This document discusses semi-conductor detectors and their use in radiation detection. It describes the basic structure of atoms and different types of bonds between atoms. It explains that in crystalline materials like semiconductors, electrons exist in energy bands separated by gaps. In semiconductors and insulators, the valence band is full while the conduction band is empty, allowing electrons to move if given enough energy to cross the band gap. Semiconductors can be "doped" with impurities to create p-type or n-type materials and function as radiation detectors by generating electron-hole pairs when ionizing radiation transfers electrons to the conduction band.

1. RADIATION DETECTION AND MEASUREMENT
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Shahid Younas

2. Semi-Conductor Detectors- Basics
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An atom has protons an neutrons in the
nucleus, with electrons orbiting
around the nucleus.

3. Semi-Conductor Detectors- Basics
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Courtesy by: Radiation Detection and Measurement; G.G. Knoll. 4th Edition

4. Semi-Conductor Detectors- Basics
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5. Semi-Conductor Detectors- Basics
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Covalent Bonds
Atoms are joined by sharing electrons
e.g. H-H , Cl-Cl ,H-Cl

6. 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.

7. Semi-Conductor Detectors- Basics
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You have studies Molecular, Ionic and Covenant Bonds. Do you know
about James Bond?

8. 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.

9. Semi-Conductor Detectors- Basics
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Do you know the difference between crystalline and semi
conductor materials?

10. Semi-Conductor Detectors- Basics
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In insulator or semi-conductor the
valence electrons exist in a filled
valence band.

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 Covalent Bond
 immobile
 The next higher energy band-
conduction band, is empty of
electrons.

12. 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.

13. 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.

14. 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.

15. 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.

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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.

17. 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.

18. Semi-Conductor Detectors- Basics
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Unfortunately,
radiation induced current is “masked” by a larger current induced by
applied voltage.

19. Semi-Conductor Detectors- Basics
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 Cadmium zinc telluride (CZT)
 High Cost
 Low Quantum Detection Efficiency
 Cooling required

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CZT is one of the examples of semi-conductor materials?
Do you know another semi-conductor material.

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

22. Semi-Conductor Detectors- Basics
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Today we shall perform Detection Efficiency of Dose Calibrators in
Injection Room.

23. Happy Birthday to my beloved Father!
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You are 73 Years now.