Gamma resonance absorption

The Mossbauer effect, discovered by Rudolf L. Mossbauer in 1957, can in short be described as the recoil-free emission and resonant absorption of gamma radiation by nuclei. In the case of iron, the source consists of Co, which decays with a half-life of 270 days to an excited state of Fe (natural abundance in iron 2%). The latter, in turn, decays rapidly to the first excited state of this isotope. The final decay generates a 14.4 keV photon and a very narrow natural linewidth of the order of nano eV. 

Mossbauer spectroscopy involves the measurement of minute frequency shifts in the resonant gamma-ray absorption cross-section of a target nucleus (most commonly Fe occasionally Sn, Au, and a few others) embedded in a solid material. Because Mossbauer spectroscopy directly probes the chemical properties of the target nucleus, it is ideally suited to studies of complex materials and Fe-poor solid solutions. Mossbauer studies are commonly used to infer properties like oxidation states and coordination number at the site occupied by the target atom (Flawthome 1988). Mossbauer-based fractionation models are based on an extension of Equations (4) and (5) (Bigeleisen and Mayer 1947), which relate a to either sums of squares of vibrational frequencies or a sum of force constants. In the Polyakov (1997)... 

In addition to the 9.17 MeV photon transmission, the NRA approach needs a background gamma measurement to assist in compensating for the mass-dependent attenuation (non-resonant absorption) of the photons in the cargo. Prototype NRA... 

Morgado et al., The Effects of Proton Beam Quality on the Production of Gamma Rays For Nuclear Resonance Absorption in Nitrogen, in Substance Detection Systems, G.L. Harding, R. C. Lanza, and L.J. Myers, Editors, Proceedings SPIE 2092, (1994) 503. 

D. Vartsky, G. Engler, M. B. Goldberg, R. A. Krauss, A Method for Detection of Explosives Based on Nuclear Resonance Absorption of Gamma Rays in 14N, SPIE, Vol. 2092, Substance Detection Systems (1993) 307. 

Impulseless resonance absorption of y-quants (gamma radiation) from a radioactive isotope, here Cobalt 57Co 57Fe + y (main quant 122 keV quant used for spectroscopy has a different energy)... 

The spectrum shown in Figure 4.55 is obtained when there are no hyperhne interactions, that is, the emitter and the absorber have the same energy of emission and absorption. Consequently, the maximum absorption of gamma photons emitted by the source at the thin absorber is v = 0, because of resonant absorption. Subsequently, as the velocity of the source is increased in the positive or the negative directions, the resonance is broken and, therefore, the transmission of gamma photons through the absorber increases [135],... 

Microwave-based meters have also been used to monitor water content in emulsions (39). Microwave techniques can be used in two ways Either the attenuation of the microwave radiation due to absorption by the water phase is measured, or capacitance or resonance changes in a microwave cavity are noted. The capacitance-change method is much more sensitive, although both, like the gamma-ray absorption method, are limited in that solids content must be constant or zero in order to accurately interpret the information obtained. Both of these techniques are applicable to field situations and on-line monitoring. 

Mossbauer effect Resonance absorption of gamma radiation by specific nuclei arranged in a crystal lattice in such a way that the recoil momentum is shared by many atoms. It is the basis of a form of spectroscopy used for studying coordinated metal ions. The principal application in bioinorganic chemistry is 57Fe. The parameters derived from the Mossbauer spectrum (isomer shift, quadrupole splitting, and the hyperfine cou-... 

Mossbauer spectroscopy measures the resonant absorption of nuclear gamma rays involved with transitions between the ground and excited states of atomic nuclei with nonzero angular momenta. The precise energy of such transitions is... 

R. L. Mossbauer (Munich) resonance absorption of gamma radiation and discovery of the effect which bears his name. 

Very similar information can be obtained with the experimentally less demanding Mossbauer spectroscopy. The resonant absorption of gamma radiation by certain atomic nuclei ( Fe, Sn and several other isotopes of technical interest, e.g. Co, can also be studied in the emission mode) yields information about the electromagnetic environment of this atom. By comparison with standard samples the chemical environment of a given atom, the specific type of chemical compound wherein it is incorporated and further morphological information can be derived Irom the Mossbauer spectra [104-113]. 

The source most commonly employed with Fe Mossbauer spectroscopy is elemental Co, which is incorporated into rhodium or copper metal. During the radioactive decay of the cobalt isotope into Fe, the needed gamma radiation is emitted. For measurements with tin ( Sn), sources of CaSnOs or BaSnOs enriched with Sn are used, which again release the proper radiation during their radioactive decay. The source is moved at constant positive and subsequently negative accelerations (i.e. linearly varying speed) to probe the resonant absorption. 

The MOssbauer effect is the resonant absorption of y-rays. Gamma emission occurs when a nucleus drops from an excited state to one of lower energy. If these now fall on a nucleus of the same iso-... 

For his researches concerning the resonance absorption of gamma radiation and his discovery in this connection of the effect that bears his name... 

Such method excludes the uncontrolled influence of reverse scattering of resonant gamma quanta after changing resonant absorption to nonresonant (which would occur when resonant absorber cylinder is simply taken off the source). Each measurement lasted At= 100s. The results of measurements are presented in Fig. 14.6. 

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