Mossbauer spectrometry

Mossbauer spectrometry has already been mentioned in discussing the chemical effects of nuclear reactions in solids (section 9.5). 

In order to be able to measure such small energy differences, several effects have to be taken into account. 

The natural linewidth F AE of y rays is given by the Heisenberg uncertainty principle, 

The most frequently used Mossbauer nuclide is Fe, originating from the Mossbauer source Co by electron capture (Fig. 10.1). Source and Mossbauer nuclide form a Mossbauer pair. The half-life of the first excited state of Fe at E = 14.4 keV is 98 ns (r = 1.4 x 10 s) and the natural linewidth is T = 4.6 10 eV. 

In the case of free atoms of Fe the recoil energy is = 1.95 10 - eV (eq. (9.7)), and the same kinetic energy is transferred to a free Fe atom by an incident y-ray photon of the energy E. Due to the energy E transmitted to the nuclei by recoil or absorption, the emission line is shifted to lower energies, E = E — E, and the absorption line to higher energies, E E + E, ns shown in Fig. 10.2. 

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Another relatively recent technique, in its own way as strange as Mossbauer spectrometry, is positron annihilation spectrometry. Positrons are positive electrons (antimatter), spectacularly predicted by the theoretical physicist Dirac in the 1920s and discovered in cloud chambers some years later. Some currently available radioisotopes emit positrons, so these particles arc now routine tools. High-energy positrons are injected into a crystal and very quickly become thermalised by... 

Mossbauer spectrometry is also useful to identify multiple iron species in coal and charred residues without using a concentration step. The results indicate that heat treatment of any kind, even at temperatures as low as 175°C (347°F), changes the nature of the iron species in coal. Furthermore, some kind of an association between the pyrite (FeS2) in whole coal and the organic matrix was indicated. The pyrite also appeared to be altered when the coal was heated to 175°C (347°F). 

Direct methods for determining the combinational form of an element or its oxidation state include infrared absorption spectrometry, X-ray diffraction and, more recently, electron paramagnetic resonance - nuclear magnetic resonance -and Mossbauer spectrometry. With such techniques the combinational forms of major elements in soil components such as clay minerals, iron, manganese and aluminium oxyhydroxides and humic materials and the chemical structures of these soil components have been elucidated over the past 50 years. These direct, mainly non-destructive, methods for speciation are dealt with in some detail in Chapter 3 and are not further discussed here. 

Sequential extraction of anoxic sediments often yields substantial amounts of iron in the exchangeable and carbonate extractable fraction which do not agree with patterns given by direct speciation analysis by Mossbauer spectrometry... 

Resonance gamma spectrometry or Mossbauer spectrometry can be used to study the hyperfine interactions between a nucleus and its chemical neighborhood [142], In order to examine these interactions with the help of a Mossbauer spectrometer, the first-order Doppler effect shift of the wave emitted by a moving source is applied. The arrangement used for a Mossbauer spectrometer consists of a radioactive source containing a Mossbauer isotope in an excited state (see Figure 4.54)... 

Mossbauer spectrometry is a powerful means for the elucidation of the state of iron in materials [44,138-142,145]. Figure 4.63 [44] shows the 57Fe Mossbauer spectra of the natural zeolite rocks, such as MP, C2, Cl, and C4 (see Table 4.1). In Table 4.12, the Mossbauer parameters calculated with the help of the numerical resolution of the spectra presented in Figure 4.63 are reported. That is, with the help of the recorded spectra, the accurate peak positions, integrated intensities, as well as the FWHM of each peak were calculated. This calculation was carried out by fitting the spectra with three quadrupole doublets one for site 1, another for site 2, and a last one for site 3 [44], The peaks were simulated with Gaussian functions and the fitting process for the numerical resolution of the spectra was carried was carried out with a peak separation and analysis software, developed for this purpose [44,145] based on a least square procedure [48],... 

This method is applied for the determination of the amount of magnetite present in the natural zeolite rocks C2 and C4 (see Table 4.1). The magnetite present in this zeolite was magnetically separated from the grounded samples and identified by XRD and Mossbauer spectrometry [44],... 

The gas reactants and products of the reaction were studied with a mass spectrometer and the solid reaction of the oxidation of iron was studied with Mossbauer spectrometry with electron diffraction. The Mossbauer study of the oxidized iron powder was carried out in a constant acceleration equipment [121], The electron diffraction study of the oxidized iron film, evaporated over a carbon covered transmission electron microscopy sample holder and introduced into the 5L spherical Pyrex glass container, where the Fe evaporation takes place, was carried out with the help of an Hitachi 100C transmission electron microscope [119],... 

Thus, the emitting and absorbing atoms have to be embedded in solids and both have to be kept at low temperatures, in order to measure recoilless resonance absorption of y rays. These are essential conditions for Mossbauer spectrometry. 

Applications include the use of radionuclides in geo- and cosmochemistry, dating by nuclear methods, radioanalysis, the use of radiotracers in chemical research, Mossbauer spectrometry and related methods, the use of radionuclides in the life sciences, in particular in medicine, technical and industrial applications and investigations of the behaviour of natural and man-made radionuclides, in particular actinides and fission products, in the environment (geosphere and biosphere). Dosimetry and radiation protection are considered in the last chapter of the book. 

