Understanding Neutron Radiography

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Interference Radiation Controlling unwanted interference radiation is a more complex problem for neutron radiography than for X-ray or gamma ray radiography. The usual problem, which includes scattering from all structural materials (including back-scattering), must be evaluated and controlled. However, neutron radiography is also subject to interference from neutrons which penetrate the collimator walls, secondary radiation from neutron capture in structural materials, and from gamma-ray contamination in the primary neutron beam. Direct exposure imaging techniques are normally useful only in cases where the neutron radiographic beam has a relatively low component of electromagnetic radiation. A high gamma-ray background can greatly reduce the radiographic contrast of low atomic number materials in the inspection object. For medium speed X-rayfilms, direct metal screen-film image detectors give about the same exposure from 10 5 n/cm 2 as from 1 milliroentgen (mR) of Co-60 gamma radiation. The exact ratio of neutron and gamma-ray response depends on the film and screen used. Charlie Chong/ Fion Zhang
Beam Tailoring A neutron beam extracted directly from a source assembly without altering its basic content is called a raw or unfiltered neutron beam. <strong>Neutron</strong> radiographs are usually made with such beams because they give satisfactory results for most applications and they require the least effort to produce. Specially tailored neutron beams should be considered for neutron radiography only when unfiltered beams do not give the desired results. ■ Gamma Filtration Generally, the gamma rays in a neutron beam do not cause serious interference problems in neutron radiographs. However, some neutron sources have inherently high gamma background because of special materials used in the assembly. Because some applications require a very low gamma background, gamma-ray filtration in the neutron beam should be considered. The most commonly used material for gamma filtration is bismuth; lead can also be used. The required thickness of the gamma filter is strongly dependent on the intensity and energy of the photons in the beam. Charlie Chong/ Fion Zhang
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Understanding Neutron Radiography R
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Military Applications Charlie Chong
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Military Applications Charlie Chong
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Charlie Chong/ Fion Zhang
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3. Techniques/Calibrations • Bloc
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Greek Alphabet Charlie Chong/ Fion
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Reading I SECTION 12-Neutron Radiog
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The text includes helpful discussio
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PART 1 PRINCIPLES OF NEUTRON RADIOG
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Advantages lt is the differences be
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For photons: I = I o e -μx t For N
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Figure 1 provides a comparison of t
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FIGURE 1. Mass Attenuation Coeffici
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Neutron Radiography There is a mark
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hydrogen/boron beryllium/ water cad
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Radioactive Objects An additional a
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lmaging Neutron radiographs usually
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PART 2 EQUIPMENT AND PROCEDURES Cha
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■ Fission When a neutron enters a
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U-235 and Pu-239. Charlie Chong/ Fi
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U-235 and Pu-239. Charlie Chong/ Fi
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Alpha Particles Charlie Chong/ Fion
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Alpha Particles Charlie Chong/ Fion
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Photoneutrons The necessary energy
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Radioactive Decay Charlie Chong/ Fi
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2.2 Neutron Energies As with all pe
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Thermal Neutrons “Produced by slo
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There are applications in which the
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FIGURE 2. Neutron Radiographs of Hi
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Fast Neutrons “Fast neutrons prov
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Moderators A complete description o
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TABLE 2. Slowing Down Properties of
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TABLE 3. Some Thermallzatlon Factor
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2.4 Neutron Collimation Beam extrac
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FIGURE 4. Neutron Collimators: (a)
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Divergent Collimators The primary a
Page 81 and 82: As in X- radiography, the geometric
Page 83 and 84: Geometric Unsharpness (neutron radi
Page 85 and 86: I ≈ Ф 16(L/D) 2 for my ASNT exam
Page 87 and 88: Backscatter It is good practice to
Page 89 and 90: TABLE 4. Average Characteristics of
Page 91 and 92: Nuclear Reactor The majority of pra
Page 93 and 94: Accelerators Numerous nuclear react
Page 95 and 96: (d.T) Source A reaction that has re
Page 97 and 98: Nuclear physicist at the Idaho Nati
Page 99 and 100: The gas pressure in the ion source
Page 101 and 102: (X.n) Sources Electron accelerators
Page 103 and 104: The threshold energy for photoneutr
Page 105 and 106: Bremsstrahlung , from bremsen "to b
Page 107 and 108: Characteristic x-rays are emitted f
Page 109 and 110: The frequencies of the characterist
Page 111 and 112: "Bremsstrahlung" means "braking rad
Page 113 and 114: Bohr’s Model Charlie Chong/ Fion
Page 115 and 116: Bohr’s Model Charlie Chong/ Fion
Page 117 and 118: Electron Orbital Charlie Chong/ Fio
Page 119 and 120: Plasma Sources Radiography with fas
Page 121 and 122: TABLE 5. Some Radloaalve Sources fo
Page 123 and 124: TABLE 5. Some Radloaalve Sources fo
Page 125 and 126: ■ (γ,n) Sources The (γ,n) react
Page 127 and 128: ■ Cf-252 On the basis of technica
Page 129 and 130: Subcritical Flux Boosters By defint
Page 131: Neutron Intensity Very few, if any,
Page 135 and 136: Foil Filters Some materials have sp
Page 137 and 138: ■ Window Filters For some element
Page 139 and 140: Fig.14-5 The neutron yield strongly
Page 141 and 142: ■ Time of Flight It is possible t
Page 143 and 144: 2.7 Neutron Image Detectors All the
Page 145 and 146: FIGURE 5. Diagrams for Neutron Radi
Page 147 and 148: TABLE 6. Properties of Some Thermal
Page 149 and 150: ■ Transfer Method In the transfer
Page 151 and 152: Transfer Method Examples Transfer r
Page 153 and 154: ■ Exposures, Contrast, Resolution
Page 155 and 156: ■ Reciprocity-Law Failure Scintil
Page 157 and 158: ■ Neutron-Gamma Response One impo
Page 159 and 160: ■ Real-Time Neutron Image Detecti
Page 161 and 162: ■ Other Detectors for Thermal Neu
Page 163 and 164: ■ Track-Etch Results The track-et
Page 165 and 166: 1) Epithermal Neutrons Work with ne
Page 167 and 168: 3) Fast Neutrons The other energy r
Page 169 and 170: As an example, copper screens are o
Page 171 and 172: ■ Detector Discussion Image detec
Page 173 and 174: 3.1 General General applications fo
Page 175 and 176: FIGURE 6. Radiographs of Explosive
Page 177 and 178: FIGURE 7. Thermal Neutron Radiograp
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3.8 Nuclear Industry Nuclear applic
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PART 4 NEUTRON RADIOGRAPHY STANDARD
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4.2 System Performance Standards St
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Those sources of radiation subject
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■ Personnel Protection All NRC li
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5.1 Neutron cross sections Neutron
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TABLE 9. Thermal Neutron Linear Att
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As an example, consider the calcula
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FIGURE 10. Half-Value Layers of Sel
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FIGURE 11. Tenth-Value Layers of Se
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5.3 Tenth-Value Layers There will b
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End Of Reading Charlie Chong/ Fion
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Source of Neutrons Charlie Chong/ F
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Radioactive Decay Interactive http:
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Source of Neutrons-Beta Decay Decay
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Source of Neutrons 236 U 92 ? Charl
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Radioactive Decay Charlie Chong/ Fi
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http://periodictable.com/Isotopes/0
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Neutron Energy & Detectability Slow
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Neutron Energy & Detectability Slow
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■ωσμ∙Ωπ∆º≠δ≤>ηθ
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Good Luck Charlie Chong/ Fion Zhang
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Understanding Neutron Radiography

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