05 - Scintillation detectors
Jaroslav Adam
Czech Technical University in Prague
Version 1.0
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Scintillation detector principles
Ionizing radiation detected by scintillation light
Suitable scintillation material should follow some basic requirements
Inorganic crystals (NaI)
Organic liquids and plastic
Fluorescence = emission of visible radiation after excitation
Phosphorescence is emission with longer wavelength
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Organic scintillators
Fluorescence by transitions in a single molecule
π-electron structure
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Absorption and emission spectra of organic scintillator
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Scintillation efficiency
Fraction of energy of incident particle converted into visible light
Quenching at impurities
Transfer of excitation energy from molecule to molecule - binary scintillator
Tertiary organic mixture with waveshifter
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Pure organic crystals
Anthracene - oldest organic scintillator
Stilbene - fast response
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Liquid organic solutions
Organic scintillator in solvent (+ wavelength shifter)
Large active volume ∼ meters
Radiation resistant (no solid structure)
Radioactive material may be present in the solution
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Plastic scintillators
Polymerized organic scintillator in solvent
Arbitrary shape of final scintillator, large volume
Radiation damage depends on nature of radiation
May cause decrease of light output and/or decrease of light transparency
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Thin film scintillators
Very thin film of plastic scintillator, lower than range of weakly penetrating particles (heavy
ions)
Response as light yield per unit energy loss, depends on ion velocity and Z
Transmission detector for protons and alpha, fast timing
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Loaded organic scintillators
Direct detection of alpha and beta
Addition of high-Z material to allow for photoelectric conversions
Neutron detection with conversion elements
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Light output of organic scintillator
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Alpha-to-beta ratio
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Absolute scintillation efficiency
Normalization constant in relation between fluorescence energy and specific energy loss
Variability among different materials
Effect of radiation damage, surface crazing
Degradation by long-term exposure to light and oxygen
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Time response
Time to populate optical levels either exponential or Gaussian, followed by exponential decay
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Pulse shape discrimination in organic scintillators
Larger delayed constant for delayed fluorescence
Depends on specific energy loss, allows for particle identification
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Inorganic scintillators
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Emission spectrum of inorganic scintillators
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NaI(Tl)
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NaI(Tl) temperature dependence
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NaI(Tl) temperature dependence
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CsI(Tl) and CsI(Na)
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BGO
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Other slow (>200 ns) inorganic crystals
CdWO4 and CaWO4
ZnS(Ag)
CaF2 (Eu)
SrI2 (Eu)
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BaF2
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Other unactivated fast inorganics
CsI
Cerium halides
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Cerium activated fast inorganics
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Transparent ceramic scintillators
Nanocrystals in polycrystalline solid
Used for X-ray tomography
Allows for many combinations of materials and activators
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Glass scintillators
Silicate glass + Li + Ce activator
Neutron detection
Beta/gamma counting at severe environment
Imaging application
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Noble gas scintillators
High purity gas as scintillation material, Xe, He
Gas molecules excited by ionizing particle, UV scintillation light
Arbitrary size and shape
Linear response for specific energy loss measurement
Secondary scintillation in proportional region with external electric field
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Cryogenic liquid and solid scintillators
Liquid/solid Ar, Kr, Xe or He
High scintillation efficiency, emission in UV region
PM at cryogenic temperature
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Radiation damage in inorganic scintillators
Reduction of transparency
Interference with scintillation mechanism
Effects rate dependent
Annealing at room temperature
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Light collection and scintillator mounting
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Light pipes
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Strip light guide
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Fiber scintillators
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Ribbon array of fiber scintillators
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Glass capillaries in bundle
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Wavelength shifters
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Remote detection of X-rays
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