Radiography in Modern Industry - Kodak

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each separate radiograph may seem laborious, but it prevents invalidation of the measurementby an unnoticed or unavoidable variation in radiographic technique.The kilovoltage used should be as low as considerations of exposure time permit, for the sake ofincreased subject contrast, resulting in a higher accuracy of the measurements. By the sametoken, radiographs should be exposed to the highest density the available densitometer can readreliably. Because the contrast of industrial x-ray films increases with density (see "TheCharacteristic Curve"), the accuracy of the thickness measurement likewise increases withdensity.Special precautions should be observed if the specimen is narrow, or if measurements are to bemade near the edges of a large specimen. In these cases, the specimen should be surroundedwith a lead mask (see "Masks and Diaphragms)", to prevent the unattenuated primary radiationfrom striking the film near the boundaries of the specimen. Otherwise, large errors can arise inthe thickness determinations.Determination of the composition of parts is a special application of this technique. For example,it might be possible for parts identical in appearance to be made of different alloys. In general,though not invariably, different alloys have different absorptions. Thus, if a part of knowncomposition is radiographed along with a part, or group of parts, being checked, a difference indensity between corresponding areas of the control and specimens indicates a difference incomposition. Note that identical densities merely make it highly probable, though not certain, thatthe compositions are the same. This test, of course, provides no information on heat treatment,crystal size, or the like.It is much more difficult to estimate the size of a void or inclusion in the direction of the radiation.The density of the radiographic indication of a void depends not only on its dimensions along thedirection of the beam, but also on its location within the thickness of the material and on itsshape. Thus, it is necessary to prepare, by a separate experiment, calibration curves of void sizeversus density for each of several locations within the depth of the specimen, and perhaps foreach of several shapes of void. In addition, the location of the void must be determined by one ofthe methods described in "Depth Localization Of Defects", in order to know which of the abovementionedcalibration curves should be used.Such estimates of the dimensions of inclusions can be further complicated if the chemicalcomposition and density, and hence the radiation absorption, of the inclusion is unknown.This procedure for measuring the dimensions of voids has been applied successfully but,because of the extreme care and large amount of preliminary work required, has been limited tospecimens of high value and to circumstances where all parts of the radiographic process couldbe kept under the most rigorous control.High Speed RadiographyExposure times of one-millionth of a second, or even less, can be achieved by the use ofspecially designed high-voltage generating equipment and x-ray tubes. Such exposure times aresufficiently short to "stop" the motion of projectiles, high-speed machinery, and the like (SeeFigure 95).Radiography in Modern Industry 154
Figure 95: High-speed x-ray pictures of the functioning of a 20 mm HEI shell.This apparatus differs from the usual industrial x-ray equipment in design of both the high-voltagegenerator and the x-ray tube. The generator contains large high-voltage condensers that aresuddenly discharged through the x-ray tube, giving a high-voltage pulse of very short duration.The x-ray tube has a cold cathode rather than the conventional heated filament. Emission fromthe cold cathode is initiated by means of a third electrode placed near it. When electron emissionhas started, the discharge immediately transfers to the target, which is of conventional design.The tube current may reach a value as high as 2000 amperes (two million milliamperes), butbecause of the extremely short times of exposure, the load on the focal spot is not excessive.Geometric EnlargementIn most radiography, it is desirable to have the specimen and the film as close together aspossible to minimize geometric unsharpness (See "Calculation Of Geometric Unsharpness"). Anexception to this rule occurs when the source of radiation is extremely minute, that is, a smallfraction of a millimetre, as for instance in a betatron. In such a case, the film may be placed at adistance from the specimen, rather than in contact with it. (See Figure 96.) Such an arrangementresults in an enlarged radiograph without introducing objectionable geometric unsharpness.Enlargements of as much as three diameters by this technique have been found to be useful inthe detection of structures otherwise invisible radiographically. Geometric enlargements ofseveral tens of times are feasible in microradiography (See "Enlargement of Microradiographs").Radiography in Modern Industry 155
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RadiographyinModernIndustry
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RadiographyinModernIndustryFOURTH E
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ContentsIntroduction...............
