Radiography in Modern Industry - Kodak

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Chapter 6: Scattered RadiationWhen a beam of x-rays or gamma rays strikes any object, some of the radiation is absorbed,some is scattered, and some passes straight through. The electrons of the atoms constituting theobject scatter radiation in all directions, much as light is dispersed by a fog. The wavelengths ofmuch of the radiation are increased by the scattering process, and hence the scatter is alwayssomewhat "softer," or less penetrating, than the unscattered primary radiation. Any material--whether specimen, cassette, tabletop, walls, or floor--that receives the direct radiation is a sourceof scattered radiation. Unless suitable measures are taken to reduce the effects of scatter, it willreduce contrast over the whole image or parts of it.Scattering of radiation occurs, and is a problem, in radiography with both x-rays and gamma rays.In the material that follows, the discussion is in terms of x-rays, but the same general principlesapply to gamma radiography.In the radiography of thick materials, scattered radiation forms the greater percentage of the totalradiation. For example, in the radiography of a 3/4-inch thickness of steel, the scattered radiationfrom the specimen is almost twice as intense as the primary radiation; in the radiography of a 2-inch thickness of aluminum, the scattered radiation is two and a half times as great as the primaryradiation. As may be expected, preventing scatter from reaching the film markedly improves thequality of the radiographic image.Figure 35: Sources of scattered radiation. A: Transmitted scatter. B: Scatter fromcassette. C: "Reflection" scatter.As a rule, the greater portion of the scattered radiation affecting the film is from the specimenunder examination (A in Figure 35). However, any portion of the film holder or cassette thatextends beyond the boundaries of the specimen and thereby receives direct radiation from the x-ray tube also becomes a source of scattered radiation, which can affect the film. The influence ofthis scatter is most noticeable just inside the borders of the image (B in Figure 35). In a similarmanner, primary radiation striking the film holder or cassette through a thin portion of thespecimen will cause scattering into the shadows of the adjacent thicker portions. Such scatter iscalled undercut. Another source of scatter that may undercut a specimen is shown as C in thefigure above. If a filter is used near the tube, this too will scatter x-rays. However, because of thedistance from the film, scattering from this source is of negligible importance. Any other material,
such as a wall or floor, on the film side of the specimen may also scatter an appreciable quantityof x-rays back to the film, especially if the material receives the direct radiation from the x-raytube or gamma-ray source (See Figure 36). This is referred to as backscattered radiation.Figure 36: Intense backscattered radiation may originate in the floor or wall. Coning,masking, or diaphragming should be employed. Backing the cassette with lead may giveadequate protection.Reduction Of ScatterAlthough scattered radiation can never be completely eliminated, a number of means areavailable to reduce its effect. The various methods are discussed in terms of x-rays. Althoughmost of the same principles apply to gamma-ray radiography, differences in application arisebecause of the highly penetrating radiation emitted by most common industrial gamma-raysources. For example, a mask (See Figure 37) for use with 200 kV x-rays could easily be lightenough for convenient handling. A mask for use with cobalt 60 radiation, on the other hand,would be thick, heavy, and probably cumbersome. In any event, with either x-rays or gammarays, the means for reducing the effects of scattered radiation must be chosen on the basis ofcost, convenience, and effectiveness.Radiography in Modern Industry 51
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Page 3 and 4: RadiographyinModernIndustryFOURTH E
Page 5 and 6: ContentsIntroduction...............
