Line and area detectors

A position sensitive detector (PSD) employs the principle of a gas proportional counter, with an added capability to detect the location of a photon absorption event. Hence, unlike the conventional gas proportional counter, the PSD is a line detector that can measure the intensity of the diffracted beam in multiple (usually thousands) points simultaneously. As a result, a powder diffraction experiment becomes much faster, while its quality generally remains nearly identical to that obtained using a standard gas proportional counter.  

A significant deterioration of the quality of x-ray powder diffraction data may occur when the studied specimen is highly fluorescent because it is impractical to monochromatize the diffracted beam when using line or area detectors. Also see Chapter 3. 

Area detectors record diffraction pattern in two dimensions simultaneously. Not counting the photographic film, two t)q)es of electronic area detectors have been advanced to a commercial status, and are becoming more frequently used in modem x-ray powder diffraction analysis. 

A typical CCD phosphor is Tb doped Gd202S, which converts x-ray photons into visible light photons. 

A typical image plate phosphor is doped BaFBr. When exposed to x-rays, oxidizes to Eu. Thus produced electrons may either recombine with Eu or they become trapped by F-vacancies in the crystal lattice of BaFBr. The trapped electrons may exist in this metastable state for a long time. They are released when exposed to a visible light and emit blue photons during recombination with Eu ions, e.g. see K. Takahashi, K. Khoda, J. Miyahara, Y. Kanemitsu, K. Amitani, and S. Shionoya, Mechanism of photostimulated luminescence in BaFX Eu (X = Cl, Br) phosphors, J. Luminesc. 31-32,266 (1984). 

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