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International
Tables for Crystallography Volume C Mathematical, physical and chemical tables Edited by E. Prince © International Union of Crystallography 2006 |
International Tables for Crystallography (2006). Vol. C. ch. 4.1, p. 189
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X-ray beams from rotating-anode tubes are approximately one hundred times more intensive than those from normal X-ray tubes. Laser plasma X-ray sources yield intensive nanosecond pulses of the line spectrum of nearly electron-free ions in the X-ray region with a spectral breadth of ![[\Delta\lambda/\lambda\approx10^{-3}.]](/teximages/cbch4o1/cbch4o1fi26.svg)
Several such pulses may be repeated per hour (Frankel & Forsyth, 1979![[link]](/graphics/greenarr.gif)
). Synchrotron radiation is characterized by a continuous spectrum of wavelengths, high spectral flux, high intensity, high brightness, extreme collimation, sharp time structure (pulses with 30–200 ps length emitted in ns intervals), and nearly 100% polarization in the orbital plane (Kunz, 1979; Bonse, 1980). Some of these properties are utilized in ordinary structure analysis: for example, fine tuning of the wavelength of synchrotron radiation for the solution of the phase problem by resonant scattering on chosen atomic species constituting the material under study. But these radiations also offer new advantages in other fields of crystallography, as, for example, in X-ray topography (Tanner & Bowen, 1980), in time-resolving studies (Bordas, 1980), in X-ray microscopy (Parsons, 1980), in studies of local atomic arrangements by extended X-ray absorption fine structure (XAFS) investigations (Lee, Citrin, Eisenberger & Kincaid, 1981) or studies of surface structures by X-ray photoemission spectroscopy (XPS) (Plummer & Eberhardt, 1982), etc. γ-rays emitted by radioactive sources such as 198Au (t1/2 = 2.7 d), 153Sm (t1/2 = 46.8 h), 192Ir (t1/2 = 74.2 d) or 137Cs (t1/2 = 29.9 a) are characterized by short wavelengths (typically hundreds of Å), by narrow spectral breadth ![[(\Delta E\approx10^{-8}\ {\rm eV},\Delta\lambda/\lambda\approx10^{-6})]](/teximages/cbch4o1/cbch4o1fi27.svg)
and by relatively low beam intensity (∼108–109 m−2 s−1). They are mainly used for studies of the mosaic structure of single crystals (Schneider, 1983) or for the determination of charge density distribution (Hansen & Schneider, 1984). The typical absorption length of ∼1–4 cm and the increase of the extinction length by a factor of about 50 compared with ordinary X-rays are advantages utilized in these experiments. γ-rays also find applications in magnetic structure studies and in the determination of gradients of electric fields by Mössbauer diffraction and spectroscopy (Kuz'min, Kolpakov & Zhdanov, 1966).
For Compton scattering, see Sections 6.1.1
and 7.4.3
.
References
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