Radiography in Modern Industry - Kodak

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Figure 132: Characteristic curves plotted from the data in Figure 131.Because a grain is completely exposed by the passage of an energetic electron, all x-rayexposures are, as far as the individual grain is concerned, extremely short. The actual time thatan x-ray-induced electron is within a grain depends on the electron velocity, the grain dimensions,and the "squareness" of the hit. However, a time of the order of 10 -13 second is representative.(This is in distinction to the case of light where the "exposure time" for a single grain is the intervalbetween the arrival of the first photon and that of the last photon required to produce a stablelatent image.)The complete exposure of a grain by a single event and in a very short time implies that thereshould be no reciprocity-law failure for direct x-ray exposures or for exposures made with lead foilscreens. The validity of this has been established for commercially available film andconventional processing over an extremely wide range of x-ray intensities. That films cansatisfactorily integrate x-, gamma-, and beta-ray exposures delivered at a wide range ofintensities is one of the advantages of film as a radiation dosimeter.In the discussion on reciprocity-law failure it was pointed out that a very short, very high intensityexposure to light tends to produce latent images in the interior of the grain. Because x-rayexposures are also, in effect, very short, very high intensity exposures, they too tend to produceinternal, as well as surface, latent images.DevelopmentMany materials discolor on exposure to light--a pine board or the human skin, for example--andthus could conceivably be used to record images. However, most such systems reset to exposureon a "1:1" basis, in that one photon of light results in the production of one altered molecule oratom. The process of development constitutes one of the major advantages of the silver halidesystem of photography. In this system, a few atoms of photolytically deposited silver can, bydevelopment, be made to trigger the subsequent chemical deposition of some 10 9 or 10 10additional silver atoms, resulting in an amplification factor of the order of 10 9 or greater. Theamplification process can be performed at a time, and to a degree, convenient to the user and,with sufficient care, can be uniform and reproducible enough for the purposes of quantitativemeasurements of radiation.Radiography in Modern Industry 206
Development is essentially a chemical reduction in which silver halide is reduced or converted tometallic silver in order to retain the photographic image, however, the reaction must be limitedlargely to those grains that contain a latent image. That is, to those grains that have receivedmore than a certain minimum exposure to radiation. Compounds that can be used asphotographic developing agents, therefore, are limited to those in which the reduction of silverhalide to metallic silver is catalyzed (or speeded up) by the presence of the metallic silver of thelatent image. Those compounds that reduce silver halide in the absence of a catalytic effect bythe latent image are not suitable developing agents because they produce a uniform overalldensity on the processed film.Many practical developing agents are relatively simple organic compounds (See Figure 133) and,as shown, their activity is strongly dependent on molecular structure as well as on composition.There exist empirical rules by which the developing activity of a particular compound may oftenbe predicted from a knowledge of its structure.Figure 133: Configurations of dihydroxybenzene, showing how developer propertiesdepend on structure.The simplest concept of the role of the latent image in development is that it acts merely as anelectron-conducting bridge by which electrons from the developing agent can reach the silver ionson the interior face of the latent image. Experiment has shown that this simple concept isinadequate to explain the phenomena encountered in practical photographic development.Adsorption of the developing agent to the silver halide or at the silver-silver halide interface hasbeen shown to be very important in determining the rate of direct, or chemical, development bymost developing agents. The rate of development by hydroquinone (See Figure 133), forexample, appears to be relatively independent of the area of the silver surface and instead to begoverned by the extent of the silver-silver halide interface.The exact mechanisms by which a developing agent acts are relatively complicated, andresearch on the subject is very active.The broad outlines, however, are relatively clear. A molecule of a developing agent can easilygive an electron to an exposed silver bromide grain (that is, to one that carries a latent image),but not to an unexposed grain. This electron can combine with a silver (Ag+) ion of the crystal,neutralizing the positive charge and producing an atom of silver. The process can be repeatedmany times until all the billions of silver ions in a photographic grain have been turned intometallic silver.The development process has both similarities to, and differences from, the process of latentimageformation. Both involve the union of a silver ion and an electron to produce an atom ofmetallic silver. In latent image formation, the electron is freed by the action of radiation andRadiography in Modern Industry 207
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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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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
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
Page 205: electrons by successive Compton int
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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