Understanding Neutron Radiography

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■ Gadolinium Direct Exposures The most widely used detection method for industrial neutron radiography is the direct exposure technique with a gadolinium conversion screen. A typical arrangement is a single 25.4 μm (0.001 in.) thick gadolinium metal foil in a back screen configuration. In this case it is desirable to use a single emulsion film (as opposed to normal, double emulsion X-ray film). The low-energy internal conversion electrons emitted from the gadolinium upon neutron bombardment essentially expose only the emulsion facing the gadolinium. The elimination of the second film emulsion, therefore, reduces the detector response to thermal neutrons only slightly while substantially reducing the detector response to the gamma or X-radiation components of the radiation beam. Slow speed X-ray films with single emulsions are available from several manufacturers. Charlie Chong/ Fion Zhang
■ Exposures, Contrast, Resolution A typical thermal neutron exposure for a slow, single-emulsion, X-ray film and a single gadolinium conversion screen is about 3 X 109 n/cm2 . This can be reduced to about 108 n/cm2 for a fast X-ray film. In addition, some increase in speed can be obtained by using double gadolinium screens (a 6 μm front screen and a 50 μm thick back screen combination has provided good results) or a rhodium-gadolinium converter screen combination with double emulsion films. The single gadolinium conversion method has provided excellent spatial resolution in thermal neutron radiographs. An experimental spatial resolution value of 10 μm has been reported, in reasonable agreement with theoretical analyses. The contrast capability of the direct exposure method is usually somewhat poorer than that of the transfer method, because fogging radiation is often present. A typical thickness sensitivity for 25 mm steel or uranium objects is 2 percent. 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
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As in X- radiography, the geometric
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Geometric Unsharpness (neutron radi
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I ≈ Ф 16(L/D) 2 for my ASNT exam
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Backscatter It is good practice to
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TABLE 4. Average Characteristics of
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Nuclear Reactor The majority of pra
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Accelerators Numerous nuclear react
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(d.T) Source A reaction that has re
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Nuclear physicist at the Idaho Nati
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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 and 132: Neutron Intensity Very few, if any,
Page 133 and 134: Beam Tailoring A neutron beam extra
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: Transfer Method Examples Transfer r
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
Page 183 and 184: 3.8 Nuclear Industry Nuclear applic
Page 185 and 186: PART 4 NEUTRON RADIOGRAPHY STANDARD
Page 187 and 188: 4.2 System Performance Standards St
Page 189 and 190: Those sources of radiation subject
Page 191 and 192: ■ Personnel Protection All NRC li
Page 193 and 194: 5.1 Neutron cross sections Neutron
Page 195 and 196: TABLE 9. Thermal Neutron Linear Att
Page 197 and 198: As an example, consider the calcula
Page 199 and 200: FIGURE 10. Half-Value Layers of Sel
Page 201 and 202: 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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