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Absorber, Mossbauer spectroscopy

An important accessory in many applications of Mossbauer spectroscopy is a cryostat for low temperature and temperature-dependent measurements. This may be necessary to keep samples frozen or to overcome small Debye-Waller factors of the absorbers at room temperature in the case of an isotope with high y-energy. Paramagnetic samples are measured at liquid-helium temperatures to slow down... [Pg.41]

Fig. 3.19 Schematic illustration of the measurement geometry for Mossbauer spectrometers. In transmission geometry, the absorber (sample) is between the nuclear source of 14.4 keV y-rays (normally Co/Rh) and the detector. The peaks are negative features and the absorber should be thin with respect to absorption of the y-rays to minimize nonlinear effects. In emission (backscatter) Mossbauer spectroscopy, the radiation source and detector are on the same side of the sample. The peaks are positive features, corresponding to recoilless emission of 14.4 keV y-rays and conversion X-rays and electrons. For both measurement geometries Mossbauer spectra are counts per channel as a function of the Doppler velocity (normally in units of mm s relative to the mid-point of the spectrum of a-Fe in the case of Fe Mossbauer spectroscopy). MIMOS II operates in backscattering geometry circle), but the internal reference channel works in transmission mode... Fig. 3.19 Schematic illustration of the measurement geometry for Mossbauer spectrometers. In transmission geometry, the absorber (sample) is between the nuclear source of 14.4 keV y-rays (normally Co/Rh) and the detector. The peaks are negative features and the absorber should be thin with respect to absorption of the y-rays to minimize nonlinear effects. In emission (backscatter) Mossbauer spectroscopy, the radiation source and detector are on the same side of the sample. The peaks are positive features, corresponding to recoilless emission of 14.4 keV y-rays and conversion X-rays and electrons. For both measurement geometries Mossbauer spectra are counts per channel as a function of the Doppler velocity (normally in units of mm s relative to the mid-point of the spectrum of a-Fe in the case of Fe Mossbauer spectroscopy). MIMOS II operates in backscattering geometry circle), but the internal reference channel works in transmission mode...
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. [Pg.148]

Nevertheless, Mossbauer spectroscopy is sensitive to the core region of the absorber and therefore, it is of interest to investigate how the radial expectation values are influenced by relativity. This will be further elaborated here. [Pg.149]

The precursor of ° Ru is ° Rh (tip, = 3 years). It is prepared by irradiating natural ruthenium metal with 20 MeV deuterons, " Ru (d, n) Rh. The target is then allowed to decay for several months to diminish the accompanying Rh activity. In a report on ° Ru Mossbauer spectroscopy [111], the authors reported on spectra of Ru metal, RuOa, and [Ru(NH3)4(HS03)2] at liquid helium temperature in standard transmission geometry using a Ge(Li) diode to detect the 127 keV y-rays. The absorber samples contained 1 g of ruthenium per cm. ... [Pg.270]

Mossbauer spectroscopy with started only in 1965, when Harris et al. [322] measured the Mossbauer absorption spectra of the 99 keV transition of Pt in platinum metal as a function of temperature (between 20 and 100 K) and of absorber thickness and derived the temperature dependence of the Debye-Waller factor. [Pg.339]

Mossbauer spectroscopy is an analytical technique that, in archaeological ceramic studies, provides information on the condition and characteristics of the compounds of iron in pottery. Using the technique makes it possible to determine the relative amounts of the different (ferrous and ferric) ions of iron and hence to ascertain the firing conditions of the pottery at the time it was made. The technique involves irradiating a sample of pottery with gamma rays and then assessing the amount of radiation absorbed by the nuclei of the ions of iron within the pottery (Feathers et al. 1998 Bearat and Pradell 1997). [Pg.60]

The most direct information on the state of cobalt has come from Mossbauer spectroscopy, applied in the emission mode. As explained in Chapter 5, such experiments are done with catalysts that contain the radioactive isotope 57Co as the source and a moving single-line absorber. Great advantages of this method are that the Co-Mo catalyst can be investigated under in situ conditions and the spectrum of cobalt can be correlated to the activity of the catalyst. One needs to be careful, however, because the Mossbauer spectrum one obtains is strictly speaking not that of cobalt, but that of its decay product, iron. The safest way to go is therefore to compare the spectra of the Co-Mo catalysts with those of model compounds for which the state of cobalt is known. This was the approach taken... [Pg.272]

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-... [Pg.8]

The [Fe =0(TMP+ )]+ complex exhibited a characteristic bright green color and corresponding visible absorbance in its UV-vis spectrum. In its NMR spectrum, the meta-proton doublet of the porphyrin mesityl groups were shifted more than 70 ppm downfield from tetramethylsilane (TMS) because they were in the presence of the cation radical, while the methyl protons shift between 10 and 20ppm downfield. In Mossbauer spectroscopy, the isomer shift, 5 of 0.06 mm/s, and A q value of 1.62mm/s were similar to those for other known Fe(IV) complexes. Electron paramagnetic resonance (EPR), resonance Raman (RR), and EXAFS spectroscopies provided additional indications of an Fe =0 n-cation radical intermediate. For instance,... [Pg.376]

Mossbauer spectroscopy is based on transition between energy levels of nuclei with different values of the nuclear spin quantum number /. When a nucleus emits a y-ray, the energy of the emitted radiation is lowered by the recoil of the nucleus. Conversely, the energy needed for absorption is higher than that needed for transition, because the absorbing nucleus absorbs energy in the recoil process. For nuclei tightly bound in solids, however, the effective mass of the emitter and... [Pg.221]

Most often the transmission mode is found to be the most convenient in Mossbauer spectroscopy, i.e., the y radiation passes from the source through the absorber, and the attenuation of the primary beam is measured at the various Doppler velocities. However, there are a number of cases where a "scattering geometry may be advantageous (SO). The basis for this geometry lies in those processes that take place after resonant absorption of y radiation by the Mossbauer isotope. Specifically, after excitation the Mossbauer isotope may reemit the y ray, or it may decay by emission of internal conversion electrons and X rays [with the probability of internal conversion equal to a/(l + a)]. [Pg.162]

In 1957, Rudolph Mossbauer, during his graduate studies, discovered an outstanding effect [49] that has generated an entire field in physics, that is, a very high-resolution spectroscopy in the y-ray region of the spectrum named Mossbauer spectroscopy [50-56], The effect consists of the fact that a y photon emitted by an excited nucleus can be resonantly absorbed by another nucleus [50-56], This means that a recoilless emission and absorption has occurred. [Pg.58]


See other pages where Absorber, Mossbauer spectroscopy is mentioned: [Pg.310]    [Pg.344]    [Pg.310]    [Pg.344]    [Pg.501]    [Pg.21]    [Pg.39]    [Pg.41]    [Pg.186]    [Pg.256]    [Pg.260]    [Pg.292]    [Pg.334]    [Pg.60]    [Pg.343]    [Pg.109]    [Pg.404]    [Pg.91]    [Pg.9]    [Pg.37]    [Pg.185]    [Pg.410]    [Pg.536]    [Pg.157]    [Pg.3]    [Pg.4]    [Pg.4]    [Pg.5]    [Pg.9]    [Pg.57]    [Pg.255]    [Pg.277]    [Pg.126]    [Pg.305]    [Pg.393]    [Pg.260]    [Pg.94]   
See also in sourсe #XX -- [ Pg.564 , Pg.567 ]




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