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

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Electromagnetic Energy Interactions Photons interact with subatomic structures in one of the following three ways: •Photoelectric absorption •Compton Scatter •Pair production The particular type of interaction reflects probability statistics based on both the energy of the photon and the atomic number of the traversed atom. For most tissues of the body, average atomic number does not vary greatly – though cortical bone has the highest effective atomic number. Charlie Chong/ Fion Zhang https://www.med-ed.virginia.edu/courses/rad/radbiol/01physics/phys-03-02.html
Photoelectric Absorption An atom completely absorbs a photon, which then disappears; this excess energy provided to the atom ultimately results in ejection of an orbital electron. The ejected electron is known as a photo electron. Electrons have binding energies of orbit, with outer shells having less energy than those closer to the positive nucleus. When the initial orbital vacated is not that of an outer valance electron, the atom remains in a high-energy state until an outer orbital electron shifts to fill its incomplete inner shell. This shift is accompanied by emission of a characteristic X-ray. Photoelectric Absorption is an important interaction for low energy photons (
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: FIGURE 2. Basic ionization chamber
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
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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
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Page 77 and 78: Compton scattering (C) (incoherent
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Output Current Measurements The ion
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Vibrating Reed Electrometers An alt
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Vibrating Reed Electrometers Cary V
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The weak current generated in the c
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Older electrometers Gold-leaf elect
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Charlie Chong/ Fion Zhang Volta Ele
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Gold-leaf electroscope Charlie Chon
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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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