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SOLID STATE DETECTOR

MAMITA SAKHAKARMIB.Sc.MIT4th BATCH 1ST YEARChitwan Medical College

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DETECTORSAn instrument responsible for detection of ionizing radiations by interacting with matter or to measure radiation or to do both.

Types Gas filled detectorSolid state detector

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SOLID STATE DETECTORThis consists of the solid materials with fluorescence, phosphorescence and semiconducting properties.

Types Scintillation Detector Thermo luminescent dosimeter Semiconductor Detector

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Scintillation detectors: Detectors based on scintillation (light

emission)

Working Principle

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Types Inorganic crystals Organic crystals

Inorganic crystals Generally, high atomic number and high density

materials NaI, CsI, Lithium glasses, ZnS

Commonly used for gamma-ray detection High light yield (60,000/ Mev) Can’t be used in liquid form. Low decay time about 1 microsecond

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INORGANIC SCINTILLATORS

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Organic crystals low atomic numbers, relatively low density. Low light yield (1000photons/ Mev)-power signal Can be used in both liquid and solid form. Economic Fast decay time about 10 nanosecond Commonly used for Beta particles detectionE.g. trans-stilbene, Anthracene, Naphthalene etc.

Generally, in our department inorganic crystals are used because of their high at. no. n high densities that make them good x-ray n gamma ray detector.

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ORGANIC SCINTILLATORS COME IN MANY FORMS

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THERMO LUMINESCENT DOSIMETER• TLD is excellent personnel and environmental

dosimeter.• It is based on Thermoluminescence.

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Measurement of Thermoluminescence

“Captures” radiation dose information in a crystal matrix.

Releases light when heated, light intensity proportional to radiation dose absorbed.

Information destroyed when processed.

Should be annealed before reused.

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TYPES OF TLD MATERIALCommonly used LiF:Mg,Ti, LiF:Mg,Cu,P and Li2B4O7:Mn, because of their tissue equivalence.

Most widely used is LiF. Atomic no. is 8.2 that is nearly tissue equivalent (7.4 for soft tissue) LiF is relatively sensitive and can measure as low as 5 mRad with modest

accuracy.

CaF2 has higher effective atomic no. (z= 16.3) TLDs are available in various forms (e.g. powder, chips, rods and

ribbons). Can be expensive (reusable chips)

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Glow curve : graph obtained by plotting phosphor temperature (ºC) against intensity of emitted light.

Phosphor temperature (C)

Emitt

ed L

ight

In

tens

ity

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Practical consideration :

Must be calibrated before use. Since the response of the TLD material is

affected by their previous radiation history and thermal history, the material must be annealed to removed residual effect.

Should be worn at chest position. Changed in every 3 months. Should be stored away from light, radiation

and dust when it is not used. Should not be used beside concern

personnel.

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SEMICONDUCTOR DETECTOR

Detector of choice of very high resolution energy measurement

Response that varies linearly with the energy deposited in the detector and doesn't depend upon the type of radiation that deposits the energy

Negligible absorption of energy Small detector size

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Act as a solid state ionization chamber. Operation depends on having either an

excess of electrons or an excess of holes

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Semiconductor Detectors

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Common materials of choice Silicon and Geranium

Generally, used for the detection of alpha and beta particles.

Light radiation can be detected in semiconductors through release of charges across the band gap

Higher energy radiation can be expected to do so at much higher efficiencies.

A metal-oxide semiconductor field effect transistor (MOSFET) is a miniature silicon transistor.

Use as vivo dosimeter in rectum and urinary bladder

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Thank

you!