Area detector for X-rays

Cork, C., Hamlin, R., Vernon, W. and Xuong, N. H. (1975). Xenon-fhled multiwire area detector for X-ray diffraction. Acta Crystallogr. A 31, 702-703. 

Archaeobacteria 7, 815 Area detector for X-rays 134 Arg-Gly-Asp (RGD) sequence 408 Arginase 888... 

In this paper a new design for a high-energy 3D-CT scanner equipped with a linear accelerator as radiation source and an area high-energy x-ray detector is presented. This system is the extension of a 2D system which is installed at present time [3,4]. 

In many applications full two-dimensional information is necessary, and thus fast read-out systems have to be provided. The various techniques, which have been discussed before, have been applied with area detectors. The delay-line read-out has been used with two-dimensional detectors in synchrotron radiation laboratories. At the DORIS-ring in Hamburg an area detector with a 1 mm anode wire distance and a total area of 200 mm x 200 mm is currently in use for measurements of muscle diffraction patterns and for X-ray crystallography The spatial resolution is about (2,5x2,5)mm FWHM. 

The most frequently used silicon detector is a small pellet of lithium drifted silicon, some 6 mm in diameter and 3-4 mm thick. It is good only for X-rays, in the energy range between 4 and 50 keV. In fact, there are some standard sizes of Si(Li) detectors, areas of 30 and 100 mm are considered normal, anything else is a detector made by specifications of the user. 

A further increase in speed of data taking is expected by segmentation of detectors, i.e. each detector segment has its own read-out system. A linear position-sensitive detector develop recently at EMBL consists of 128 anode wires, with each of them acting as an individual counter. The integral count rate is 10 MHz of statistical events. A similar development has been started for area counters. The new diffractometer for X-ray resonance scattering in HASYLAB is equipped with three area counters (Fig. 5). This system can handle nearly a million statical events per second... 

Overall, therefore, the introduction of CCD area detectors for laboratory X-ray diffraction has provided an opportunity to determine structures from samples that were previously not feasible or impractical (crystals too small or twinned). In addition, data quality and therefore structure quality have improved and data collection times have decreased. To organometallic chemists, who often rely upon crystal structure determination to characterize new and unusual ligand bonding where unambiguous spectroscopic characterization is difficult or impossible, this change is a great step forward. 

Up to this point, two distinct types of specimen, single crystals and polycrystalline powders, have been discussed. In the analysis of a single crystal, it is essential that the specimen contains no polycrystalline material in polycrystalline powders. one condition for X-ray examination is that the directions of the net planes have a uniform statistical distribution in space, otherwise more or less complicated corrections must be applied, perhaps by preparation or by computer programs. An intelligent use of preferred orientation for structure analysis is recording the diffraction diagram by an area detector. The reflections are partly spread out into two dimensions, many more reflections are resolved, more reflections can be used for determining the cell constants, and overlap of intensities of reflections is diminished [116]. 

Figure 2 shows an SEM of the silicone distribution on PAS films by EPMA. The silicon units are indicated as white areas when the X-ray detector is set to the wavelength for silicon. It was obvious that the white areas increased with increasing PDMS content in PAS. From this result, it seems that the silicone and aramid blocks underwent microphase separation. To determine the microphase separation of PAS, more data were needed. The... 

Due to large improvements in computer technology in combination with new designs of area x-ray detector systems it is possible to extend the 2D-CT systems up to the third dimension. Therefor special algorithms and techniques for 3D-CT of the measured projection data and 3D visualisation and measurement of the results had to be developed. 

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