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

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This depletion region is the sensitive part of the detector and is analogous to the gas volume in a gas ionization detector. Charged particles, on entering the depletion region, produce electron hole pairs analogous to the ion pairs produced in gas ionization chambers. Because an electric field exists in this region, the charge produced by the ionizing particle is collected, producing a pulse of current. The size of the pulse is proportional to the energy expended by the particle. Charlie Chong/ Fion Zhang
Surface Barrier Detectors The operation of surface barrier and lithium drifted detectors is the same as for the p-n junction: a depletion region is produced, in which there exists an electric field. The means of producing the depletion region (as well as its dimension and location within the crystal) vary from one type of detector to another. The operation of a surface barrier detector (Fig. 21b) depends on the surface conditions of the silicon or germanium. At the surface of a piece of pure crystal, an electric field exists such that both holes and electrons are excluded from a thin region near the surface. For n type crystals, the field repels free electrons. If a metal is joined to the crystal, the free electrons are still repelled but a concentration of holes is produced directly under the surface. If a reverse bias is then applied, a depletion region is produced. Surface barrier detectors give better resolution for particle spectroscopy than p-n junctions but wider depletion regions are possible with the latter. (The wider the depletion region, the higher the energy of particles can be analyzed because a particle must expend all its energy in a depletion region.) 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
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FIGURE 2. Basic ionization chamber
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Photoelectric Absorption An atom co
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Compton Scatter Collision of a phot
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Pair Production Note pair productio
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Linear Energy Transfer [LET] LET is
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Simulation of various radiation ene
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Sources of Attenuation The attenuat
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Charlie Chong/ Fion Zhang http://ra
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The electron that is removed is the
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Photoelectric effect ABSORBED Charl
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Compton effect or Compton scatter i
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The reason at least 1.022 MeV of ph
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Pair Production Charlie Chong/ Fion
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Photoelectric (PE) absorption Photo
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This second applet is similar to th
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Photoelectric effect, or photoelect
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First principle mechanism of ioniza
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Photoelectron Spectroscopy Charlie
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Photoelectron Spectroscopy Charlie
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Thomson scattering (R), also known
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Ion current chambers have a respons
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FIGURE 4. Energy and directional re
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Ionization Chambers Charlie Chong/
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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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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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Page 233 and 234: PART 8. Film Badges One of the most
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Understanding Neutron Radiography Post Exam Reading VIII-Part 2a of 2A

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