For an incident gamma-ray interacting with an inorganic scintillator, describe the interaction of the gamma-ray, how scintillation...

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Chemistry

For an incident gamma-ray interacting with an inorganicscintillator, describe the interaction of the gamma-ray, howscintillation light is generated, how it is converted into anelectrical signal, and how it is amplified.

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Gamma rays HighZ materials eg inorganic crystals are best suited for the detection of gamma rays The three basic ways that a gamma ray interacts with matter are the photoelectric effect Compton scattering and pair production The photon is completely absorbed in photoelectric effect and pair production while only partial energy is deposited in any given Compton scattering The cross section for the photoelectric process is proportional to Z5 that for pair production proportional to Z2 whereas Compton scattering goes roughly as Z A highZ material therefore favors the former two processes enabling the detection of the full energy of the gamma ray19 If the gamma rays are at higher energies 5 MeV pair production dominates Inorganic scintillators The scintillation process in inorganic materials is due to the electronic band structure found in crystals and is not molecular in nature as is the case with organic scintillators An incoming particle can excite an electron from the valence band to either the conduction band or the exciton band located just below the conduction band and separated from the valence band by an energy gap see picture This leaves an associated hole behind in the valence band Impurities create electronic levels in the forbidden gap The excitons are loosely bound electronhole pairs which wander through the crystal lattice until they are captured as a whole by impurity centers The latter then rapidly deexcite by emitting scintillation light fast component The activator impurities are typically chosen so that the emitted light is in the visible range or nearUV where photomultipliers are effective The holes associated with electrons in the conduction See Answer

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