Scintillator materials for x-ray detectors and beam monitors
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Introduction Ionizing radiation-to-visible-light converters, called scintillators, are essential in x-ray imaging, x-ray beam monitoring, and x-ray counter applications, and are deployed for hard x-ray energy applications. The main advantages of indirect detectors, which consist of a scintillator and a photon detector, are that they cover a range of pixel sizes, from 100 nm to millimeter size, they can be used for time-resolved experiments, and they are radiation hard (resistant). An additional advantage is that they represent an efficient way to detect x-rays up to 100 keV or more in energy and can handle very high fluxes. Figure 1 shows examples of scintillators and their optical coupling; Table I lists these components and their dimensions. For additional information, please see Table SI, available online. The use of high x-ray energy or high flux requires specific optomechanical engineering design. One example is to remove the optics from the direct x-ray path as shown in Figure 2.1
Characteristics of the scintillating material The desired characteristics of scintillators are strongly dependent on the application for which they are used. In the case of x-ray imaging, the required characteristics include the following: • X-ray absorption: Maximize the x-ray stopping power by the couple ρ.Zeff, where ρ and Zeff are the density and effective atomic number of the scintillator, respectively.
• Light emission: High conversion efficiency (>15 photons/ keV), where the emission wavelength of the scintillator must match the spectral sensitivity of the imaging sensor and the flux must match the dynamic range. • Timing: Time-resolved experiments require fast decay time (
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