scintillators hoda bagheri spring 2010. light emission scintillators scintillation mechanism ...

ScintillatorsScintillators

HodaHoda BagheriBagheri

Spring 2010Spring 2010

Light emissionLight emission ScintillatorsScintillators Scintillation mechanismScintillation mechanism PhotomultiplayerPhotomultiplayer

light emissionlight emission

(1) thermal radiation----black-body (1) thermal radiation----black-body radiation, etc.radiation, etc. (2) braking radiation(2) braking radiation (3) Cherenkov radiation(3) Cherenkov radiation (4) luminescence---usually in the (4) luminescence---usually in the visible, UV, IR range visible, UV, IR range

Luminescence excited by Luminescence excited by different external energiesdifferent external energies::

photo-luminescene---by UV photons, etc.photo-luminescene---by UV photons, etc. radio---by radiation like X-, radio---by radiation like X-, ,rays,rays, etc. , etc. cathode- ---by electron beam,cathode- ---by electron beam, electro----by electric field, (examples: LED)electro----by electric field, (examples: LED)

Scintillation ~ Scintillation ~ Fluoarescence due to Fluoarescence due to

radiationradiation

Scintillators:Scintillators:

Inorganic: Inorganic: crystals,crystals, ceramics, ceramics, glasses, glasses, noble liquid, noble liquid, noble gassesnoble gasses

Organic: crystalsOrganic: crystals, liquid, plastic, liquid, plastic

ScintillationScintillation mechanism mechanism

Four types of luminescence in inorganic scintillators

(1 )Exciton luminescence :BGO… ,

(2 )Dopant luminescence :GSO:Ce… ,

(3 )Charge-transfer luminescence

(4 )CVL (Core-valence luminescence ,

Cross luminescence)

ScintillationScintillation mechanism mechanism

Scintillation mechanism in organic Scintillation mechanism in organic scintillatorsscintillators

Radiative transition of electrons

Main characteristicsMain characteristics

1. Quenching1. Quenching

(1) Thermal quenching

(2 )impurity quenching

(3 )concentration quenchin

Main characteristicsMain characteristics

2. Decay2. Decay

(2 )Afterglow due to metasatble states or traps

(1 )Natural afterglow-

I(t) = I(0) exp(-t/) = (Pnr + Pr)-1

Main characteristicsMain characteristics

3. Particle discrimination3. Particle discrimination

Possible for some inorganicand most of organic scintillators.

Particle discriminationParticle discrimination

Comparison betwee inorganic and organic scintillators

Photomultiplier tubePhotomultiplier tube

Gain ~ 106 - 107

Gain ~ 106 - 107

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