Direct Calibration for a Synchrotron Beamline

Direct calibration to absolute intensity is not a usual procedure at synchrotron beamlines. Nevertheless, the technical possibilities for realization are improving. Therefore the basic result for the total scattering intensity measured in normal transmission geometry is presented. At a synchrotron beamline point-focus can be realized in good approximation and the intensity 7(s) is measured. Then integration of Eq. (7.19) results in 

Cylindrical Filaments. If cylindrical filaments are studied, the last-mentioned assumption is not be fulfilled. In this case it is more suitable to cross an elongated primary beam and the fiber in such a way that the irradiated height of the beam, Bbo, is constant. Then the irradiated volume becomes V = BsoJtrj, with r/ being the radius of the fiber. In many practical applications the studied fiber is very thin, and the effective absorption coefficient can be approximated by exp —fiteff) 1. If this approximation is not feasible, the absorption factor exp(—/j. ) must be integrated for the chord length distribution gc ( ) of a circle with radius r/ (cf. p 168) in order to yield the effective absorption. 

Protection of the Detector. With all direct calibration methods the primary beam intensity must be measured. If the primary beam itself is attenuated, shape of the beam and spectral composition of the radiation may be altered. This problem is avoided if the load of the detector is reduced by scanning the beam using a slit or a perforated disc. On the other hand, in order to be useful at a powerful synchrotron beamline these devices should have very tiny and well-defined slits or holes. 

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