Radiography in Modern Industry - Kodak

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On Speed And Contrast"). However, to use manual processing as an example, the minimumrecommended development time gives most of the available density and contrast. With certain ofthe direct x-ray film types, somewhat higher speed and, in same cases, slightly more contrast aregained by extending the development, but in no case should the maximum time recommended bythe manufacturer be exceeded.A special case arises when, for technical or economic reasons, there is a maximum allowableexposure time, that is, exposure time cannot be increased to take advantage of a higher filmgradient at higher densities. In such a case, an increase in kilovoltage increases the radiationintensity penetrating the specimen, and hence the film is exposed to a higher density. This mayresult in an increase in radiographic contrast. An example may be taken from the exposures usedto produce the exposure chart shown in Figure 44. The following table lists the densities obtainedthrough the 1/2-inch to 5/8-inch sections, using an exposure of 8 mA-min.kVD B1 / 2 in.steelD A5 / 8 in. steelRadiographic ContrastD B-D ARelative RadiographicContrast120 0.50 0.27 0.23 20140 1.20 0.67 0.53 46160 2.32 1.30 1.02 88180 3.48 2.32 1.16 100These data show that, when the exposure time is fixed, the density difference between the twosections increases, and hence the visibility of detail in this thickness range is also improved asthe kilovoltage is raised. The improvement in visibility of detail occurs in spite of the decrease inthe subject contrast caused by the increase in kilovoltage, and is the direct result of using higherdensities where the gradient of the film is higher. Qualitatively, one may say that, in this particularcase, the film contrast is increasing faster as a result of increased density than the subjectcontrast is decreasing as a result of increased kilovoltage. It should be emphasized again thatthis change in radiographic contrast resulting from a change in kilovoltage is not the result of achange in shape of the characteristic curve but rather the result of using a different portion of thecharacteristic curve--a portion where the slope is greater.SpeedFilm contrast depends on the shape of the characteristic curve. The other significant valueobtained from the characteristic curve is the relative speed, which is governed by the location ofthe curve, along the log E axis, in relation to the curves of other films.In Figure 16 the curves for the various x-ray films are spaced along the log relative exposure axis.The spacing of the curves arises from the differences in relative speed--the curves for the fasterfilms lying toward the left of the figure, those for the slower films toward the right. From thesecurves, relative exposures to produce a fixed density can be read; the relative speeds areinversely proportional to these exposures. For some industrial radiographic purposes, a density of1.5 is an appropriate level at which to compute relative speeds. However, the increasing trendtoward high densities, with all radiographs viewed on high-intensity illuminators, makes a densityof 2.5 more suitable for much industrial radiography. Relative speed values derived from thecurves in Figure 116 for the two density levels are tabulated in the next table where Film X hasarbitrarily been assigned a relative speed of 100 at both densities.Radiography in Modern Industry 188
Density = 1.5 Density = 2.5Film Relative Speed Relative Exposure for D = 1.5 Relative Speed Relative Exposure for D = 2.5X 100 1.0 100 1.0Y 24 4.2 26 3.9Z 250 0.4 150 0.7Note that the relative speeds computed at the two densities are not the same because of thedifferences in curve shape from one film to another. As would be expected from an inspection ofthese curves, this is most noticeable for Film Z.Although the shape of the characteristic curve of a film is practically independent of changes inradiation quality, the location of the curve along the log relative exposure axis, with respect to thecurve of another film, does depend on radiation quality. Thus, if curves of the type mentionedabove were prepared at a different kilovoltage, the curves would be differently spaced, that is, thefilms would have different speeds relative to the film that was chosen as a standard of reference.Density-Exposure RelationThe most common way of expressing the relation between film response and radiation intensity isthe characteristic curve--the relation between the density and the logarithm of the exposure--which has been discussed above. If, however, density is plotted against relative exposure to x-rays or gamma rays--rather than against the logarithm of the exposure--in many cares there is alinear relation over a more or less limited density range (See Figure 119). If net density (that is,density above base density and fog), rather than gross density, is plotted against exposure, thestraight line passes through the origin.Figure 119: Density versus exposure curve for a typical industrial x-ray film exposed todirect x-rays or with lead screens. The density range over which a linear relationshipexists between density and exposure depends on both the film type and the development.The linear relation cannot be assumed, however, but must be checked for the conditions involvedin the particular application because the density range over which it is valid depends on the filmRadiography in Modern Industry 189
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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
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5. Avoid pressure damage caused by
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Paddles or plunger-type agitators a
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slow, and the development time reco
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ubbles make their way to the surfac
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When development is complete, the f
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soften considerably with prolonged
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Figure 77: The roller transport sys
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Rapid Access to Processed Radiograp
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Figure 78: Film-feeding procedures
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Chapter 11: Process ControlUsers of
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3. Age of the developer replenisher
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Figure 80: Control chart below for
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DiscussionDensitometric data and pr
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Figure 82: Plan of a manual x-ray p
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Figure 83: A schematic diagram of a
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loading-bench activities are carrie
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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 and 154: To illustrate, let us assume that t
Page 155 and 156: Figure 95: High-speed x-ray picture
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: film fairly well. If high densities
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
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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