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Understanding Neutron Radiography Reading VIII Part 1 of 2 13, 2016 August Post Exam Reading

Understanding Neutron Radiography Reading VIII Part 1 of 2 13, 2016 August Post Exam Reading

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Understanding Neutron Radiography Reading VIII Part 1 of 2 13, 2016 August Post Exam Reading

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  1. Understanding Neutron R adiography More on Neutron, R eading 2016-1– NR T My ASNT Level III, Pre-Exam Preparatory Self Study Notes 29 July 2016 Charlie Chong/ Fion Zhang

  2. NRT Source Charlie Chong/ Fion Zhang

  3. NRT Source Charlie Chong/ Fion Zhang

  4. Neutron Source 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_zhang@ qq.com, c=CN 日期：2016.07.31 17:23:18 +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

  10. Fion Zhang at Copenhagen Harbor 30thJuly 2016 Charlie Chong/ Fion Zhang

  11. 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

  12. 闭门练功 Charlie Chong/ Fion Zhang

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

  14. Charlie Chong/ Fion Zhang

  15. neutron Charlie Chong/ Fion Zhang http://www.nuclear-power.net/nuclear-power/reactor-physics/atomic-nuclear-physics/fundamental-particles/neutron/

  16. 1.0 A neutron is one of the subatomic particle that make up matter. In the universe, neutrons are abundant, making up more than half of all visible matter. It has no electric charge and a rest mass equal to 1.67493 × 10-27 kg— marginally greater than that of the proton but nearly 1839 times greater than that of the electron. The neutron has a mean square radius of about 0.8×10-15 m, or 0.8 fm, and it is a spin-½ fermion. The neutrons exist in the nuclei of typical atoms, along with their positively charged counterparts, the protons. Neutrons and protons, commonly called nucleons, are bound together in the atomic nucleus, where they account for 99.9 percent of the atom’s mass. Research in high-energy particle physics in the 20th century revealed that neither the neutron nor the proton is not the smallest building block of matter. Protons and neutrons have also their structure. Inside the protons and neutrons, we find true elementary particles called quarks. Within the nucleus, protons and neutrons are bound together through the strong force, a fundamental interaction that governs the behaviour of the quarks that make up the individual protons and neutrons. Charlie Chong/ Fion Zhang

  17. The quark structure of the neutron. The color assignment of individual quarks is arbitrary, but all three colors must be present. Forces between quarks are mediated by gluons. Charlie Chong/ Fion Zhang

  18. A nuclear stability is determined by the competition between two fundamental interactions. Protons and neutrons are attracted each other via strong force. On the other hand protons repel each other via the electric force due to their positive charge. Therefore neutrons within the nucleus act somewhat like nuclear glue, neutrons attract each other and protons , which helps offset the electrical repulsion between protons. There are only certain combinations of neutrons and protons, which forms stable nuclei. For example, the most common nuclide of the common chemical element lead (Pb) has 82 protons and 126 neutrons. Charlie Chong/ Fion Zhang

  19. Nuclear binding energy curve. Charlie Chong/ Fion Zhang

  20. Because of the strength of the nuclear force at short distances, the nuclear binding energy (the energy required to disassemble a nucleus of an atom into its component parts) of nucleons is more than seven orders of magnitude larger than the electromagnetic energy binding electrons in atoms. Nuclear reactions (such as nuclear fission or nuclear fusion) therefore have an energy density that is more than 10 000 000x that of chemical reactions. Knowledge of the behaviour and properties of neutrons is essential to the production of nuclear power. Shortly after the neutron was discovered in 1932, it was quickly realized that neutrons might act to form a nuclear chain reaction. When nuclear fission was discovered in 1938, it became clear that, if a fission reaction produced free neutrons, each of these neutrons might cause further fission reaction in a cascade known as a chain reaction. Knowledge of cross- sections (the key parameter representing probability of interaction between a neutron and a nucleus) became crucial for design of reactor cores and the first nuclear weapon (Trinity, 1945). Charlie Chong/ Fion Zhang

