Radiography in Modern Industry - Kodak

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Figure 124 shows the number of roentgens needed to produce a density of 1.0 on a particular x-ray film under certain processing conditions. (Exposures were made without screens, eitherfluorescent or lead.)The spectral sensitivity curves for all x-ray films have roughly the same general features as thecurves shown in Figure 124. Details, among them the ratio of maximum to minimum sensitivity,differ from type to type of film, however.The spectral sensitivity of a film, or differences in spectral sensitivity between two films, needrarely be considered in industrial radiography. Usually, such changes in sensitivity areautomatically taken into account in the preparation of exposure charts See "Preparing AnExposure Chart") and of tables of relative film speeds. The spectral sensitivity of a film is, ofcourse, very important in radiation monitoring, because in this case an evaluation of the numberof roentgens incident on the film is required.Figure 124: Typical x-ray spectral sensitivity curve of an x-ray film, showing the number ofroentgens required to produce a density of 1.0 for various radiation qualities. Other filmswill have curves of similar shape, but shifted up or down depending on the properties ofthe film and the development technique used. (After Wilsey, Radiography, 56:229, 1951.)Radiography in Modern Industry 194
Chapter 17: Film Graininess; Signal-to-Noise Ratio inRadiographsGraininessGraininess is defined as the visual impression of nonuniformity of density in a radiographic (orphotographic) image. With fast films exposed to high-kilovoltage radiation, the graininess is easilyapparent to the unaided vision; with slow films exposed to low-kilovoltage x-rays, moderatemagnification may be needed to make it visible. In general, graininess increases with increasingfilm speed and with increasing energy of the radiation.The "clumps" of developed silver, which are responsible for the impression of graininess do noteach arise from a single developed photographic grain. That this cannot be so can be seen fromsize consideration alone. The particle of black metallic silver arising from the development of asingle photographic grain in an industrial x-ray film (See Figure 69) is rarely larger than 0.001 mm(0.00004 inch) and usually even less. This is far below the limits of unaided human vision.Rather, the visual impression of graininess is caused by the random, statistical grouping of theseindividual silver particles. Each quantum (photon) of x-radiation or gamma radiation absorbed inthe film emulsion exposes one or more of the tiny crystals of silver bromide of which the emulsionis composed (See Figure 67). These "absorption events" occur at random and even in a uniformx-ray beam, the number of absorption events will differ from one tiny area of the film to the nextfor purely statistical reasons. Thus, the exposed grains will be randomly distributed; that is, theirnumbers will have a statistical variation from one area to the next.In understanding this effect, a simple analogy--a long sidewalk on a rainy day--will be ofassistance. The sidewalk corresponds to the film and the raindrops to the x-ray photons absorbedin it. (Only those absorbed by the film are considered because only those that are absorbed havea photographic effect.) First, consider what happens in a downpour so hard that there is anaverage of 10,000 drops per block or square of the sidewalk. It would not be expected, however,that each square would receive precisely this average number of 10,000 drops. Since theraindrops fall at random, only a few or perhaps none of the squares would receive precisely10,000 drops. Some would receive more than 10,000 and others less. In other words, the actualnumber of drops falling on any particular square will most likely differ from the average number ofdrops per square along the whole length of the sidewalk. The laws of statistics show that thedifferences between the actual numbers and the average number of drops can be described interms of probability. If a large number of blocks is involved, the actual number of raindrops on68 percent of the block, will differ from the average by no more than 100 drops or ±1 percent ofthe average. 1 The remaining 32 percent will differ by more than this number. Thus, thedifferences in "wetness" from one block of sidewalk to another will be small and probablyunnoticeable.This value of 100 drops holds only for an average of 10,000 drops per square. Now consider thesame sidewalk in a light shower in which the average number of drops per square is only 100.The same statistical laws show that the deviation from the average number of drops will be 10 or±10 percent of the average. Thus, differences in wetness from one square to the next will bemuch more noticeable in a light shower (±10 percent) than they are in a heavy downpour (±1percent).Now we will consider these drops as x-ray photons absorbed in the film. With a very slow film, itmight be necessary to have 10,000 photons absorbed in a small area to produce a density of, forexample, 1.0. With an extremely fast film it might require only 100 photons in the same area to
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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
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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
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 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: e noted here. Although the average
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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