Understanding Neutron Radiography Post Exam Reading VIII-Part 2a of 2A

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Photoelectric effect, or photoelectric absorption (PEA) is a form of interaction of X-ray or gamma photon with the matter. A low energy photon interacts with the electron in the atom and removes it from its shell. The probability of this effect is maximum when: • the energy of the incident photon is equal to or just greater than the binding energy of the electron in its shell ('absorption edge') and • the electron is tightly bound (as in K shell) Charlie Chong/ Fion Zhang http://radiopaedia.org/articles/photoelectric-effect
The electron that is removed is then called a photoelectron. The incident photon is completely absorbed in the process. Hence it forms one of the reason for attenuation of X-ray beam as it passes through the matter. PEA is related to the atomic number of the attenuating medium (Z), the energy of the incident photon (E) and the physical density of the attenuating medium (p) by: Z³ p / E³. Therefore, if Z doubles, PEA will increase by a factor of 8 (because 2³ is 8) and if E doubles, PEA will reduce by 8. As small changes in Z can have quite profound changes in PEA this has practical implications in the field of radiation protection and is why materials with a high Z such as lead (Z = 82) are useful shielding materials. Charlie Chong/ Fion Zhang http://radiopaedia.org/articles/photoelectric-effect
Page 1 and 2: Understanding Neutron Radiography R
Page 3 and 4: Spallation Source Charlie Chong/ Fi
Page 5 and 6: Spallation Source Charlie Chong/ Fi
Page 7 and 8: Charlie Chong/ Fion Zhang
Page 9 and 10: 3. Techniques/Calibrations • Bloc
Page 11 and 12: Charlie Chong/ Fion Zhang Fion Zhan
Page 13 and 14: Gamma- Radiography TABLE 1. Charact
Page 17 and 18: Charlie Chong/ Fion Zhang http://gr
Page 19 and 20: Whole Chapter 5 Radiation Measureme
Page 21 and 22: Radiation Detection Systems Some fo
Page 23 and 24: PART 2. Ion Chambers and Proportion
Page 25 and 26: FIGURE 1. Ion pair (showing ejected
Page 27 and 28: FIGURE 2. Basic ionization chamber
Page 29 and 30: Photoelectric Absorption An atom co
Page 31 and 32: Compton Scatter Collision of a phot
Page 33 and 34: Pair Production Note pair productio
Page 35 and 36: Linear Energy Transfer [LET] LET is
Page 37 and 38: Simulation of various radiation ene
Page 39 and 40: Sources of Attenuation The attenuat
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Page 47 and 48: Photoelectric effect ABSORBED Charl
Page 49 and 50: Compton effect or Compton scatter i
Page 53 and 54: The reason at least 1.022 MeV of ph
Page 55 and 56: Pair Production Charlie Chong/ Fion
Page 57 and 58: Photoelectric (PE) absorption Photo
Page 59 and 60: This second applet is similar to th
Page 61 and 62: Photoelectric effect, or photoelect
Page 63 and 64: First principle mechanism of ioniza
Page 65 and 66: Photoelectron Spectroscopy Charlie
Page 67 and 68: Photoelectron Spectroscopy Charlie
Page 69 and 70: Thomson scattering (R), also known
Page 71 and 72: Ion current chambers have a respons
Page 73 and 74: FIGURE 4. Energy and directional re
Page 75 and 76: Ionization Chambers Charlie Chong/
Page 77 and 78: Compton scattering (C) (incoherent
Page 79 and 80: Output Current Measurements The ion
Page 81 and 82: Vibrating Reed Electrometers An alt
Page 83 and 84: Vibrating Reed Electrometers Cary V
Page 85 and 86: The weak current generated in the c
Page 87 and 88: Older electrometers Gold-leaf elect
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Page 91 and 92: Gold-leaf electroscope Charlie Chon
Page 93 and 94: Vibrating reed electrometers Vibrat
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FIGURE 7. Examples of ionization ch
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FIGURE 8. Cross section of quartz f
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Quartz Fiber Pocket Dosimeter. Char
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Manhattan Project Charlie Chong/ Fi
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Charlie Chong/ Fion Zhang
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WWII Charlie Chong/ Fion Zhang
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Ion Chamber Charger & Reader Radiac
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Pocket dosimeters tended to be slig
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Quartz Fiber Pocket Dosimeter. CDV-
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Ion Chamber Charger & Reader Charli
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WWII Heroes Charlie Chong/ Fion Zha
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FIGURE 8. Cross section of quartz f
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FIGURE 10. Energy dependence of res
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Proportional Counters If the electr
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Townsend Discharges (Avalanches) Th
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General description of the phenomen
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The avalanche mechanism is shown in
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Visualization of Proportional Count
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Multiple Gas Amplification due to m
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PART 3. Geiger-Müller Counters Ope
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Visualization of Geiger Muller Gas
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Properties Extension of the gas ava
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Correct counting rate R can be calc
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FIGURE 11. Resolving time, dead tim
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FIGURE 12. Processing of detector i
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Quenching As positive ions are coll
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FIGURE 13. Assortment of geiger-mü
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Geiger Muller Charlie Chong/ Fion Z
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Design Variations Geiger-müller co
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FIGURE 14. Dose rate ratio versus e
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TABLE 1. Characteristics of three i
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Mini Geiger Muller Alarm Meter Char
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Mini Geiger Muller Alarm Meter Char
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FIGURE 15. Typical energy response
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(b) radiation incident on side vers
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(d) radiation incident normal to lo
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TABLE 3. Common scintillators. Char
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FIGURE 16. Energy diagram of scinti
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Desirable Scintillator Characterist
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Electron multiplication, or gain, i
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PMT Charlie Chong/ Fion Zhang
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PMT Charlie Chong/ Fion Zhang
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System Electronics Once the output
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PART 5. Luminescent Dosimetry Therm
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Thermoluminescence Charlie Chong/ F
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Disadvantages include the loss of i
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Thermoluminescent Dosimetric Readou
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FIGURE 20. Typical glow curve. Inte
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TDL Charlie Chong/ Fion Zhang http:
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TDL Charlie Chong/ Fion Zhang http:
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PART 6. Neutron Detection Character
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TABLE 4. Neutron classification. Cl
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Scintillation Scintillators contain
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TABLE 6. Properties of Some Thermal
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Detector The diffused p-n junction
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Surface Barrier Detectors The opera
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TABLE 5. Radiation detector types.
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FIGURE 21. Cross sections: (a) diff
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PART 8. Film Badges One of the most
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The absorption of a single photon o
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Compounds that can be used as photo
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Understanding Neutron Radiography Post Exam Reading VIII-Part 2a of 2A

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