Page 7 and 8: Chapter 1: The Radiographic Process
Page 9 and 10: Intensifying ScreensX-ray and other
Page 11 and 12: makes it a very suitable material f
Page 13 and 14: Figure 6: Typical voltage waveforms
Page 15 and 16: Table I - Typical X-ray Machines an
Page 17 and 18: The wavelengths (or energies of rad
Page 19 and 20: Table III - Industrial Gamma-Ray So
Page 21 and 22: 1. The source of light should be sm
Page 23 and 24: B and H in the Figure 13 show the e
Page 25 and 26: Figure 14: Geometric construction f
Page 27 and 28: Figure 17: Pinhole pictures of the
Page 29 and 30: The kilovoltage applied to the x-ra
Page 31 and 32: Figure 21: Schematic diagram of som
Page 33 and 34: kind of material radiographed, the
Page 35 and 36: instance, the kilovoltage may be fi
Page 37 and 38: The technique need not be limited t
Page 39 and 40: Chapter 5: Radiographic ScreensWhen
Page 41 and 42: Contact between the film and the le
Page 43 and 44: Figure 29: The number of electrons
Page 45 and 46: lead foil screens ran be retained w
Page 47 and 48: Figure 33: The sharpness of the rad
Page 49: Figure 34: Low density (right) is a
Page 53 and 54: from this source. Since scatter als
Page 55 and 56: A filter reduces excessive subject
Page 57 and 58: Definite rules as to filter thickne
Page 59 and 60: 0.010-inch front screen of value be
Page 61 and 62: Example: Suppose that with a given
Page 63 and 64: If the milliamperage remains consta
Page 65 and 66: espectively. In other words, a cons
Page 67 and 68: Any given exposure chart applies to
Page 69 and 70: Figure 46: Typical gamma-ray exposu
Page 71 and 72: where the slope of the characterist
Page 73 and 74: Figure 49: Characteristic curves of
Page 75 and 76: Figure 51: Characteristic curve of
Page 77 and 78: Nomogram MethodsIn Figure 54, the s
Page 79 and 80: Figure 56: Transparent overlay posi
Page 81 and 82: Figure 58: Overlay positioned so as
Page 83 and 84: The problem of radiographing a part
Page 85 and 86: Figure 62: System of lines drawn on
Page 87 and 88: Chapter 8: Radiographic Image Quali
Page 89 and 90: Film contrast refers to the slope (
Page 91 and 92: Hole Type PenetrametersThe common p
Page 93 and 94: of the same thickness as the specim
Page 95 and 96: Chapter 9: Industrial X-ray FilmsMo
Page 97 and 98: Figure 70 indicates the direction t
Page 99 and 100: the lead letters on a radiation-abs
Page 101 and 102:
Therefore, protection requirements
Page 103 and 104:
5. Avoid pressure damage caused by
Page 105 and 106:
Paddles or plunger-type agitators a
Page 107 and 108:
slow, and the development time reco
Page 109 and 110:
ubbles make their way to the surfac
Page 111 and 112:
When development is complete, the f
Page 113 and 114:
soften considerably with prolonged
Page 115 and 116:
Figure 77: The roller transport sys
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Rapid Access to Processed Radiograp
Page 119 and 120:
Figure 78: Film-feeding procedures
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Chapter 11: Process ControlUsers of
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3. Age of the developer replenisher
Page 125 and 126:
Figure 80: Control chart below for
Page 127 and 128:
DiscussionDensitometric data and pr
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Figure 82: Plan of a manual x-ray p
Page 131 and 132:
Figure 83: A schematic diagram of a
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loading-bench activities are carrie
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KODAK Quinone-Thiosulfate Intensifi
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Methylene-Blue MethodTwo variations
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KODAK Hypo Test Solution HT-2Avoird
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In summary, use of the test papers
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narrow angle would be very thick, e
Page 145 and 146:
When radiation passes through a spe
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Figure 89: Demonstration of the eff
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Figure 90: The amount of gamma radi
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The radiograph exposed in the right
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To illustrate, let us assume that t
Page 155 and 156:
Figure 95: High-speed x-ray picture
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Figure 97: Two methods of neutron r
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Duplicating RadiographsSimultaneous
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Sometimes, as when sets of referenc
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PhotofluorographyIn photofluorograp
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discontinuities or of segregation i
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from the camera or by reaching down
Page 169 and 170:
Figure 106: Schematic diagram of th
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valuable technique, for instance, i
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The position of the spots is determ
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Powder Diffraction File, Internatio
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Processing TechniquesRadiographs on
Page 179 and 180:
Since this formula applies only to
Page 181 and 182:
such that it does not distort the i
Page 183 and 184:
Figure 113: A: Representation of a
Page 185 and 186:
Figure 115: Characteristic curve of
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film fairly well. If high densities
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Density = 1.5 Density = 2.5Film Rel
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In most industrial radiography, the
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e noted here. Although the average
Page 195 and 196:
Chapter 17: Film Graininess; Signal
Page 197 and 198:
The ratio of signal to noise has a
Page 199 and 200:
Chapter 18: The Photographic Latent
Page 201 and 202:
Thus, the change that makes an expo
Page 203 and 204:
Figure 130: Stages in the developme
Page 205 and 206:
electrons by successive Compton int
Page 207 and 208:
Development is essentially a chemic
Page 209 and 210:
Chapter 19: ProtectionOne of the mo
Page 211 and 212:
duct is brought into the x-ray room
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Radiography in Modern Industry - Kodak

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