International
Tables for
Crystallography
Volume C
Mathematical, physical and chemical tables
Edited by E. Prince

International Tables for Crystallography (2006). Vol. C, ch. 7.1, p. 619

Section 7.1.3.3. Position-sensitive detectors

W. Parrishf and J. I. Langforde

7.1.3.3. Position-sensitive detectors

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One variety of position-sensitive detector, in which the photon absorptions in different regions are counted separately, is a special type of proportional counter. The following description applies primarily to one-dimensional detectors for powder diffractometry; two-dimensional (area) detectors are treated in Section 7.1.6[link].

Position-sensitive detectors (PSD's) are being used in increasing number for various powder-diffraction studies. They have the great advantage of simultaneously recording a much larger region of the pattern than conventional counters. The difference in receiving apertures determines the gain in time. The position at which each quantum is detected is determined electronically by the system computer and stored in a multichannel analyser. There is a digital addition of each incident photon address and the angular address of the diffractometer.

The PSD's are available in short straight form and as longer detectors with curvature to match the diffractometer focusing circle. The short detectors can be used in a stationary position to cover a small angular range or scanned. Göbel (1982[link]) developed a high-speed method using a short (8° window) scanning PSD with 50 µm linear resolution in the diffractometer geometry shown in Fig. 2.3.1.12[link] (b). He was able to record at speeds of a hundred or more degrees a minute, and patterns with reasonably good statistical precision in several tens of degrees a minute. This is faster than conventional energy-dispersive diffraction and has the advantage of much higher resolution.

The PSD should be selected to match best the diffraction geometry. The detector is sensitive across the 1–2 cm gas-absorption path. If the diffracted rays are not perpendicular to the window, the parallax causes broadening and loss of resolution. This becomes important in the focusing geometries and can be minimized if the diffractometer and specimen focusing circles are nearly coincident. A large loss of resolution would occur in the conventional geometry, Fig. 2.3.1.3[link] , because only the central ray of a single reflection would be normal to the window. The problem is minimized in powder-camera geometry with a thin rod specimen, Fig. 2.3.4.1[link] (a), where the entire pattern can be recorded with a long, curved PSD (Ballon, Comparat & Pouxe, 1983[link]); see also Shishiguchi, Minato & Hashizume (1986[link]), Lehmann, Christensen, Fjellvåg, Feidenhans'l & Nielsen (1987[link]), Wölfel (1983[link]), and Foster & Wölfel (1988[link]).

References

Ballon, J., Comparat, V. & Pouxe, J. (1983). The blade chamber: a solution for curved gaseous detectors. Nucl. Instrum. Methods, 217, 213–216.
Foster, B. A. & Wölfel, E. R. (1988). Automated quantitative multiphase analysis using a focusing transmission diffractometer in conjunction with a curved position sensitive detector. Adv. X-ray Anal. 31, 325–330.
Göbel, H. E. (1982). A Guinier diffractometer with a scanning position sensitive detector. Adv. X-ray Anal. 25, 315–324.
Lehmann, M. S., Christensen, A. N., Fjellvåg, H., Feidenhans'l, R. & Nielsen, M. (1987). Structure determination by use of pattern decomposition and the Rietveld method on synchrotron X-ray and neutron powder data; the structures of Al2Y4O9 and I2O4. J. Appl. Cryst. 20, 123–129.
Shishiguchi, S., Minato, I. & Hashizume, H. (1986). Rapid collection of X-ray powder data for pattern analysis by a cylindrical position-sensitive detector. J. Appl. Cryst. 19, 420–426.
Wölfel, E. R. (1983). A novel curved position-sensitive proportional counter for X-ray diffractometry. J. Appl. Cryst. 16, 341–348.








































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