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

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

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

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  1. Understanding Neutron R adiography R eading VIII Part 2(a)of 2 16thAugust 2016 Post Exam Reading Charlie Chong/ Fion Zhang

  2. Spallation Source Charlie Chong/ Fion Zhang

  3. Spallation Source Charlie Chong/ Fion Zhang

  4. Spallation Source http://www.gizmodo.com.au/2014/01/27-amazing-images-from-the-depths-of-scientific-labs/ Charlie Chong/ Fion Zhang

  5. Spallation Source http://www.gizmodo.com.au/2014/01/27-amazing-images-from-the-depths-of-scientific-labs/ Charlie Chong/ Fion Zhang

  6. The Magical Book of Neutron Radiography Charlie Chong/ Fion Zhang

  7. 数字签名 者：Fion Zhang DN：cn=Fion Zhang, o=Technical, ou=Academic, email=fion_zhang @qq.com, c=CN 日期：2016.08.19 23:29:54 +08'00' Charlie Chong/ Fion Zhang

  8. ASNT Certification Guide NDT Level III / PdM Level III NR - Neutron Radiographic Testing Length: 4 hours Questions: 135 1. Principles/Theory • Nature of penetrating radiation • Interaction between penetrating radiation and matter • Neutron radiography imaging • Radiometry 2. Equipment/Materials • Sources of neutrons • Radiation detectors • Non-imaging devices Charlie Chong/ Fion Zhang

  9. 3. Techniques/Calibrations • Electron emission radiography • Blocking and filtering • Micro-radiography • Multifilm technique • Laminography (tomography) • Enlargement and projection • Control of diffraction effects • Stereoradiography • Panoramic exposures • Triangulation methods • Gaging • Autoradiography • Real time imaging • Flash Radiography • Image analysis techniques • In-motion radiography • Fluoroscopy Charlie Chong/ Fion Zhang

  10. 4. Interpretation/Evaluation • Image-object relationships • Material considerations • Codes, standards, and specifications 5. Procedures • Imaging considerations • Film processing • Viewing of radiographs • Judging radiographic quality 6. Safety and Health • Exposure hazards • Methods of controlling radiation exposure • Operation and emergency procedures Reference Catalog Number NDT Handbook, Third Edition: Volume 4, Radiographic Testing 144 ASM Handbook Vol. 17, NDE and QC 105 Charlie Chong/ Fion Zhang

  11. Fion Zhang at Copenhagen Harbor 16thAugust 2016 Charlie Chong/ Fion Zhang

  12. SME- Subject Matter Expert http://cn.bing.com/videos/search?q=Walter+Lewin&FORM=HDRSC3 https://www.youtube.com/channel/UCiEHVhv0SBMpP75JbzJShqw Charlie Chong/ Fion Zhang

  13. Gamma- Radiography TABLE 1. Characteristics of three isotope sources commonly used for radiography. Source T½ Energy HVL Pb HVL Fe Specific Activity Dose rate* Co60 5.3 year 1.17, 1.33 MeV 12.5mm 22.1mm 50 Cig-1 1.37011 Cs137 30 years 0.66 MeV 6.4mm 17.2mm 25 Cig-1 0.38184 Ir192 75 days 0.14 ~ 1.2 MeV (Aver. 0.34 MeV) 4.8mm ? 350 Cig-1 0.59163 Th232 0.068376 Dose rate* Rem/hrat one meter per curie Charlie Chong/ Fion Zhang

  14. 八千里路云和月 Charlie Chong/ Fion Zhang

  15. Charlie Chong/ Fion Zhang

  16. 闭门练功 Charlie Chong/ Fion Zhang

  17. Charlie Chong/ Fion Zhang http://greekhouseoffonts.com/

  18. Charlie Chong/ Fion Zhang

  19. W hole Chapter 5 R adiation Measurement Charlie Chong/ Fion Zhang

  20. PAR T 1. Principles of R adiation Measurement Emissions from radioactive nuclei and radiation from that portion of the electromagnetic spectrum beyond the ultraviolet energies can cause the ionization of atoms and molecules. Ionizing radiation occurs as three forms: (1) charged particles such as alpha particles, beta particles and protons, (2) uncharged particles such as neutrons and (3) electromagnetic radiation in the form of X-rays and gamma rays. Charlie Chong/ Fion Zhang

  21. R adiation Detection Systems Some forms of radiation, such as light and heat, can be detected by human sense organs; ionizing radiation, however, can be detected only by the after effect of itsionizing properties. If ionizing radiation does not interact with matter, its detection and measurement is impossible. For this reason, the detection process uses substances that respond to radiation, as part of a system for measuring the extent of that response. The ionization process isused by a large class of detection systems, including: ■ ion chambers, ■ proportional chambers, ■ geiger-müller counters and ■ semiconductor devices (Table 1). ■ Some systems depend on the excitation and molecular dissociation (分子离解) that occur with ionization. These processes are useful in (1) scintillation counters and (2) chemical dosimeters. Although other types of detection systems exist, they are not generally used in radiation survey instruments. Charlie Chong/ Fion Zhang

