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Industrial Radiography
Published in Paolo Russo, Handbook of X-ray Imaging, 2017
These charge carriers may be trapped at impurity sites, such as electrons at a halogen vacancy (F-center) or holes at an interstitial Br2+ molecule (H-center). Red laser light (600–700 nm) excites electrons trapped in a Br− vacancy (FBr-center) to a higher state from which they may tunnel and recombine with a nearby trapped hole. Transfer of the recombination energy excites a nearby located Eu2+ ion. Upon return to its ground state, this Eu2+ ion emits a blue photon (390 nm). This process is described as photostimulated luminescence (PSL).
Light-induced fading of the photostimulated luminescence and thermoluminescence for irradiated silicate samples
Published in Radiation Effects and Defects in Solids, 2023
Ivana Sandeva, Hristina Spasevska, Margarita Ginovska, Lihnida Stojanovska-Georgievska, Slobodan Masic
Detection methods for irradiated food, according to the changes they detect, are classified into three main groups: biological, chemical and physical methods.[5] The ideal method for detection should measure a specific effect of the ionizing radiation, which is not dependent on the processing and storage of food and the length of time between treatment and testing.[6] Physical methods are based on the detection of physical changes.[7] One simple physical method for the detection of irradiated food is optically stimulated luminescence or photostimulated luminescence (PSL). Samples are stimulated with pulsed infra-red radiation, and the signal is detected at the end of each pulse. This method gives reliable results for foodstuffs that contain a sufficient amount of minerals. This method is usually confirmed by measurements with thermoluminescence, in which samples are stimulated with heat instead of optical stimulation. The bases of these methods are the characteristics of minerals found in food. Minerals store energy in the defects of their crystal lattice by exposure to ionising radiation. That is, ionising radiation excites electrons that can be trapped in the imperfections of the lattice. When these electrons gain energy by optical or thermal stimulation, they recombine with holes and photons are emitted. That is why it is important for the analysed samples to contain minerals. The optical or thermal stimulation is responsible for the release of electrons that have been trapped in the lattice. When these electrons return from the excited state to the ground state, they lose part of their energy as photons, thus a signal could be observed and measured as a luminescence response.