RADIATION DETECTION AND MEASUREMENT

Lecture 04

Shahid Younas

Semi-Conductor Detectors- Basics

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An atom has protons an neutrons in the nucleus, with electrons orbiting

around the nucleus.

Semi-Conductor Detectors- Basics

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Courtesy by: Radiation Detection and Measurement; G.G. Knoll. 4 th Edition

Semi-Conductor Detectors- Basics

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Semi-Conductor Detectors- Basics

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Covalent BondsAtoms are joined by sharing electrons

e.g. H-H , Cl-Cl ,H-Cl

Semi-Conductor Detectors- Basics

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Metallic Bonds

Atom share their outer (valence) electrons

freely.

Electrons can move freely

Detached from its parent atom-delocalized.

Semi-Conductor Detectors- Basics

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You have studies Molecular, Ionic and Covenant Bonds. Do you know

about James Bond?

Semi-Conductor Detectors- Basics

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In crystalline materials,

electrons exist in energy

bands, separated by forbidden

gaps.

In metals least tightly bound

electrons exist in a partially

occupied band- conduction

band.

Semi-Conductor Detectors- Basics

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Do you know the difference between crystalline and semi conductor materials?

Semi-Conductor Detectors- Basics

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In insulator or semi-conductor the

valence electrons exist in a filled

valence band.

Semi-Conductor Detectors- Basics

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Covalent Bond

immobile

The next higher energy band-

conduction band, is empty of

electrons.

Semi-Conductor Detectors- Basics

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However, if an electron is placed

in conduction band, it is mobile,

as are the upper band electrons in

metals.

Semi-Conductor Detectors- Basics

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Do you know how much Toll-Tax needs to pay to move the electrons in

conduction band in semi-conductor and conductors?

Band gap Energy is 1-2 eV and 5 eV respectively.

Semi-Conductor Detectors- Basics

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1. Valence band electron.

migrates to conduction band.

2. Hole creation.

3. Mobile positive charge.

4. Hole-electron pair.

Semi-Conductor Detectors- Basics

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Semi-conductor can be then used as radiation detector.

Ionizing radiation, visible or ultraviolet light, or thermal energy can

donate 1 eV to raise the electrons in conduction band.

Semi-Conductor Detectors- Basics

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Semi-conductor can be then used as radiation detector.

Applied voltage between terminals on opposite of crystals.

Electric current flows.

Similar gas-filled detector.

Semi-Conductor Detectors- Basics

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Doping- tracer amount of impurities.

Impurity atoms fills sites in the crystal lattice that would

otherwise by occupied by atoms of the semiconductor material.

p-type and n-type materials.

semi-conductor diodes.

Semi-Conductor Detectors- Basics

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Unfortunately,

radiation induced current is “masked” by a larger current induced by

applied voltage.

Semi-Conductor Detectors- Basics

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Cadmium zinc telluride (CZT)

High Cost

Low Quantum Detection Efficiency

Cooling required

Semi-Conductor Detectors- Basics

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CZT is one of the examples of semi-conductor materials?

Do you know another semi-conductor material.

Semi-Conductor Detectors- Basics

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Have you thought of a Gamma Camera other than NaI(Tl)?

Semi-Conductor Detectors- Basics

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Today we shall perform Detection Efficiency of Dose Calibrators in

Injection Room.

Happy Birthday to my beloved Father!

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You are 73 Years now.