The first is called the conversion process, and at the end of this process, many energetic (excited) secondary electrons are generated. Generally, the energy-transfer processes in scintillators are understood to consist of three processes. Schematic drawings of the energy trajectories of charged particle (top) and high-energy photon (bottom) irradiations.įigure Figure3 3 represents a schematic drawing of energy transportation processes of scintillators compared with those of storage phosphors. Such a difference due to the excitation density is called the linear energy transfer (LET) effect. As schematically shown, the density of excited secondary electrons is high under charged-particle irradiation, and this high excitation density sometimes causes different physical phenomena from the case of photon excitation. Figure Figure2 2 shows schematic drawings of an ionizing photon and a charged particle interacting with various forms of matter. Although the basic phenomena are similar, a difference can be observed in the excitation density. In the case of charged particles, such as α-rays, an energetic charged particle creates many secondary electrons via some interactions such as Coulomb scattering, and these secondary electrons act in the same ways as in the case of X- and γ-rays. Finally, these secondary electrons recombine with holes and emit scintillation photons. This primary electron can generate many excited secondary electrons via Coulomb scattering, and these secondary electrons dissipate their kinetic energy by interactions with lattice or other free electrons. Photoelectric absorption is generally used to analyze the radiation, and in this process, one primary electron is generated per event. When high-energy photons, including X- and γ-rays, are absorbed by the scintillator, three interaction processes occur, which are called photoelectronic absorption, Compton scattering and pair creation. The interaction processes depend on the species of ionizing radiation and the elements of the scintillators. 2) First, the absorption of ionizing radiation energy by scintillating materials occurs. Scintillators are one of the luminescent materials that have a function to absorb ionizing radiations and to emit low-energy photons. In this paper, I focus on that scintillators and scintillation detectors. Figure Figure1 1 summarizes a classification of radiation detector materials and detector types.Ĭlassification of solid-state radiation detectors and their detector types. These storage phosphors are mainly used for personnel protection dosimetry, and in this paper I call them dosimeter materials. Semiconductors and scintillators can be applied to the both types of detectors, while storage phosphors can be applied only to the integrated type detectors with a very long integration time ( e.g., a few weeks to months). In contrast, the integrated-type detectors detect multiple events over typically a few ms so fast time-response is not required. In the counting-type detectors, because each radiation signal is processed event-by-event, a fast time-response is essentially important. From the view point of the detector types, two kinds of detection methodologies, counting-type and integration-type, are known. The number of these carriers or photons is proportional to the quantity or energy of the incident ionizing radiation thus, we can measure any ionizing radiation. 1) The former absorbs the energy of ionizing radiation and converts to a large number of carriers, while the latter converts it to a large number of photons such photons are detected by photodetectors. One is semiconductors, and the other is luminescent materials known as scintillators and storage phosphors. Such tools are often called radiation detectors there are two types of solid materials that are most commonly used for radiation detectors. In order to use such ionizing radiations, special tools are necessary to detect and visualize. Ionizing radiations are invisible to the naked eye, and some of them have a high penetration power against dense matters. Ionizing radiations have been used for many industrial and scientific purposes since their discoveries more than one hundred years ago. Classification and principles of scintillator.
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