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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. 7.1, p. 631
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The incoming X-rays are converted to light in a phosphor that is coupled to the first photocathode of the system. Both polycrystalline and monocrystalline phosphors are used for X-ray detection. The former give a higher light output but have a limited resolution; the latter tend to have a poorer light-conversion efficiency but have the best resolution. The most useful phosphors are shown in Table 7.1.6.2![[link]](/graphics/greenarr.gif)
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Many attempts have been made to improve the spatial resolution of phosphor screens by constructing them in the form of scintillating fibres that are optically isolated from one another so that the scintillation does not spread. This can be achieved by growing columnar scintillating crystals (Oba, Ito, Yamaguchi & Tanaka, 1988), by intagliating polycrystalline phosphors (Fouassier, Duchenois, Dietz, Guillemet & Lemonnier, 1988) and by using arrays of scintillating fibres (Bigler, Polack & Lowenthal, 1986; Ikhlef & Skowronek, 1993, 1994).
Image intensifiers designed for radiography with relatively hard radiation usually have an X-ray-transparent window – which may be up to 300 mm in diameter – and an internal phosphor–photocathode sandwich deposited on an X-ray-transparent substrate. Problems of compatibility of phosphor and photocathode have restricted the phosphor used, but CsI works well with multialkali photocathodes. Moy and his collaborators have constructed a large-diameter television detector in which the image intensifierhas been modified by using beryllium for the window and for the sandwich substrate; this intensifier is coupled to a slow-scan CCD camera (Moy, 1994).
References
Bigler, E., Polack, F. & Lowenthal, S. (1986). Scintillating fibre array as an X-ray image detector. Proc. SPIE, 733, 133–137.Google Scholar
Fouassier, M., Duchenois, V., Dietz, J., Guillemet, E. & Lemonnier, M. (1988). Image intensifier tubes with intagliated screens. Adv. Electron. Electron Phys. 74, 315–322.Google Scholar
Ikhlef, A. & Skowronek, M. (1993). Radiation position-sensitive detector based on plastic scintillating fibres. Rev. Sci. Instrum. 61, 2566–2569.Google Scholar
Ikhlef, A. & Skowronek, M. (1994). Some emission characteristics of scintillating fibres for low-energy X- and Y-rays. IEEE Trans. Nucl. Sci. NS-41, 408–414.Google Scholar
Moy, J.-P. (1994). A 200 mm input field 5–80 keV detector based on an X-ray image intensifier and CCD camera. Nucl. Instrum. Methods, A348, 641–644.Google Scholar
Oba, K., Ito, M., Yamaguchi, M. & Tanaka, M. (1988). A CsI(Na) scintillation plate with high spatial resolution. Adv. Electron. Electron Phys. 74, 247–255.Google Scholar
