Fluorescence synchrotron source

X-ray detectors also come in several varieties (1) single-photon counters which yield accurate results but require up to several weeks to acquire the 10,000 -100,000 (lO lO ) reflections necessary to compile a complete data set for a protein crystal (2) image plates that operate much like photographic film but are 10 times more sensitive (3) area detectors, electronic devices that detect X-ray photons on a two-dimensional surface. Both fluorescent-type detectors, image plates and fast area detectors, are more sensitive at the shorter wavelengths of X-ray radiation from synchrotron sources. 

From a practical standpoint, the use of the glancing angle X-ray method, while powerful, requires a synchrotron source and therefore, due to the constraints of beam time, is necessarily limited in the number of systems that can be studied in a given time period. Of the optical methods listed, the fluorescence and resonance Raman techniques directly measure spectra of an embedded... 

Fine structure experiments are often carried out with synchrotron sources, since the initial electron state is better defined for photoemission than for electron excitation. When core-hole decay is detected by Auger or secondary electron emission, the technique is surface sensitive. Core-hole decay can also be detected by fluorescence, or by adsorption of the incident photon beam. These methods are not intrinsically surface sensitive, but they are useful when the source atoms are exclusively located at the surface. 

In section 2, the different theoretical models for local dynamics are briefly reviewed, and their connection with spectroscopic experiments is recalled. The Fluorescence Anisotropy Decay technique and the synchrotron source are presented in section 3. The fourth section is concerned with two typical examples. Using a series of experiments performed on polystyrene dilute solutions and another one performed on melt poly butadiene, we show how the different theoretical models can be told apart, and we present new information about the processes responsible of backbone rearrangement which has been obtained using the cyclosynchrotron LURE-ACO at Orsay (France). 

All these characteristics allow to measure FAD with a statistic quality and a reliability out of reach of flash sources. Moreover, in the case of polymers, it is generally not possible to purify samples as much as one would wish to perform a fluorescence experiment in comfortable conditions, and the free choice of wavelength permitted by the continuous spectrum of the synchrotron source is essential. In this regard, lasers, which also provide very intense and short light pulses usable for fluorescence experiments somewhat less flexible. This may partly explain... 

The high-intensity and collimated nature of beams from a synchrotron source leads to applications that cannot be accomplished by the other three X-ray sources. For a review of the applications of synchrotron-induced X-rays, see K. W. Jones and B. M. Gordon. Anal. Chem., 1989,6i. 341 A for a discussion of the use of total-reflectance X-ray fluorescence induced by synchrotron radiation, see K. Baur, S. Brennan. P. Pianetta, and R. Opila, Anal. Chem, 2002. 74. 608A. 

Laser ablation for solid sampling X-ray fluorescence analysis with synchrotron source (XRF)... 

In this paper we first describe briefly the fluorescence anisotropy decay method and the equipment necessary and we emphasize the advantages of synchrotron sources. We will indicate several chemical reactions which can be used to label a polymer. Then, we will present and discuss typical examples of fluorescence anisotropy decay studies on dilute and concentrated polymer solutions and on bulk polymers. 

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