Scintillation detector optical coupling

Figure 10.6 Schematic diagram of a scintillation detector comprising a scintillation crystal optically coupled to a photomultiplier tube...

The typical complete scintillation gamma-ray detector is shown in Figure 10.8, with the scintillator crystal optically coupled (of which more later) to the photomultiplier tube. 

A sealed-tube neutron generator, utilizing the deuterium-tritium reaction is the source of fast (14 MeV) neutrons, and a 8 x 3 1 Nal scintillation detector, with three optically coupled photomultipliers, is used to measure the >ray signal... 

The secondary electrons emitted from the sample are attracted to the detector by the collector screen. Once near the detector, the secondary electrons are accelerated into the scintillator by a positive potential maintained on the scintillator. Visible light is produced by the reaction of the secondary electrons with the scintillator material. The emitted light is detected by a photomultiplier tube, which is optically coupled to the scintillator via a light pipe. The PMT signal is then transferred to the grid of a cathode ray tube (CRT). Data collection... 

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... 

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. 

Although direct coupling of a camera to a scintillator can give acceptable results one of its major drawback is the degradation of the quantum noise mainly related to the low transmission of the optics. The following schematics summarizes the particles flux (photons and electrons) across the different stages of the detector ... 

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