Scintillation Detector Array

FIGURE 9.5 Arrangement of dectectors around a cylindrical fluidized bed 

FIGURE 9.6 Schematic diagram of the signal-processing instruments and data acquisition system 

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The Phoswich Detector System (PDS) consists of a square array of four independent NaI(Tl)/CsI(Na) phoswich scintillation detectors. Each of the four detectors is made of two crystals of Nal(Tl) and CsI(Na) optically coupled and forming what is known as PHOSWICH (acronym of PHOsphor and semdWICH). The scintillation light produced in each phoswich is viewed, through a light guide of quartz, by a photomultiplier tube (PMT). The Nal(Tl) acts as X-ray detector, while the CsI(Na) scintillator acts as an active shield. 

The detector geometry used is a 3 layer design, with a semiconductor array top layer, and two lower layers which are scintillator/photodiode arrays. The semiconductor layer is made of CdTe 2mm thick and the scintillator arrays are 3cm of CsI(Tl). All the pixels are hexagonal with an across flats dimension of 11mm and a centre to centre spacing of 11.75mm. The detector is surrounded on all sides, and on the bottom by a 2cm thick BGO veto crystal. 

Figure 3 shows the percentage of detected mispositioned events in different scintillator with different size, when the photons irradiated perpendicular to central pixel of detector array. Percentage of detected photons in one of the adjacent pixel in crystal array is illustrated In Figure 4. As it can be seen, quantitative variations of detected photons are negligible for 0 to 10 degree.

For the parallel recording of EEL spectra in STEM, linear arrays of semiconductor detectors are used. Such detectors convert the incident electrons mto photons, using additional fluorescent coatings or scintillators in the very same way as the TEM detectors described above. 

Detectors are used to convert X-ray flux into an electrical signal, which can then be digitized and stored. For imaging cabinet X-ray systems, the detectors usually consist of a folded linear array of scintillators optically coupled to photodiodes. Typically, 500-1000 such detector elements are present for single-energy imaging... 

Radiation scattered from the inspection point, after passing thru the detector collimator, impinges on scintillators which convert this incident radiation to visible light. The visible light, in turn, is sensed by an array of photomultiplier tubes that generate electrical outputs which are directed to computers for data reduction and analysis. These signals are proportional to the density of the HE in the shell... 

A redundant medical PET scanner, a CTI ECAT931/08, was acquired. This comprises 128 detector blocks (Figure 2a), each consisting of four photomultiplier tubes viewing a 30 mm thick crystal of bismuth germanate scintillator approximately 49 x 56 mm2 in area, which is cut into an array of 8 x 4 elements (each approximately 5.6 x 12.9 mm2,... 

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