Mossbauer elements

Mossbauer spectroscopy is based on the phenomenon of recoil-free resonant absorption of y rays by atomic nuclei, and the spectrum reflects the perturbation induced in the nuclear levels due to the interaction of the Mossbauer atom with its chemical environment. The Mossbauer elements, iron and tin, can be used conveniently as in situ probes in environmental and geochemical applications. Since Mossbauer spectroscopy has now become relatively familiar to chemists, I present here only a brief description of typical experimental techniques used in Mossbauer measurements. There are two types of Mossbauer measurements transmission method and scattering method. 

Gold ( Au) is another Mossbauer element that can possibly be employed in archaeological applications. However, Au studies vdll be fairly limited in practice, since samples must be cooled dovm to very low temperatures. 

Iron, tin, antimony, tellurium, iodine, xenon, europium, gold and neptunium are useful Mossbauer elements while nickel, ruthenium, tungsten and iridium can also be used but with greater difficulty. Much of the work reported in the lit-... 

Mossbauer elements for lithium-ion batteries. White box Elements with known Mossbauer isotopes. Gray box Elements with Mossbauer isotopes and tested in lithium batteries. Black box Elements with Mossbauer isotopes and used in commercial Li-ion batteries. 

Mossbauer spectroscopy is a specialist characterization tool in catalysis. Nevertheless, it has yielded essential information on a number of important catalysts, such as the iron catalyst for ammonia and Fischer-Tropsch synthesis, as well as the CoMoS hydrotreating catalyst. Mossbauer spectroscopy provides the oxidation state, the internal magnetic field, and the lattice symmetry of a limited number of elements such as iron, cobalt, tin, iridium, ruthenium, antimony, platinum and gold, and can be applied in situ. 

In Mossbauer emission spectroscopy one prepares the catalyst with the radioactive source element (e.g. Co) and uses a suitable moving single-line absorber of Fe to record the spectra. In this way one can also study Co-containing catalysts, although strictly speaking the information concerns the iron in the catalyst that forms by the Co —> Fe decay process. 

The great advantage of Mossbauer spectroscopy is that it can be applied in situ. The major limitation of the technique is that it can only be applied to a couple of elements, among which iron and tin are the easiest to study. 

Up to the present time, the Mossbauer effect has been observed with nearly 100 nuclear transitions in about 80 nuclides distributed over 43 elements (cf. Fig. 1.1). Of course, as with many other spectroscopic methods, not all of these transitions are suitable for actual studies, for reasons which we shall discuss later. Nearly 20 elements have proved to be suitable for practical applications. It is the purpose of the present book to deal only with Mossbauer active transition elements (Fe, Ni, Zn, Tc, Ru, Hf, Ta, W, (Re), Os, Ir, Pt, Au, Hg). A great deal of space will be devoted to the spectroscopy of Fe, which is by far the most extensively used Mossbauer nuclide of all. We will not discuss the many thousands of reports on Fe... 

Fig. 1.1 Periodic table of the elements those in which the Mossbauer effect has been observed are marked appropriately. (Taken from the 1974 issue of [10])...

Mossbauer spectra of layered samples are influenced by various parameters, such as the thickness of the layers, the density of the sample, and its elemental... 

In addition to the Mossbauer data, SDDs allow the simultaneous acquisition of the XRF spectrum, thus providing data on the sample s elemental composition. A new control- and readout-electronics for MIMOS llA allows spectra acquisition at highest possible count rates available at a total detector area of 360 mm. ... 

Fig. 3.25 Left signal-to-noise ratio (SNR) of the Mbssbauer spectra of a basalt taken with MIMOS II (full SI-PIN detector system black data-points) and MIMOS IIA (1/4 of full SDD system red data-points) respectively. Right XRF spectra of low Z elements measured with MIMOS IIA (SDDs) at —20°C. The Compton scattered 14.4 keV line (at 13.8 keV) and the resonant 14.4 keV Mossbauer line are well separated...

The parameters that Mossbauer spectroscopy is sensitive to depend on the immediate vicinity of the absorbing nucleus. However, for heavier elements, the electrons close to the nucleus move at high velocities, close to the speed of light. In this situation, relativistic effects become significant and should be treated at some level of detail. 

The previous chapters are exclusively devoted to the measurements and interpretation of Fe spectra of various iron-containing systems. Iron is, by far, the most extensively explored element in the field of chemistry compared with all other Mdssbauer-active elements because the Mossbauer effect of Fe is very easy to observe and the spectra are, in general, well resolved and they reflect important information about bonding and structural properties. Besides iron, there are a good number of other transition metals suitable for Mossbauer spectroscopy which is, however, less extensively studied because of technical and/or spectral resolution problems. In recent years, many of these difficulties have been overcome, and we shall see in the following sections a good deal of successful Mossbauer spectroscopy that has been performed on compounds of... 

RBa2Cu307 (R = rare earth element or Y), La2 (5r,.Cu04 (0 < X < 0.3) Eu-155(Gd-155) emission Mossbauer spectroscopy, EFG tensor at R sites, in good agreement with point charge model when holes are supposed to be mainly in sublattices of the chain and at oxygen in Cu-O plane... 

The miniaturized Mossbauer instruments have proven as part of the NASA Mars Exploration Rover 2003 mission that Mossbauer spectroscopy is a powerful tool for planetary exploration, including our planet Earth. For the advanced model of MIMOS II, the new detector technologies and electronic components increase sensitivity and performance significantly. In combination with the high-energy resolution of the SDD, it will be possible to perform XRF analysis in parallel to Mossbauer spectroscopy. In addition to the Fe-mineralogy, information on the sample s elemental composition will be obtained. 

The Mossbauer effect as a spectroscopic method probes transitions within an atom s nucleus and therefore requires a nucleus with low-lying excited states. The effect has been observed for 43 elements. For applications in bioinorganic chemistry, the 57Fe nucleus has the greatest relevance and the focus will be exclusively on this nucleus here. Mossbauer spectroscopy requires (a) the emission of y rays from... 

The recoilless nuclear resonance absorption of y-radiation (Mossbauer effect) has been verified for more than 40 elements, but only some 15 of them are suitable for practical applications [33, 34]. The limiting factors are the lifetime and the energy of the nuclear excited state involved in the Mossbauer transition. The lifetime determines the spectral line width, which should not exceed the hyperfine interaction energies to be observed. The transition energy of the y-quanta determines the recoil energy and thus the resonance effect [34]. 57Fe is by far the most suited and thus the most widely studied Mossbauer-active nuclide, and 57Fe Mossbauer spectroscopy has become a standard technique for the characterisation of SCO compounds of iron. 

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