An ideal combination is Mossbauer spectrometry, a surface analysis technique (Auger or ESCA) and the possibility of measuring back-scattering spectra. 

Nolle G, Ullrich H, Muller JB, Hesse J (1983) A microprocessor controlled spectrometer for thermal scan Mossbauer spectroscopy. Nucl Instr Meth Phys Res 207 459-463 Nomura K, UjiMra Y, Vertes A (1996) Apphcations of conversion electron Mossbauer spectrometry (GEMS). J Radioanal Nucl Chem 202 103-199... 

Chemists can legitimately ask the question whether the / values of photo-electron signals really give information about the molecule or the solid itself. Many other experimental techniques perturb the electronic structure of the groundstate much less, such as Mossbauer spectrometry, nuclear magnetic or quadrupolar resonance, or to a certain extent vibrational spectra obtained by infra-red or Raman methods. Further on, the time-scale of the other techniques tends to be much longer (22) than 10 17 sec of the photo-electron spectra. 

Caution For safety procedures see Appendix 2. Since special hardware, software, experience, and special permission are required to work with radioactive sources for high-pressure Mossbauer spectrometry, any one interested in this subject is strongly advised to contact one of the groups already working in this field before any experimental work is begun. 

R. H. Herber, Prog. Inorg. Chem., 1967,8, 1 V. 1. Goldanskii and R. Herber, Chemical Applications of Mossbauer Spectroscopy, Academic Press, 1968 N. N. Greenwood in Physical Chemistry, An Advanced Treatise, Vol. 4, Chapter 12, Academic Press, 1970 N. N. Greenwood and T. C. Gibb, Mossbauer Spectrometry, Chapman Hall, 1971. 

Blomquist J, Kjall P, Malmstrom M, Banwart S (1996) Mossbauer studies of the weathering process in some mica minerals. Conf Proc, IntT Conf Appl Mossbauer Effect 1995, SIF, Bologna, 721-724 Bonnin D, Muller S (1981) Study of the electric-field gradient in muscovite by the Mossbauer spectrometry of iron. Phys Stat Solidi C-Basic Res 105 647-657... 

The phases identified by means of XRD, eleetron diffraction and Mossbauer spectrometry are summarized in Table 1. Irradiated films appear amorphous in XRD, but the broad features observed in the diagrams are centered at the same angles than the mean peaks of a-Fe and Ni in samples containing larger crystallites. Moreover, the precipitation of Fe, Ni particles with mean diameters and standard deviations of 4 1 nm (Ni) and 4 2.5 nm (Fe) is elearly evidenced by means of TEM (Fig. 1). A broader distribution of sizes ranging from 5 to 20 nm is observed in a TH.Ni film annealed at 1000°C (the mean radius found from a set of 500 particles was smaller than the standard deviation). In addition, images of the annealed film show that the matrix is very porous. Annealed samples containing Fe have not yet been observed. 

Han] Hannoyer, B., Lenglet, M., Chopova, R., Tellier, J.C., Contribution of the Mossbauer Spectrometry and of the X-Ray Absorption Spectrometrie to the Study of Non Stoichiometry in CuFc204 (in French), Mater. Chem. Phys., 13(5), 449-465 (1985) (Crys. Structure, Eleetro-nic Structure, 18)... 

Low dose rate brachytherapy eye plaques and permanent implant sources X ray fluorescence (XRF) devices Electron capture devices Mossbauer spectrometry sources Positron emission tomography (PET) check sources 0.01 > A/D and A > exempt ... 

A11] Alleg, S., Bouzabata, B., Greneche, J.M., Study of the Local Environment during the Phase Decomposition of Fe-30.8Cr-12.2Co Alloy by Mossbauer Spectrometry , J. Alloys Compd., 312, 265-272 (2000) (Experimental, Magn. Prop., 41)... 

Cri] XRD, Mossbauer spectrometry, zero-field-cooled and field-cooled magnetization measiuements CoioCugoFcio, structure and magnetic properties of as-quenched and annealed melt-spun ribbon... 

Nas] XRD, Mossbauer spectrometry, magnetization measurements, SEM energy dispersion X-ray spectrometry CoioCu7oFc2o, structural and magnetic properties of mechanically alloyed samples, prepared in different ways... 

Lar] Magnetic and magnetoresistive measurements, XRD, Mossbauer spectrometry Co6CugoFei4, micro structure and magnetoresistive properties of the granular ball milled alloy... 

It will be interesting to explore the reactions using Lewis acids such as ZnCla, SnCU, and TiCU) by means of physical methods centered on transition metal nuclei of these Lewis acids (NMR or Mossbauer spectrometry) to discover whether true pyrylium salts are obtained directly or whether crystalline or liquid complexes of 1,5-enediones are precursors that become converted into salts only in contact with polar solvents. X-ray diffractometry of crude products may also help solve some of these problems. 

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