Understanding Neutron Radiography

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The attenuation of neutrons however, is a function of the nucleus rather than the density of electrons in a material, and it is frequently found that adjacentnumber elements, for example boron and carbon, show marked differences in neutron-attenuation coefficient and are therefore readily discriminated. Hydrogen has a high neutron attenuation coefficient, and so it is possible to detect rubbers and plastics. Conversely dense materials such as lead and tungsten have low coefficients and a re readily penetrated by thermal neutrons. Thus we find that the two radiographic processes, X-ray and neutron, are often complementary. X-rays are stopped by dense materials and pass through light ones, and in many instances neutrons have the reverse qualities. Charlie Chong/ Fion Zhang
<strong>Neutron</strong>s will penetrate the body of a large metal valve to give a good image of an internal rubber seal. For the X- rays to record this seal would require a long exposure which would probably obliterate most of the other detail on the radiograph. However, if the valve were inside a thick polythene case then the X- rays would penetrate this with negligible attenuation, whereas the neutrons would have difficulty in producing a radiograph. Charlie Chong/ Fion Zhang Nares Chankow Department of Nuclear Engineering, Faculty of Engineering
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Understanding Neutron Radiography R
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Submarine Nuclear Pile Charlie Chon
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Charlie Chong/ Fion Zhang
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3. Techniques/Calibrations • Bloc
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Greek Alphabet sound A a [a] nu B [
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A Alpha r Gamma NNu T Tau (al-fah)
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INTRODUCTION Radiography with neutr
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1. PRINCIPLES AND PRACTICE OF NEUTR
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He had indentified a particle which
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BEPO stood for British Experimental
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They also demonstrated the applicat
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The radiographic process requires f
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1.1.3. Neutron Sources Neutrons are
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This energy varies with both the ta
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The reaction takes place, that is a
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The life and output of the target u
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There is considerable variation in
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1 .1 .3.2 Radioisotopes Radioisotop
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Fig. 1 .3 Isotopie Neutron Sources.
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Table 1.2 Radioisotopic Neutron Sou
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The nuclear reactor is an assembly
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or Cf 252 (spontaneous fission) //
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Neutron Source- Reactor .. "J ' ' '
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The Nuclear Chain Reaction Cs Neutr
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Source Radioisotopes, accelerator N
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Cf 252 (spontaneous fission) 1.0 af
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Spontaneous fission (SF) NucUde Hal
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Figure 2: Spontaneous Fission Spect
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This fission process produces a con
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Keywords: • effective multiplicat
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Fig. 1.5 Increase in Neutron Flux a
Page 65 and 66: Table 1.3 Summary of the Properties
Page 67 and 68: The unit of cross section is the 'b
Page 69 and 70: Charlie Chong/ Fion Zhang 10 4 10
Page 71 and 72: One isotope of cadmium, 113 Cd, abs
Page 73 and 74: This is given by -dФ /dx = ФσN (
Page 75 and 76: The ratio between these two neutron
Page 77 and 78: Neutron Attenuation Incident lntens
Page 79 and 80: PART 5 NEUTRON CROSS SECTIONS AND A
Page 81 and 82: For photons: I = I o e -μx t For N
Page 83 and 84: If on the other hand, the material
Page 85 and 86: Charlie Chong/ Fion Zhang σ C σ H
Page 87 and 88: FIGURE 10. Half-Value Layers of Sel
Page 89 and 90: 5.2 Half-Value Layers An important
Page 91 and 92: 5.4 CONCLUSION Neutron radiography
Page 93 and 94: A prime requirement for a moderator
Page 95 and 96: 1.1.4.3 Collimation Having produced
Page 97 and 98: An alternative method, widely used
Page 99 and 100: Charlie Chong/ Fion Zhang A. MULn-'
Page 101 and 102: As the flux gradient is usually sma
Page 103 and 104: Now the fraction of neutrons lost d
Page 105 and 106: for simplicity this can be expresse
Page 107 and 108: Hawkesworth found reasonable agreem
Page 109 and 110: To minimise unsharpness the apertur
Page 111 and 112: (f) the resolution improves with an
Page 113 and 114: Neutron generator Neutron collimato
Page 115: 1 .1 .5 Neutrons Applied to Radiogr
Page 119 and 120: Neutrons radiograph. I eutt·on(Gd/
Page 121 and 122: Neutrons radiograph. Charlie Chong/
Page 123 and 124: Neutrons radiograph Charlie Chong/
Page 125 and 126: 100 I Ill 100 .. N E 10 u Ī- z w -
Page 127 and 128: Attenuation Coefficients for Neutro
Page 129 and 130: 1 . 1 .6 Neutron Image Detectors Un
Page 131 and 132: The particular a dvantage of the ga
Page 133 and 134: Figure 2: (a) Silver Activated zinc
Page 135 and 136: 1.1 .6.2 Transfer Technique This me
Page 137 and 138: With the transfer method only the f
Page 139 and 140: Fig. 1.10 Irradiation /Transfer Cur
Page 141 and 142: Table 1.4 The Characteristics of So
Page 145 and 146: 1.1 .6.3 Dynamic Imaging Methods Th
Page 147 and 148: Fig. 1.11 Television System for Neu
Page 149 and 150: 1.1.7 Image Recorders At present th
Page 151 and 152: Development, on the other hand, pro
Page 153 and 154: The relationship between exposure a
Page 155 and 156: Fig. 1.12 Typical Characteristic Cu
Page 157 and 158: The steeper the slope of the curve
Page 159 and 160: Type Kodak Ltd. (U .K.) IIford Ltd
Page 163 and 164: Farny [Ref. 36] has made the follow
Page 165 and 166: ■ (a) (b) (c) (d) (e) (f) (g) Ind
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1. 1 .8 Film and Foil Relationships
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Table 1.4 The Characteristics of So
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The literature often describes meth
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Fig. 1 . 1 3 Measu rement of Unshar