  21. Trinity, 1945 Charlie Chong/ Fion Zhang

  22. Trinity, 1945 Charlie Chong/ Fion Zhang

  23. 2.0 Discovery of the Neutron The story of the discovery of the neutron and its properties is central to the extraordinary developments in atomic physics that occurred in the first half of the 20th century. The neutron was discovered in 1932 by the English physicist James Chadwick, but since the time of Ernest Rutherford it had been known that the atomic mass number A of nuclei is a bit more than twice the atomic number Z for most atoms and that essentially all the mass of the atom is concentrated in the relatively tiny nucleus. The Rutherford’s model for the atom in 1911 claims that atoms have their mass and positive charge concentrated in a very small nucleus. Charlie Chong/ Fion Zhang

  24. The alpha particles emitted from polonium fell on certain light elements, specifically beryllium, an unusually penetrating radiation is produced. Charlie Chong/ Fion Zhang http://www.nuclear-power.net/nuclear-power/reactor-physics/atomic-nuclear-physics/fundamental-particles/neutron/

  25. An experimental breakthrough came in 1930 with the observation by Bothe and Becker. They found that if the very energetic alpha particles emitted from polonium fell on certain light elements, specifically beryllium, boron, or lithium, an unusually penetrating radiation was produced. Since this radiation was not influenced by an electric field (neutrons have no charge), they presumed it was gamma rays (but much more penetrating). It was shown (Curie and Joliot) that when a paraffin target with this radiation is bombarded, it ejected protons with energy about 5.3 MeV. Paraffin is high in hydrogen content, hence offers a target dense with protons (since neutrons and protons have almost equal mass, protons scatter energetically from neutrons). These experimental results were difficult to interpret. James Chadwick was able to prove that the neutral particle could not be a photon by bombarding targets other than hydrogen, including nitrogen, oxygen, helium and argon. Not only were these inconsistent with photon emission on energy grounds, the cross-section for the interactions was orders of magnitude greater than that for Compton scattering by photons. In Rome, the young physicist Ettore Majorana suggested that the manner in which the new radiation interacted with protons required a new neutral particle. Charlie Chong/ Fion Zhang

  26. The task was that of determining the mass of this neutral particle. James Chadwick chose to bombard boron with alpha particles and analyze the interaction of the neutral particles with nitrogen. These particular targets were chosen partly because the masses of boron and nitrogen were well known. Using kinematics, Chadwick was able to determine the velocity of the protons. Then through conservation of momentum techniques, he was able to determine that the mass of the neutral radiation was almost exactly the same as that of a proton. In 1932, Chadwick proposed that the neutral particle was Rutherford’s neutron. In 1935, he was awarded the Nobel Prize for his discovery. Charlie Chong/ Fion Zhang

  27. Sir J ames Chadwick Charlie Chong/ Fion Zhang

  28. Handsome Ettore Majorana Charlie Chong/ Fion Zhang

  29. Chadwick’s neutron chamber containing parallel disks of radioactive polonium and beryllium. Radiation is emitted from an aluminum window at the chamber’s end. Charlie Chong/ Fion Zhang

  30. 3.0 Structure of Neutron Neutrons and protons are classified as hadrons, subatomic particles that are subject to the strong force and as baryons since they are composed of three quarks. The neutron is a composite particle made of two down quarks with charge −⅓ e and one up quark with charge +⅔ e. Since the neutron has no net electric charge, it is not affected by eletric forces, but the neutron does have a slight distribution of electric charge within it. This results in non-zero magnetic moment (dipole moment) of the neutron. Therefore the neutron interacts also via electromagnetic interaction, but much weaker than the proton. The mass of the neutron is 939.565 MeV/c2, whereas the mass of the three quarks is only about 12 MeV/c2(only about 1% of the mass-energy of the neutron). Like the proton, most of mass (energy) of the neutron is in the form of the strong nuclear force energy (gluons). The quarks of the neutron are held together by gluons, the exchange particles for the strong nuclear force. Gluons carry the color charge of the strong nuclear force. Charlie Chong/ Fion Zhang

  31. The quark structure of the neutron. The color assignment of individual quarks is arbitrary, but all three colors must be present. Forces between quarks are mediated by gluons Charlie Chong/ Fion Zhang