  22. TABLE 1. Effect of detected and measured ionization. Charlie Chong/ Fion Zhang

  23. PAR T 2. Ion Chambers and Proportional Counters Principles of Ionization The mechanism most widely used in radiation survey applications is the ionization principle: charged particles producing ion pairs by direct interaction. These charged particles may (1) collide with electrons and remove them from their atoms or (2) transfer energy to an electron by the interaction of their electric fields (Fig. 1). If the energy transfer is not sufficient to completely remove an electron, the atom is left in a disturbed or excited state. Gamma and X-ray photons interact with matter mainly by: ■ photoelectric absorption, ■ compton scattering and ■ pair production, each of which produces electrons and ions that may be collected and measured. Charlie Chong/ Fion Zhang

  24. The average energy expended in the creation of an ion pair, in air and most gases, is about 34 eV) . The number of ion pairs produced per unit of path length is called specific ionization. Specific ionization is affected by the energy of the particle or photon by its change and by the nature of the ionized substance. Charlie Chong/ Fion Zhang

  25. FIGURE 1. Ion pair (showing ejected electron and vacancy in electron orbit of atom). pair 34 eV for Air Charlie Chong/ Fion Zhang

  26. Ionization Chambers In an ionization chamber, an electric field is applied across a volume of gas, between two electrodes. Often the chamber’s geometry is cylindrical, a cylindrical cathode enclosing the gas and an axial, insulated rod anode (Fig. 2). Charged particles, photons or both pass through the chamber and ionize the enclosed gas. When an electric field is applied to the gas, ions drift along the electrical lines of force to produce an ionization current. Under normal conditions, electrons drift at speeds of about 104 m·s–1(22 000 mi·h–1). The drift velocity of positive ions is many orders of magnitude less. When the electric field is increased slightly from zero and a detector is placed in the constant radiation field the collected ions still will be few in number because many recombine. As the voltage is further increased, recombination yields to ionization, where all ions are collected (Fig. 3). Charlie Chong/ Fion Zhang

  27. FIGURE 2. Basic ionization chamber with high value resistance R and voltage V. Charlie Chong/ Fion Zhang

  28. 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. https://www.med-ed.virginia.edu/courses/rad/radbiol/01physics/phys-03-02.html Charlie Chong/ Fion Zhang

  29. 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 (<100 KeV) (<0.1Mev) . Note: <0.34MeV (Exam Q) https://www.med-ed.virginia.edu/courses/rad/radbiol/01physics/phys-03-03.html Charlie Chong/ Fion Zhang

  30. True or False? The "photo electron" and free radical can interact with other molecules -- ultimately leading to ionizations and bond breakage, which are the biologically-important molecular manifestations of radiation damage. https://www.med-ed.virginia.edu/courses/rad/radbiol/01physics/phys-03-03.html Charlie Chong/ Fion Zhang

  31. Compton Scatter Collision of a photon with an electron increases the kinetic energy of the electron. Thus set in motion, the electron is known as a recoil electron. The incident photon’s energy is not necessarily depleted, but it will diverge from its path and have lower energy -- i.e., it has a longer wavelength after collision. In diagnostic radiology, such scattered photons may lower contrast and thus degrade quality of the radiographic image. Important interaction for intermediate-energy photons (100 KeV to 10 MeV) Note: 0.34 ~ 1.2 MeV (Exam Q) https://www.med-ed.virginia.edu/courses/rad/radbiol/01physics/phys-03-03.html Charlie Chong/ Fion Zhang

  32. Compton Scatter https://www.med-ed.virginia.edu/courses/rad/radbiol/01physics/phys-03-03.html Charlie Chong/ Fion Zhang

  33. Pair Production Note pair production requires relatively high photon energies that are generally not produced in diagnostic imaging. Photons with quantum energy in excess of 1.02 MeV (usually >10 MeV) may interact with matter to produce a negative electron and its anti-particle (positron). The value of 1.02 MeV equals the combination rest mass energy of an electron and a positron. https://www.med-ed.virginia.edu/courses/rad/radbiol/01physics/phys-03-03.html Charlie Chong/ Fion Zhang

  34. Pair Production 0.51MeV 0.51MeV https://www.med-ed.virginia.edu/courses/rad/radbiol/01physics/phys-03-03.html Charlie Chong/ Fion Zhang

  35. Linear Energy Transfer [LET] LET is the amount of energy transferred to the local environment in the form of ionizations and excitations. Thus, LET indicates the potential for biologically important damage from radiation. Linear Energy Transfer can be thought of in two ways: • an average energy for a given path length traveled or • an average path length for a given deposited energy. The standard unit of measure is keV/um. https://www.med-ed.virginia.edu/courses/rad/radbiol/01physics/phys-03-03.html Charlie Chong/ Fion Zhang

