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

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Pair production (PP) can occur when the x-ray photon energy is greater than 1.02 MeV, but really only becomes significant at energies around 10 MeV. Pair production occurs when an electron and positron are created with the annihilation of the x-ray photon. Positrons are very short lived and disappear (positron annihilation) with the formation of two photons of 0.51 MeV energy. Pair production is of particular importance when high-energy photons pass through materials of a high atomic number. (single photon for single pair production or single high energy photon for multiple pair production?) Charlie Chong/ Fion Zhang https://www.nde-ed.org/EducationResources/CommunityCollege/Radiography/Physics/attenuation.htm
Output Current Measurements The ionization current collected in the ion chamber flows through an external circuit for measurement. Although in principle an ammeter could be placed in the external circuit to read the ion current, in practice the ammeter is not placed there, for the current is very small. A 440 cm 3 (27 in. 3 ) ion chamber typically produces about 4 × 10 –15 A·μSv –1 (4 × 10 –14 A·mR –1 ) at standard temperature and pressure. A high valued load resistor (on the order of 10 10 Ω) is placed in the circuit and the voltage drop across the resistor is measured with a sensitive electrometer. A metal oxide silicon field effect transistor (MOSFET) is used in some electrometers. The metal oxide silicon field effect transistor produces an input impedance on the order of 10 15 Ω to amplify the collected current (Fig. 5). Charlie Chong/ Fion Zhang
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Understanding Neutron Radiography R
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Spallation Source Charlie Chong/ Fi
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Spallation Source Charlie Chong/ Fi
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Charlie Chong/ Fion Zhang
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3. Techniques/Calibrations • Bloc
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Charlie Chong/ Fion Zhang Fion Zhan
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Gamma- Radiography TABLE 1. Charact
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Charlie Chong/ Fion Zhang http://gr
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Whole Chapter 5 Radiation Measureme
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Radiation Detection Systems Some fo
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PART 2. Ion Chambers and Proportion
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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 45 and 46: The electron that is removed is the
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: Compton scattering (C) (incoherent
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
Page 89 and 90: Charlie Chong/ Fion Zhang Volta Ele
Page 91 and 92: Gold-leaf electroscope Charlie Chon
Page 93 and 94: Vibrating reed electrometers Vibrat
Page 95 and 96: FIGURE 7. Examples of ionization ch
Page 97 and 98: FIGURE 8. Cross section of quartz f
Page 99 and 100: Quartz Fiber Pocket Dosimeter. Char
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Page 113 and 114: WWII Charlie Chong/ Fion Zhang
Page 115 and 116: Ion Chamber Charger & Reader Radiac
Page 119 and 120: Pocket dosimeters tended to be slig
Page 121 and 122: Quartz Fiber Pocket Dosimeter. CDV-
Page 125 and 126: Ion Chamber Charger & Reader Charli
Page 127 and 128: 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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