  32. Like the proton, most of mass (energy) of the neutron is in the form of the strong nuclear force energy (gluons). (99%) Charlie Chong/ Fion Zhang

  33. Two down quarks with charge −⅓ e and one up quark with charge +⅔ e. Charlie Chong/ Fion Zhang

  34. Properties Of Neutrons Key properties of neutrons are summarized below:  Mean square radius of a neutron is ~ 0.8 x 10-15m (0.8 fermi)  The mass of the neutron is 939.565 MeV/c2 (E=mc2)  Neutrons are ½ spin particles – fermionic statistics  Neutrons are neutral particles – no net electric charge.  Neutrons have non-zero magnetic moment.  Free neutrons (outside a nucleus) are unstable and decay via beta decay. The decay of the neutron involves the weak interaction and is associated with a quark transformation (a down quark is converted to an up quark).  Mean lifetime of a free neutron is 882 seconds (i.e. half-life is 611 seconds ).  A natural neutron background of free neutrons exists everywhere on Earth and it is caused by muons produced in the atmosphere, where high energy cosmic rays collide with particles of Earth’s atmosphere.  Neutrons cannot directly cause ionization. Neutrons ionize matter only indirectly. Charlie Chong/ Fion Zhang

  35.  Neutrons can travel hundreds of feet in air without any interaction. Neutron radiation is highly penetrating.  Neutrons trigger the nuclear fission.  The fission process produces free neutrons (2 or 3).  Thermal or cold neutrons have the wavelengths similar to atomic spacing. They can be used in neutron diffraction experiments to determine the atomic and/or magnetic structure of a material. Charlie Chong/ Fion Zhang

  36. It is known the fission neutrons are of importance in any chain-reacting system. Neutrons trigger the nuclear fission of some nuclei (235U, 238U or even 232Th). What is crucial the fission of such nuclei produces 2, 3 or more free neutrons. But not all neutrons are released at the same time following fission. Even the nature of creation of these neutrons is different. From this point of view we usually divide the fission neutrons into two following groups:  Prompt Neutrons. Prompt neutrons are emitted directly from fission and they are emitted within very short time of about 10-14second.  Delayed Neutrons. Delayed neutrons are emitted by neutron rich fission fragments that are called the delayed neutron precursors 先驱者 . These precursors usually undergo beta decay but a small fraction of them are excited enough to undergo neutron emission. The fact the neutron is produced via this type of decay and this happens orders of magnitude later compared to the emission of the prompt neutrons, plays an extremely important role in the control of the reactor. Charlie Chong/ Fion Zhang

  37. Beta Decay Charlie Chong/ Fion Zhang

  38. Table of key prompt and delayed neutrons characteristics. Thermal vs. Fast Fission Charlie Chong/ Fion Zhang

  39. Neutron Production – Prompt Neutrons. Charlie Chong/ Fion Zhang

  40. Energy release from 235U fission. Charlie Chong/ Fion Zhang

  41. Delayed Neutrons While the most of the neutrons produced in fission are prompt neutrons, the delayed neutrons are of importance in the reactor control. In fact the presence of delayed neutrons is perhaps most important aspect of the fission process from the viewpoint of reactor control. The term “delayed” in this context means, that the neutron is emitted with half-lifes, ranging from few milliseconds up to 55 s for the longest-lived precursor 87Br. These neutrons have to be distinguished from the prompt neutrons which are emitted immediately (on the order of 10-14s) after a fission event from a neutron-rich nucleus. Despite the fact the amount of delayed neutrons is only on the order of tenths of percent of the total amount, the timescale in seconds plays the extremely important role. Charlie Chong/ Fion Zhang

  42. Delayed neutrons are traditionally represented by six delayed neutron groups, whose yields and decay constants (λ) are obtained from nonlinear least- squares fits to experimental measurements. Charlie Chong/ Fion Zhang

