq — 14.4 keV in Fe, / is 1.9 X 10 eV which is 10 times large compared to the natural line width of the excited state and no resonance between source and absorber for the free nucleus can be expected. When the nucleus is bounded into the solid, the recoil energy can be dispersed by the excitation of the solid. When the source and absorber are the nuclei embedded into the solid, recoil energy R may be used for the excitation of phonon that is the vibration state of sohd. Phonon is quantized as discrete value in solid and in usual metals the excitation energy of phonon states is the order of 10 -10 eV and there is rather large probability to have a zero phonon excitation in emission and absorption process in other word, the recoilless emission and recoilless resonant absorption of photon. This is the most important characteristic feature of the Mossbauer effect. As a consequence, the y photon emitted by the decay from the first excited state that has a... 

Fig. 2.44 The sensor head of the miniaturized Mossbauer spectrometer MIMOS contains the drive (vibrating) unit, the Mossbauer source, the detectors and amplification electronics. MIMOS is set up in backscattering geometry [77, 78]...

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