Fluorescence resonance

Preparation of Mossbauer Source 19.7.4. Atmospheric Aerosol Samples. 576 

Since the discovery of the Mossbauer effect by Rudolf MSssbauer [1]-[3] in 1958 this nuclear spectroscopic method has found a wide variety of applications in materials science, solid state physics. chemistry, metallurgy, and earth sciences. 

Up to the present time, the Mossbauer effect has been observed for almost 100 nuclear transitions in more than 40 different elements. Not all of these transitions are suitable for actual studies, for reasons that will be discussed below. But ca. 15-20 elements remain that are appropriate for applications, of which the best known Mossbauer nuclide is iron, because on the one hand the Mbss-bauer experiment is easy to perform with the 14.4 keV transition in Fe. and on the other hand the element iron is very abundant in nature. 

It is the purpose of this article to introduce the reader unfamiliar with the field to the principles of Mossbauer spectroscopy, and to the various types of chemical information that can be extracted from 

Principle and Experimental Conditions of Recoil-free Nuclear Resonance Fluorescence 

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Mosshauer effect The resonance fluorescence by y-radiation of an atomic nucleus, returning from an excited state to the ground state. The resonance energy is characteristic of the chemical environment of the nucleus and Mossbauer spectroscopy may be used to yield information about this chemical environment. Used particularly in the study of Fe. Sn and Sb compounds. 

R. Hanbury Brown, R., Twiss, R.Q., 1956, Correlation between photons in two coherent beams of light. Nature 177, 27 Hong, C.K., Ou, Z.Y., Mandel, L., 1987, Measurement of subpicosecond time intervals between two photons by interference, Phys. Rev. Lett. 59, 2044 Kimble, H.J., Dagenais, M., Mandel, L., 1977, Photon Antibunching in Resonance Fluorescence, Phys. Rev. Lett. 39, 691... 

Resonant y-ray absorption is directly connected with nuclear resonance fluorescence. This is the re-emission of a (second) y-ray from the excited state of the absorber nucleus after resonance absorption. The transition back to the ground state occurs with the same mean lifetime t by the emission of a y-ray in an arbitrary direction, or by energy transfer from the nucleus to the K-shell via internal conversion and the ejection of conversion electrons (see footnote 1). Nuclear resonance fluorescence was the basis for the experiments that finally led to R. L. Mossbauer s discovery of nuclear y-resonance in ir ([1-3] in Chap. 1) and is the basis of Mossbauer experiments with synchrotron radiation which can be used instead of y-radiation from classical sources (see Chap. 9). 

Principles and Characteristics Atomic fluorescence spectrometry (AFS) is based on excitation of atoms by radiation of a suitable wavelength (absorption), and detection and measurement of the resultant de-excitation (fluorescence). The only process of analytical importance is resonance fluorescence, in which the excitation and fluorescence lines have the same wavelength. Nonresonance transitions are not particularly analytically useful, and involve absorption and fluorescence photons of different energies (wavelength). 

Atkinson Pitts Jr. 1977 quoted, Gaffney Levine 1979) k0H = 5.07 x 10-11 cm3 molecule-1 s-1 at 297.2 K, measured range 297 125 K (flash photolysis-resonance fluorescence, Atkinson Pitts 1977)... 

Beattie, I.R., Ozin, G.A., and Perry, R.O., Gas phase Raman spectra of P4, P2, As4 and As2. Resonance fluorescence spectrum of 80Se2. Resonance fluores-cence-Raman effects in the gas-phase spectra of sulfur and iodine. Effect of pressure on the depolarization ratios for iodine,. Chem. Soc., Perkin I, 2071, 1970. 

The reactions of the ground-state oxygen atom 0(3P) with symmetric aliphatic ethers in the gas phase were investigated by Liu et al. (1990) using the flash photolysis resonance fluorescence technique. These reactions were found to be first-order with respect to each reactant. The rate constants for three ethers at several temperatures are as follows ... 

AFS quantifies the discrete radiation emitted by excited state atoms that have been excited by radiation from a spectral source. There are a number of mechanisms that are responsible for the atomic fluorescence signal resonance fluorescence, step-wise fluorescence, direct-line fluorescence, and sensitized fluorescence. Generally, the lowest resonance transition (l->0) is used for AFS. If a line source is used for excitation and if the atomic vapor is dilute, then the radiant power of the atomic... 

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