  43. Key Characteristics of Delay Neutron  The presence of delayed neutrons is perhaps most important aspect of the fission process from the viewpoint of reactor control.  Delayed neutrons are emitted by neutron rich fission fragments that are called the delayed neutron precursors.  These precursors usually undergo beta decay but a small fraction of them are excited enough to undergo neutron emission.  The emission of neutron happens orders of magnitude later compared to the emission of the prompt neutrons.  About 240 neutron emitters are known between 8He and 210Tl, about 75 of them are in the non-fission region.  In order to simplify reactor kinetic calculations it is suggested to group together the precursors based on their half-lives.  Therefore delayed neutrons are traditionally represented by six delayed neutron groups. Charlie Chong/ Fion Zhang

  44.  Neutrons can be produced also in (γ, n) reactions (especially in reactors with heavy water moderator) and therefore they are usually referred to as photoneutrons. Photoneutrons are usually treated no differently than regular delayed neutrons in the kinetic calculations.  The total yield of delayed neutrons per fission, vd, depends on:  Isotope, that is fissioned.  Energy of a neutron that induces fission.  Variation among individual group yields is much greater than variation among group periods.  In reactor kinetic calculations it is convenient to use relative units usually referred to as delayed neutron fraction (DNF).  At the steady state condition of criticality, with keff = 1, the delayed neutron fraction is equal to the precursor yield fraction β.  In LWRs the β decreases with fuel burnup. This is due to isotopic changes in the fuel. Charlie Chong/ Fion Zhang

  45.  Delayed neutrons have initial energy between 0.3 and 0.9 MeV with an average energy of 0.4 MeV.  Depending on the type of the reactor, and their spectrum, the delayed neutrons may be more (in thermal reactors) or less effective than prompt neutrons (in fast reactors). In order to include this effect into the reactor kinetic calculations the effective delayed neutron fraction – βeffmust be defined.  The effective delayed neutron fraction is the product of the average delayed neutron fraction and the importance factor βeff= β . I.  The weighted delayed generation time is given by τ = ∑iτi. βi/ β = 13.05 s, therefore the weighted decay constant λ = 1 / τ ≈ 0.08 s-1.  The mean generation time with delayed neutrons is about ~0.1 s, rather than ~10-5as in section Prompt Neutron Lifetime, where the delayed neutrons were omitted.  Their presence completely changes the dynamic time response of a reactor to some reactivity change, making it controllable by control systems such as the control rods. Charlie Chong/ Fion Zhang

  46. Delay Neutron- Their presence completely changes the dynamic time response of a reactor to some reactivity change, making it controllable by control systems such as the control rods. Charlie Chong/ Fion Zhang

  47. Delay Neutron- Their presence completely changes the dynamic time response of a reactor to some reactivity change, making it controllable by control systems such as the control rods. Charlie Chong/ Fion Zhang

  48. Delayed neutrons originate from the radioactive decay of nuclei produced in fission and hence they are different for each fissile material. They are emitted by excited neutron rich fission fragments (so called the delayed neutron precursors) some appreciable time after the fission. How long afterward, is dependent on the half-life of the precursor, since the neutron emission itself occurs in a very short time. The precursors usually undergo beta decay without any neutron emission but a small fraction of them (highly excited nuclei) can undergo the neutron emission instead of the gamma emission. In addition current nuclear physics facilities can produce more neutron-rich isotopes that can emit multiple neutrons. Currently about 18 2n-emitters are experimentally confirmed [IAEA – INDC(NDS)-0599], but only two of them are also fission products. Charlie Chong/ Fion Zhang

  49. As an example, the isotope 87Br is the major component of the first group of precursor nuclei. This isotope has half-life of 55.6 seconds. It undergoes negative beta decay through its two main branches with emission of 2.6 MeV and 8 MeV beta particles. This decay leads to the formation of 87Kr* and 87Kr (ground state) and the87Kr nucleus subsequently decays via two successive beta decays into the stable isotope 87Sr. But there is also one possible way for the 87Br nucleus to beta decay. The 87Br nucleus can beta decay into an excited state of the 87Kr nucleus at an energy of 5.5 MeV, which is larger than the binding energy of a neutron in the 87Kr nucleus. In this case, the 87Kr nucleus can undergo (with probability of 2.5%) a neutron emission leading to the formation of stable 87Kr isotope. Charlie Chong/ Fion Zhang

  50. Precursors of Delayed Neutrons Charlie Chong/ Fion Zhang

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