Mossbauer spectroscopy recoil-free fraction

The example is typical for many applications of Mossbauer spectroscopy in catalysis a catalyst undergoes a certain treatment, then its Mossbauer spectrum is measured in situ at room temperature. Flowever, if the catalyst contains highly dispersed particles, the measurement of spectra at cryogenic temperatures becomes advantageous as the recoil-free fraction of surface atoms increases substantially at temperatures below 300 K. Secondly, spectra of small particles that behave superparamagne-... 

Wender and Hershkowitz [237] used the sensitivity of the recoil-free fraction in tungsten Mossbauer spectroscopy to deduce the effect of irradiation of tungsten compounds by Coulomb excitation of the resonance levels (2 states of I82,i84,i8 y with 6 MeV a-particles. While no effect of irradiation on the/-factors could be observed for tungsten metal in agreement with [233], a decrease of/was measured for WC, W2B, W2B5, and WO3 after irradiation. 

Let us now discuss some recent work by Sano and myself on completely characterizing barium stannate, a material first proposed by Plotnikova, Mitrofanov, and Shpinel (21), as a source for tin Mossbauer spectroscopy. It is easily prepared, is a stoichiometric compound and has all the properties one desires in a Mossbauer matrix. The recoil-free fraction at room temperature is about 0.55 with about a 10% error. The line width extrapolated to zero absorber thickness is about 6% larger than natural—i.e., the line width observed is ca. 0.318 mm./sec. at zero ab-... 

Mossbauer spectroscopy may be used for semi-quantitative or qualitative determination of Fe2 /Fe3 ratios Table II shows that a rather good correlation exists between Mossbauer and chemical analysis for Fe2 /Fe3 ratios in clay mineral samples, but these measurements must be obtained at lower temperatures (< 150 K) in order to maximize the recoil-free fractions of both valence states in the sample ... 

Mossbauer spectroscopy is the study of recoilless resonant fluorescence " Sn Mossbauer spectroscopy has been found to be a most usefifl method for studying the bonding and stereochemistry of tin compounds in the solid state. The two most important parameters are the isomer shift (5, mm s ) and the quadrupole sphtting (A q, nuns ), although the recoil-free fractions and temperature coefficients can also supply useful structural indications. 

Mossbauer spectroscopy has proved to be of great value in inorganic tin chemistry (Table 6). Particularly useful have been isomer shift (5) and quadrupole splitting (A) data. The recoil-free fraction and its temperature coefficient are other parameters that have found use in structural elucidations variable temperature Mossbauer studies can be used, for example, in gaining information regarding the degree of aggregation in solid tin compounds. 

Ichikawa et al (36,45) from the temperature dependence of the recoil-free" fraction in Mossbauer spectroscopy were able to extract evidence about the uniform distribution of FePc complexes in zeolite Y. 

Mossbauer spectroscopy is a powerful technique that may give information on the occurrence of tin and organotin polymeric structures. This is made possible through the investigation of molecular dynamics of " Sn nuclei embedded in molecular fragments and in particular through the well established correlation between the recoil free fraction of yrays (Debye-Waller-Mossbauer or Lamb-Mossbauer factor) and the mean square displacement of the nuclei (or of the masses bound to the Mossbauer nuclei). This correlation appears to be a linear dependence of the logarithm of the resonant peaks area, InA (proportional to Lamb Mossbauer factor,/ ) and the absolute temperature, T. 

The recoil-free fraction in Mossbauer spectroscopy is equivalent to the fraction of X-ray scattering processes without lattice excitation this fraction of elastic processes in X-ray and neutron diffraction is described by the Debye-Waller factor ... 

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... 

M.D. Dyar, R.L. Klima, D. Lindsley, C.M. Pieters, Effects of differential recoil-free fraction on ordering and site occupancies in Mossbauer spectroscopy of orthopyroxenes. Am. Mineral. 92, 424-428 (2007)... 

A large number of review papers [1-4] and monographs [5-9] have already been published on the theory and application of recoil-free nuclear resonance absorption. The greater fraction of Mossbauer spectroscopy research has been carried out in the field of inorganic chemistry [7, 10-13] and vitreous materials [14-18] using Fe and Sn. It is also possible to apply the Mossbauer effect to biological research [11, 13] too. 

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