Emission Mossbauer spectroscopy

Figure 4.16. To cover all possible transitions in the absorbing nucleus, the energy of the source radiation is modulated by using the Doppler effect, such that the emitted radiation has an energy E v) = Eo(l + vjc). For Fe the required velocities fall in the range (1 to t-1 cm s k In Mossbauer emission spectroscopy, the sample under investigation is the source, and a single line absorber is...

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. 

Mossbauer. The Mossbauer emission spectroscopy measurements were made using the Co 7 doped catalyst as a stationary source. The moving absorber was Fe enriched K4Fe(CN) -3H20. Both the Co 7 and the absorber were obtained from New England Nuclear. The con-... 

Table 7.2 Overview of Zn Mossbauer emission spectroscopy studies...

RBa2Cu40g (R = Sm, Y, Er) Nuclear-quadrupole coupling parameters at the rare-earth metal and copper sites from Cu ( Zn) and Ga( Zn) Mossbauer emission spectroscopy, EEG tensor in comparison with point charge model, shows that holes in lattices are localized primarily at chain-oxygen sites... 

HgBa2Ca iCu 02 +2 (n = 1, 2, 3) EEG tensor at the copper, barium, and mercury sites, by Cu( Zn), Ba( Cs), and Hg ( Au) Mossbauer emission spectroscopy. Comparison with point-charge approximation and Cu NMR data showed that the holes originating from defects are localized primarily in the sublattice of the oxygen lying in the copper plane (for HgBa2Ca2Cu30g, in the plane of the Cu(2) atoms)... 

Ndi g5Ceo.i5Cu04 Localization-delocalization of copper pairs on Zn impurity centers in the copper sublattice of the HTc superconductor Ndj g5Ceo.i5Cu04 was observed by Zn Mossbauer emission spectroscopy... 

Ndi g5Ceo.i5Cu04, Lao.i8Sro.i5Cu04, Possible observation of Bose condensation by Mossbauer emission spectroscopy on Cu... 

Ga( Zn) and Cu( Zn) Mossbauer emission spectroscopy on bulk GaP, GaAs and GaSb semiconductors point at isolated zinc metal centers at Ga sites. The observed center shift to higher positive velocities at the transition from p- to n-type samples corresponds to the recharging of zinc impurity centers... 

Effect of Nuclear Decay Mossbauer Emission Spectroscopy... 

The nuclear decay of radioactive atoms embedded in a host is known to lead to various chemical and physical after effects such as redox processes, bond rupture, and the formation of metastable states [46], A very successful way of investigating such after effects in solid material exploits the Mossbauer effect and has been termed Mossbauer Emission Spectroscopy (MES) or Mossbauer source experiments [47, 48]. For instance, the electron capture (EC) decay of Co to Fe, denoted Co(EC) Fe, in cobalt- or iron-containing compormds has been widely explored. In such MES experiments, the compormd tmder study is usually labeled with Co and then used as the Mossbauer source versus a single-line absorber material such as K4[Fe(CN)6]. The recorded spectrum yields information on the chemical state of the nucleogenic Fe at ca. 10 s, which is approximately the lifetime of the 14.4 keV metastable nuclear state of Fe after nuclear decay. 

Mossbauer Absorption Spectroscopy (MAS) Mossbauer Emission Spectroscopy (MES)... 

J. van de Loosdrecht, P. J. van Berge, M. W. J. Craje and A. M. van der Kraan, The application of Mossbauer emission spectroscopy to industrial cobalt based Fischer-Tropsch catalysts, Hyperfine Interact., 2002, 139/140, 3-18. 

The structural information has been provided by means of in situ Mossbauer emission spectroscopy (MES) and in situ EXAFS (for both the Mo and the Co K-edges). 

Mossbauer Measurements. Co-Mo catalysts cannot be studied directly in absorption experiments since neither cobalt nor molybdenum has suitable Mossbauer isotopes. However, by doping with 57Co the catalysts can be studied by carrying out Mossbauer emission spectroscopy (MES) experiments. In this case information about the cobalt atoms is obtained by studying the 57Fe atoms produced by the decay of 57Co. The possibilities and limitations on the use of the MES technique for the study of Co-Mo catalysts have recently been discussed (8., 25.). 

Topspe proposed that corner sites are responsible for direct sulfur extraction (A Do) (53-60), but the exact nature of corner sites is not known. What is known is that the active sites for sulfur removal constitute only about 10% of all of the Co(Ni)-Mo-S sites as identified by Mossbauer emission spectroscopy (MES) (57). Thus, there is something special about some of the Co-Mo-S sites. Further study in this area is greatly needed to clarify this issue, and it is recommended that, in the future, authors use terminology in a uniform manner. Some suggestions for standardization are made in later discussions. 

Fig. 10. Photograph and schematic representation of high-pressure Mossbauer emission spectroscopy cell 24).

A Mossbauer spectrometer consists of a radioactive Co source on a transducer that continuously scans the desired velocity range, an absorber consisting of the catalyst and a detector to measure the intensity of the gamma radiation transmitted by the absorber as a function of the source velocity. This is the common mode of operation, called Mossbauer absorption spectroscopy, sometimes abbreviated as MAS. It is also possible to fix the Co containing source and move a single-line Fe absorber, in order to investigate Co-containing catalysts. This technique, called Mossbauer emission spectroscopy (MES), has successfully been applied to study Co-Mo hydrodesulphurization catalysts [42]. 

Recently, we have found that two techniques, Mossbauer emission spectroscopy (MES) (see e.g.. Refs (6, 8-13)) and extended X-ray absorption fine structure (EXAFS) (14-16), can provide some of the needed structural information. This has not only resulted in a better description of the structural state of the catalysts but it has also allowed a better understanding of the catalytic properties. In this connection, it should be stressed that both of the above techniques conveniently allow studies to be carried out under in situ conditions. 

Time-differential Mossbauer emission spectroscopy (see Alflen et al. 1989) has also been applied to explore aftereffects. 

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