  36. Ionization tracts. When particulate or electromagnetic energy penetrates a cell, one or more ionizations will likely take place. While the precise site of interaction is somewhat random, ionizations will distribute along distinct paths. The density of ionizations along a given path relates inversely to kinetic energy of the particle or photon. Thus a decelerating particle produces the greatest number of ionizations just before coming to rest. Comparing particles or photons, it follows also that LET for a gamma ray may be smaller than LET for an x-ray. https://www.med-ed.virginia.edu/courses/rad/radbiol/01physics/phys-03-03.html Charlie Chong/ Fion Zhang

  37. Simulation of various radiation energies passing through a medium – each hatch mark represents an ionization. The heavy ion is a very high-LET particle; the delta ray represents secondary electrons with sufficient energy to make a separate ionization tract. The 5 keV electron is the typical energy of a secondary electron produced by X-ray photons used in diagnostic imaging. Note that absorption (and attenuation) of a photon beam is related to the atomic number of the impinged mass and inversely related to the energy of the incident photon beam. The medium shown is approximately 200 nm in width – a DNA double helix width is about 2 nm. (Developed after Cox J.D. and Ang K.K., eds. Radiation Oncology Rationale, Technique, Results. 8th edition. St Louis, MO: Mosby, 2003. p44.) https://www.med-ed.virginia.edu/courses/rad/radbiol/01physics/phys-03-03.html Charlie Chong/ Fion Zhang

  38. Simulation of various radiation energies passing through a medium https://www.med-ed.virginia.edu/courses/rad/radbiol/01physics/phys-03-03.html Charlie Chong/ Fion Zhang

  39. Sources of Attenuation The attenuation that results due to the interaction between penetrating radiation and matter is not a simple process. A single interaction event between a primary x-ray photon and a particle of matter does not usually result in the photon changing to some other form of energy and effectively disappearing. Several interaction events are usually involved and the total attenuation is the sum of the attenuation due to different types of interactions. These interactions include the photoelectric effect, scattering, and pair production. The figure below shows an approximation of the total absorption coefficient, (µ), in red, for iron plotted as a function of radiation energy. The four radiation-matter interactions that contribute to the total absorption are shown in black. The four types of interactions are: photoelectric (PE), Compton scattering (C), pair production (PP), and Thomson or Rayleigh scattering (R). Since most industrial radiography is done in the 0.1 to 1.5 MeV range, it can be seen from the plot that photoelectric and Compton scattering account for the majority of attenuation encountered. https://www.nde-ed.org/EducationResources/CommunityCollege/Radiography/Physics/attenuation.htm Charlie Chong/ Fion Zhang

  40. Total Absorption Coefficient, (µ), photoelectric (PE), Compton scattering (C), pair production (PP), and Thomson or Rayleigh scattering (R). µ Charlie Chong/ Fion Zhang

  41. Charlie Chong/ Fion Zhang

  42. Coherent scattering (also known as unmodified, classical or elastic scattering) is one of three forms of photon interaction which occurs when the energy of the X-ray or gamma photon is small in relation to the ionisation energy of the atom. It therefore occurs with low energy radiation. Upon interacting with the attenuating medium, the photon does not have enough energy to liberate the electron from its bound state (i.e. the photon energy is well below the binding energy of the electron) so no energy transfer occurs. The only change is a change of direction (scatter) of the photon, hence 'unmodified' scatter. Coherent scattering is not a major interaction process encountered in radiography at the energies normally used. Coherent scattering varies with the atomic number of absorber (Z) and incident photon energy (E) by Z2/ E. http://radiopaedia.org/articles/coherent-scattering Charlie Chong/ Fion Zhang

  43. http://radiopaedia.org/articles/coherent-scattering Charlie Chong/ Fion Zhang

  44. 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) http://radiopaedia.org/articles/photoelectric-effect Charlie Chong/ Fion Zhang

  45. 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. http://radiopaedia.org/articles/photoelectric-effect Charlie Chong/ Fion Zhang

  46. The incident photon is completely absorbed in the process. Charlie Chong/ Fion Zhang

  47. Photoelectric effect ABSOR BED Charlie Chong/ Fion Zhang

  48. Completely Heroes Charlie Chong/ Fion Zhang

  49. Compton effect or Compton scatter is one of three principle forms of photon interaction. It is the main cause of scattered radiation in a material. It occurs due to the interaction of the X-ray or gamma photon with the outermost (and hence loosely bound) valence electron at the atomic level. The resultant incident photon gets scattered (changes direction) as well as ejects the electron (recoil electron), which further ionizes other atoms. Therefore the Compton effect is a partial absorption process and as the original photon has lost energy, this is known as Compton shift (the shift being a shift of wavelength/frequency). Probability of Compton effect:  directly proportional to • number of outer shell electrons, i.e. the electron density • physical density of material  inversely proportional to • photon energy  does not depend on • atomic number (unlike photoelectric effect and pair production) http://radiopaedia.org/articles/compton-effect Charlie Chong/ Fion Zhang

  50. History and etymology Named after Professor Arthur Holly Compton (1892- 1962), US physicist, who was awarded the Nobel Prize in Physics in 1927 for his discovery of Compton effect. Charlie Chong/ Fion Zhang

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