Understanding Neutron Radiography Reading I-NDT-HBook-NRT-Rev01A

1. Understanding Neutron R adiography R eading I– NDT-H Book-NR T My ASNT Level III, Pre-Exam Preparatory Self Study Notes 21 June 2015 Second Reading 29 July 2016 Charlie Chong/ Fion Zhang

2. NRT Source Charlie Chong/ Fion Zhang

3. Neutron Source Charlie Chong/ Fion Zhang

4. Neutron Source- Linac Charlie Chong/ Fion Zhang

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

6. 数字签名 者：Fion Zhang DN：cn=Fion Zhang, o=Technical, ou=Academic, email=fion_zhan g@qq.com, c=CN 日期：2016.07.31 00:48:56 +08'00' Charlie Chong/ Fion Zhang

7. 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

8. 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

9. 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

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17. R eading I SECTION 12-Neutron R adiography Charlie Chong/ Fion Zhang

18. PART 0 INTRODUCTION Neutron radiography is a valuable nondestructive testing technique which ideally complements conventional radiography. The first publications covering neutron radiography found it convenient to compare a neutron radiograph, side-by-side, with an X-ray image, to point out the benefits of the neutron image. This sometimes gave the impression that the two techniques were competitive; happily, this has turned out not to be the case. Neutron radiography is now a widely accepted, specialized testing technique. Sometimes an object can be most thoroughly analyzed radiographically with both neutrons and X (or gamma) rays. This Section of the NDT Handbook is a useful reference to practicing neutron radiographers and can serve as an introduction for students or conventional radiographers as well. Charlie Chong/ Fion Zhang

19. The text includes helpful discussions on: 1. neutron sources; 2. moderation; 3. collimation; 4. techniques for neutron radiography; 5. neutron imaging methods; and 6. reference material concerning regulatory control, 7. neutron radiography standards and cross sections. Charlie Chong/ Fion Zhang

20. A discussion of applications is also included, with some well- llustrated examples. All of the authors for this Section deserve the gratitude. of the technical community, the Handbook Editor and the Handbook Coordinator. Special thanks go to Harry Berger, Industrial Quality, Inc., for his service as primary author and contact with the publications staff. The authors in turn extend their thanks to John P. Barton (N-Ray Engineering) for his helpful review of the chapter, to Roger A. Morris (Los Alamos National Laboratory) for permission to use the table of thermal neutron cross sections and attenuation coefficients, and to the American Society for Testing and Materials for permission to reprint the table of thermal neutron cross sections and attenuation coefficients (Table 9), and the Figure on halfvalue layers (Fig. 10). Charlie Chong/ Fion Zhang

21. PAR T 1 PR INCIPLES OF NEUTR ON R ADIOGR APH Y Charlie Chong/ Fion Zhang

22. 1.1 Development Radiography with thermal neutrons can be traced to the mid-1930s, shortly after the discovery of the neutron. Research work in this field has carried through to the present time, with a significant increase in developmental activity since 1960. Commercial interest in thermal neutron radiography began in the mid-1960s. 1.2 Principles Neutron radiography extends the ability to image the internal structure of a specimen, beyond what can be accomplished with photon (X and gamma) radiation. Similarities, as well as obvious differences, exist when neutron radiography is compared to photon radiographic techniques. Similarities include the ability to produce a visual record of changes in density, thickness and composition of a specimen. Indeed, the neutron radiograph can look very much like a photon radiograph. Charlie Chong/ Fion Zhang

23. Advantages lt is the differences between the techniques which provide the advantages of neutron radiographyover photon radiography. The major difference is the way in which neutrons are removed from the inspection beam by the specimen. Neutrons interact only with the nuclei of the atoms in the specimen; the neutrons may be scattered or absorbed by the atomic nuclei. Because the neutron interactions involve nuclei rather than the numerous orbital electrons, marked differences between the transmission of neutrons and the transmission of photons through a specimen may take place. Keypoints: Neutrons interact only with the nuclei of the atoms in the specimen Charlie Chong/ Fion Zhang

24. Neutron Transmission Mathematically the relationship for neutron transmission looks much like that for photons, but the variation of the action site (electron orbits or nucleus) produces large differences in the amount of transmitted beam. For photons: I = Ioe–μ t Eq.1 x For Neutron I = Ioe–Nσt= Ioe–μ tEq.2 n Where I is the transmitted beam; Iois the incident beam; μxis the linear attenuation coefficient for photons; t is the thickness of specimen in the beam path; N is the number of atoms per cubic centimeter; σ is the neutron cross section of the particular material or isotope (a probability or effective area); and, μnis the macroscopic cross section (μn= Nσ). Charlie Chong/ Fion Zhang

25. For photons: I = Ioe–μ t For Neutron I = Ioe–Nσt= Ioe–μ t Eq.1 x Eq.2 n Where:  I is the transmitted beam;  Iois the incident beam;  μxis the linear attenuation coefficient for photons;  t is the thickness of specimen in the beam path;  N is the number of atoms per cubic centimeter;  σ is the microscopic neutron cross section of the particular material or isotope (a probability or effective area); and,  μnis the macroscopic cross section (μn= Nσ). Charlie Chong/ Fion Zhang

26. Neutron Transmission For photons: I = Ioe–μx t Eq.1 For Neutron I = Ioe–Nσt= Ioe–μn t Eq.2 t μx for γ & X ray Ioe–μxt Io I μnfor Neutron Ioe–μnt Charlie Chong/ Fion Zhang

