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

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Effect of Photon Energy on Attenuation Absorption characteristics will increase or decrease as the energy of the x- ray is increased or decreased. Since attenuation characteristics of materials are important in the development of contrast in a radiograph, an understanding of the relationship between material thickness, absorption properties, and photon energy is fundamental to producing a quality radiograph. A radiograph with higher contrast will provide greater probability of detection of a given discontinuity. An understanding of absorption is also necessary when designing x-ray and gamma ray shielding, cabinets, or exposure vaults. The applet below can be used to investigate the effect that photon energy has on the type of interaction that the photon is likely to have with a particle of the material (shown in gray). Various materials and material thicknesses may be selected and the x-ray energy can be set to produce a range from 1 to 199 KeV. Notice as various experiments are run with the applets that low energy radiation produces predominately photoelectric events and higher energy x- rays produce predominately Compton scattering events. Also notice that if the energy is too low, none of the radiation penetrates the material. Charlie Chong/ Fion Zhang
This second applet is similar to the one above except that the voltage (KVp) for a typical generic x-ray tube source can be selected. The applet displays the spectrum of photon energies (without any filtering) that the x-ray source produces at the selected voltage. Pressing the "Emit X-ray" button will show the interaction that will occur from one photon with an energy within the spectrum. Pressing the "Auto" button will show the interactions from a large number of photos with energies within the spectrum. 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
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
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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 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: Photoelectric (PE) absorption Photo
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
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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Charlie Chong/ Fion Zhang
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Manhattan Project Charlie Chong/ Fi
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WWII Charlie Chong/ Fion Zhang
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Ion Chamber Charger & Reader Radiac
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Quartz Fiber Pocket Dosimeter. Char
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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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