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There are three types of unsharpnes
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This is a frequence response method
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This resolution is at the expense o
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Fig. 1 . 1 5 Contrast Transfer Func
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Ф = Ф o e -Σx where Ф = transmi
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For a metal foil detector D e = G
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Hawkesworth [Ref. 23] considered th
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Furthermore thermal neutrons are at
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1. 1 .9 Neutron Beam Filters Neutro
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(a) (b) (c) the ratio of 1 .4 eV ne
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Fig. 1 . 1 6 Resonance Curves for a
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1) J KEY TO RESONANCE TYPES A 8 c 0
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1.2 THE DESIGN OF NEUTRON RADIOGRAP
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Let us assume that your resolution
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Fig. 1.17 Van Der Graaff Accelerato
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The Van De Graaff Accelerator. Char
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Neutron Source: Linac Charlie Chong
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Neutron Source: Accelerator . I ' r
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1 .2.2 The Collimator 1 .2.2.1 Coll
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The L/D ratio of the collimator can
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Cadmium ratio - the ratio of the re
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Fig. 1.16 Resonance Curves for a Cd
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1) J KEY TO RESONANCE TYPES A B c 0
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1 .2.2.2 Characteristics of Lining
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Cadmium is readily available in foi
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106 '1017 108 10'9 11110 1 11 1 111
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Table 1.9 shows that the natura l m
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Isotopic Composition Emission Trans
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The appropriate thicknesses can be
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1 .2.2.5 Geometric Enlargement and
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Table 1.4 The Characteristics of So
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- Characteristics of Indium Indium
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Table 1.10 Data on Indium [Refs. 24
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- Characteristics of Dysprosium Dys
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1 Isoto pi ~c Compo:sition l.sotopi
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Table1 .12 Data on Gadolinium [Refs
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1 .2.3.2 Converter- Foil Thickness
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Fig. 1.18 Film Foil Geometry. EMULS
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So theoretically the unsharpness is
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Now, ignoring self-shielding, equat
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For the transfer data the foils wer
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Table 1. 14 Resolut ion Characteris
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Fig. 1.19 Build-Up of Activity i n
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1 .2.3.3 Film and Foil Resolution B
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Hot Charcoal Iron Charlie Chong/ Fi
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1 .3 A PPLICATIONS OF NEUTRON RADIO
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Fig. 1.20 Cross-Section of Pressure
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Fig. 1.21 Neutron Radiographs showi
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The detection technique is non-dest
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1.3.2 Industrial Applications Hydro
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Brazing and soldering meterials are
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Run-out on deep drilled holes occur
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F ig. 1. 25 X- Radiograph and Neutr
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1 .3.4 Other Applications Figure 1.
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Charlie Chong/ Fion Zhang http://ww
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• absorption coefficient: related
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• contrast agent: a material adde
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TABLE I. NeLib'ons Crasslrfled AA;c
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More Reading: (epithermal neutron)
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Neutron capture cross section for 1
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Maxwell-Boltzmann distribution In p
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Probability density function a=l 0"
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The Maxwell-Boltzmann distribution
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• filtered neutron beam: neutron
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• indirect exposure imaging: in t
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More reading on Mass absorption coe
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• neutron radiography: a process
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• sub-thermal neutrons:neutrons h
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Nuclei or Macroscopic Cross Section
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Nuclei or Maeto6CGpiC Cr066 Section
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where N =number density of stable i
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The required film density can be de
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N (number of nuclei cm -3 ) = ρN a
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Example of cellulose acetate C 6 H
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Charlie Chong/ Fion Zhang TABLE 9.
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Further Reading: Interesting Form h
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Peach - 我爱桃子 Charlie Cho
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Good Luck Charlie Chong/ Fion Zhang
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Understanding Neutron Radiography

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