Radiography in Modern Industry - Kodak

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Figure 126: Electron micrograph of exposed, partially developed, and fixed grains,showing initiation of development at localized sites on the grains (1µ = 1 micron = 0.001mm).It was further known that the material of the latent image was, in all probability, silver. For onething, chemical reactions that will oxidize silver will also destroy the latent image. For another, it isa common observation that photographic materials given prolonged exposure to light darkenspontaneously, without the need for development. This darkening is known as the print-outimage. The printout image contains enough material to be identified chemically, and this materialis metallic silver. By microscopic examination, the silver of the print-out image is discovered to belocalized at certain discrete areas of the grain (See Figure 127), just as is the latent image.Figure 127: Electron micrograph of photolytic silver produced in a grain by very intenseexposure to light.Radiography in Modern Industry 200
Thus, the change that makes an exposed photographic grain capable of being transformed intometallic silver by the mild reducing action of a photographic developer is a concentration of silveratoms--probably only a few--at one or more discrete sites on the grain. Any theory of latent-imageformation must account for the way that light photons absorbed at random within the grain canproduce these isolated aggregates of silver atoms. Most current theories of latent-imageformation are modifications of the mechanism proposed by R. W. Gurney and N. F. Mott in 1938.In order to understand the Gurney-Mott theory of the latent image, it is necessary to digress andconsider the structure of crystals--in particular, the structure of silver bromide crystals.When solid silver bromide is formed, as in the preparation of a photographic emulsion, the silveratoms each give up one orbital electron to a bromine atom. The silver atoms, lacking onenegative charge, have an effective positive charge and are known as silver ions (Ag+). Thebromine atoms, on the other hand, have gained an electron--a negative charge--and havebecome bromine ions (Br-). The "plus" and "minus" signs indicate, respectively, one fewer or onemore electron than the number required for electrical neutrality of the atom.A crystal of silver bromide is a regular cubical array of silver and bromide ions, as shownschematically in Figure 128. It should be emphasized that the "magnification" of the figure is verygreat. An average grain in an industrial x-ray film may be about 0.00004 inch in diameter, yet willcontain several billions of ions.Figure 128: A silver bromide crystal is a rectangular array of silver (Ag+) and bromide(Br-) ions.A crystal of silver bromide in a photographic emulsion is--fortunately--not perfect; a number ofimperfections are always present. First, within the crystal, there are silver ions that do not occupythe "lattice position" shown in the figure above, but rather are in the spaces between. These areknown as interstitial silver ions (See Figure 129). The number of the interstitial silver ions is, ofcourse, small compared to the total number of silver ions in the crystal. In addition, there aredistortions of the uniform crystal structure. These may be "foreign" molecules, within or on thecrystal, produced by reactions with the components of the gelatin, or distortions or dislocations ofthe regular array of ions shown in Figure 128. These may be classed together and called "latentimagessites."Radiography in Modern Industry 201
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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
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narrow angle would be very thick, e
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When radiation passes through a spe
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Figure 89: Demonstration of the eff
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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 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: Chapter 18: The Photographic Latent
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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