27. Figure 1 provides a comparison of the change in attenuation with increasing atomic number for X rays (125 keV) and thermal (0.025 eV) neutrons (1:5000000) . Such comparisons indicate some of the advantages of using neutrons for radiography. One advantage is found in the imaging of certain low atomic number materials in some high atomic number matrices. Photon radiography works best for the opposite circumstances. Neutrons can image a high cross section element in a low cross section matrix (an element's cross section is its total probability per atom for scattering or absorbing a unit of applied energy), such as cadmium in tin or in lead. Even changes in the isotopic composition of some elements can be imaged because cross sections of the isotopes may be different. Charlie Chong/ Fion Zhang

28. Keywords:  an element's cross section is its total probability per atom for (1) scattering or (2) absorbing a unit of applied energy.  Macro cross section = number of nuclide per cm3x micro cross section Charlie Chong/ Fion Zhang

29. FIGURE 1. Mass Attenuation Coefficients for the Elements (as a Function of Atomic Number) for Thermal Neutrons (Black Dots) and X-rays (Solid Line, X-ray Energy about 125 kVJ.) Charlie Chong/ Fion Zhang

30. Neutrons can image a high cross section element in a low cross section matrix (an element's cross section is its total probability per atom for scattering or absorbing a unit of applied energy), such as cadmium in tin or in lead. Charlie Chong/ Fion Zhang

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33. Mass-attenuation coefficient (cm2g-1) for the elements as a function of atomic number for both X-rays (solid line) and thermal neutrons (circles). Charlie Chong/ Fion Zhang

34. cadmium hydrogen/boron gadolinium samarium/europium beryllium/ water fixed energy of 150KV Charlie Chong/ Fion Zhang

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39. Z A Charlie Chong/ Fion Zhang

40. Neutron Radiography There is a marked difference between the photon radiography and neutron radiography; In neutron radiography, the neutrons interact only with the nuclei of the atom in the specimen not the numerous orbiting electrons. for Photon: I = Ioe-u t Where μx = linear attenuation coefficient for photon x for Neutron I = Ioe-Nσt Where σN = macro cross section = μn N= number of atom /cm3 σ = neutron microscopic cross section of the material I = Ioe-u t n Charlie Chong/ Fion Zhang

41. Radioactive Objects An additional advantage of neutron radiography is its ability to radiograph specimens that are intense sources of photons (radioactive specimens). The neutrons transmitted through a radioactive specimen will strike a metal detection foil such as indium, dysprosium or gold, rather than a converter screen with film. Atomic nuclei in the metal screen absorb neutrons to produce short-lived radioactive isotopes. After removal from the neutron beam, the decay of radioisotopes in the screen exposes a film, giving an autoradiograph of the specimen. Charlie Chong/ Fion Zhang

42. The neutrons transmitted through a radioactive specimen will strike a metal detection foil such as indium, dysprosium or gold, rather than a converter screen with film. Charlie Chong/ Fion Zhang

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44. lmaging Neutron radiographs usually are recorded on conventional X-ray film . Although neutrons have little direct effect on film, many techniques have been devised to convert neutrons into radiations that will expose a film or produce light for a real-time imaging system. These converter screens are similar to the intensifying screens used in photon radiography. Disadvantages Disadvantages of neutron radiography include (1) the high cost of the sources, (2) the relatively large size of the most practical neutron source assemblies, and (3) the personnel protection and safeguard problems associated with neutrons. These disadvantages combine to yield a major limitation of the technique; no really portable, inexpensive system is available. Nevertheless, equipment to produce neutron radiographs is available; in special circumstances, the unique information provided by neutron radiography outweighs the disadvantages. Charlie Chong/ Fion Zhang

45. Applications Such critical areas as the inspection of:  aerospace components,  explosives,  adhesive components,  nuclear control materials and nuclear fuel are examples of applications making use of neutron radiography's advantages. Neutron radiography is also useful for  the detection of corrosion (particularly in aircraft structures) and  for locating areas of water entrapment and hydrogen embrittlement. Charlie Chong/ Fion Zhang

46. Disciussion Subject: Disadvantages of neutron radiography include (1) the high cost of the sources, (2) the relatively large size of the most practical neutron source assemblies, and (3) the personnel protection and safeguard problems associated with neutrons. Charlie Chong/ Fion Zhang

47. PAR T 2 EQUIPMENT AND PR OCEDUR ES Charlie Chong/ Fion Zhang

48. 2.1 Neutron Sources The two main constituents of the nucleus are the proton and the neutron. The force between any pair of these particles is (1) strong, (2) attractive, and (3) of very short range; stable nuclei must have an external source of energy supplied for a separation of particles to occur. Any nucleus can be disrupted if adequate energy is supplied, but several light materials as well as several heavy materials can be made to yield free neutrons by supplying only moderate amounts of energy to their nuclei. A very limited number of materials emit neutrons during the spontaneous disruption of their nuclei. The general types of reactions used for neutron production are outlined below. Charlie Chong/ Fion Zhang

49. ■ Fission When a neutron enters a nucleus, the new (compound) nucleus gains an energy equal to the sum of the binding energy and the kinetic energy of the neutron. For some heavy isotopes, the addition of the binding energy of a neutron is sufficient to cause instability leading to nuclear fission. There can be, on the average, more than one free neutron produced per neutron absorbed, in assemblies containing fissionable materials. This net gain in free neutrons makes a nuclear chain reaction possible and is the basis for the more prolific neutron sources in general use. Isotopes most commonly used in fission reactors are U-235 and Pu-239. Keywords: Biding energy Kinetic energy Prolific neutron source Charlie Chong/ Fion Zhang

50. U-235 and Pu-239. Charlie Chong/ Fion Zhang