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Chapter 1: The Radiographic Process
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Intensifying ScreensX-ray and other
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makes it a very suitable material f
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Figure 6: Typical voltage waveforms
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Table I - Typical X-ray Machines an
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The wavelengths (or energies of rad
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Table III - Industrial Gamma-Ray So
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1. The source of light should be sm
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B and H in the Figure 13 show the e
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Figure 14: Geometric construction f
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Figure 17: Pinhole pictures of the
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The kilovoltage applied to the x-ra
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Figure 21: Schematic diagram of som
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kind of material radiographed, the
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instance, the kilovoltage may be fi
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The technique need not be limited t
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Chapter 5: Radiographic ScreensWhen
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Contact between the film and the le
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Figure 29: The number of electrons
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lead foil screens ran be retained w
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Figure 33: The sharpness of the rad
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Figure 34: Low density (right) is a
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such as a wall or floor, on the fil
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from this source. Since scatter als
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A filter reduces excessive subject
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Definite rules as to filter thickne
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0.010-inch front screen of value be
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Example: Suppose that with a given
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If the milliamperage remains consta
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espectively. In other words, a cons
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Any given exposure chart applies to
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Figure 46: Typical gamma-ray exposu
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where the slope of the characterist
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Figure 49: Characteristic curves of
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Figure 51: Characteristic curve of
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Nomogram MethodsIn Figure 54, the s
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Figure 56: Transparent overlay posi
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Figure 58: Overlay positioned so as
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The problem of radiographing a part
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Figure 62: System of lines drawn on
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Chapter 8: Radiographic Image Quali
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Film contrast refers to the slope (
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Hole Type PenetrametersThe common p
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of the same thickness as the specim
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Chapter 9: Industrial X-ray FilmsMo
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Figure 70 indicates the direction t
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the lead letters on a radiation-abs
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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
Page 117 and 118: Rapid Access to Processed Radiograp
Page 119 and 120: Figure 78: Film-feeding procedures
Page 121 and 122: Chapter 11: Process ControlUsers of
Page 123 and 124: 3. Age of the developer replenisher
Page 125 and 126: Figure 80: Control chart below for
Page 127 and 128: DiscussionDensitometric data and pr
Page 129 and 130: Figure 82: Plan of a manual x-ray p
Page 131 and 132: Figure 83: A schematic diagram of a
Page 133 and 134: loading-bench activities are carrie
Page 135 and 136: KODAK Quinone-Thiosulfate Intensifi
Page 137 and 138: Methylene-Blue MethodTwo variations
Page 139 and 140: KODAK Hypo Test Solution HT-2Avoird
Page 141 and 142: In summary, use of the test papers
Page 143 and 144: narrow angle would be very thick, e
Page 145 and 146: When radiation passes through a spe
Page 147 and 148: Figure 89: Demonstration of the eff
Page 149 and 150: Figure 90: The amount of gamma radi
Page 151 and 152: The radiograph exposed in the right
Page 153: To illustrate, let us assume that t
Page 157 and 158: Figure 97: Two methods of neutron r
Page 159 and 160: Duplicating RadiographsSimultaneous
Page 161 and 162: Sometimes, as when sets of referenc
Page 163 and 164: PhotofluorographyIn photofluorograp
Page 165 and 166: discontinuities or of segregation i
Page 167 and 168: from the camera or by reaching down
Page 169 and 170: Figure 106: Schematic diagram of th
Page 171 and 172: valuable technique, for instance, i
Page 173 and 174: The position of the spots is determ
Page 175 and 176: Powder Diffraction File, Internatio
Page 177 and 178: 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
Page 187 and 188: film fairly well. If high densities
Page 189 and 190: Density = 1.5 Density = 2.5Film Rel
Page 191 and 192: In most industrial radiography, the
Page 193 and 194: 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
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electrons by successive Compton int
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Development is essentially a chemic
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Chapter 19: ProtectionOne of the mo
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duct is brought into the x-ray room
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Radiography in Modern Industry - Kodak

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