Radiography in Modern Industry - Kodak

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Figure 44: Typical exposure chart for steel. This chart may be taken to apply to Film X (forexample), with lead foil screens, at a film density of 1.5. Source-film distance, 40 inches.Exposure charts are usually available from manufacturers of x-ray equipment. Because, ingeneral, such charts cannot be used for different x-ray machines unless suitable correctionfactors are applied, individual laboratories sometimes prepare their own.Preparing An Exposure ChartA simple method for preparing an exposure chart is to make a series of radiographs of a pile ofplates consisting of a number of steps. This "step tablet" or stepped wedge, is radiographed atseveral different exposure times at each of a number of kilovoltages. The exposed films are allprocessed under conditions identical to those that will later be used for routine work. Eachradiograph consists of a series of photographic densities corresponding to the x-ray intensitiestransmitted by the different thicknesses of metal. A certain density, for example, 1.5, is selectedas the basis for the preparation of the chart. Wherever this density occurs on the stepped-wedgeradiographs, there are corresponding values of thickness, milliampere-minutes, and kilovoltage. Itis unlikely that many of the radiographs will contain a value of exactly 1.5 in density, but thecorrect thickness for this density can be found by interpolation between steps. Thickness andmilliampere-minute values are plotted for the different kilovoltages in the manner shown in Figure44.Another method, requiring fewer stepped wedge exposures but more arithmetical manipulation, isto make one step-tablet exposure at each kilovoltage and to measure the densities in theprocessed stepped-wedge radiographs. The exposure that would have given the chosen density(in this case 1.5) under any particular thickness of the stepped wedge can then be determinedfrom the characteristic curve of the film used (See "The Characteristic Curve"). The values forthickness, kilovoltage, and exposure are plotted as described in the figure above.Note that thickness is on a linear scale, and that milliampere-minutes are on a logarithmic scale.The logarithmic scale is not necessary, but it is very convenient because it compresses anotherwise long scale. A further advantage of the logarithmic exposure scale is that it usuallyallows the location of the points for any one kilovoltage to be well approximated by a straight line.Radiography in Modern Industry 66
Any given exposure chart applies to a set of specific conditions. These fixed conditions are:1. The x-ray machine used2. A certain source-film distance3. A particular film type4. Processing conditions used5. The film density on which the chart is based6. The type of screens (if any) that are usedOnly if the conditions used in making the radiograph agree in all particulars with those used inpreparation of the exposure chart can values of exposure be read directly from the chart. Anychange requires the application of a correction factor. The correction factor applying to each ofthe conditions listed previously will be discussed separately.1. It is sometimes difficult to find a correction factor to make an exposure chart prepared forone x-ray machine applicable to another. Different x-ray machines operating at the samenominal kilovoltage and milliamperage settings may give not only different intensities butalso different qualities of radiation.2. A change in source-film distance may be compensated for by the use of the inversesquare law or, if fluorescent screens are used, by referring to the earlier table. Someexposure charts give exposures in terms of "exposure factor" rather than in terms ofmilliampere-minutes or milliampere-seconds. Charts of this type are readily applied toany value of source-film distance.3. The use of a different type of film can be corrected for by comparing the difference in theamount of exposure necessary to give the same density on both films from relativeexposure charts such as those shown in Figure 47.• For example, to obtain a density of 1.5 using Film Y, 0.6 more exposure isrequired than for Film X.• This log exposure difference is found on the L scale and corresponds to anexposure factor of 3.99 on the D scale. (Read directly below the log Edifference.) Therefore, in order to obtain the same density on Film Y as onFilm X, multiply the original exposure by 3.99 to get the new exposure.Conversely, if going from Film Y to Film X, divide the original exposure by3.99 to obtain the new exposure.• You can use these procedures to change densities on a single film as well.Simply find the log E difference needed to obtain the new density on the filmcurve; read the corresponding exposure factor from the chart; then multiply toincrease density or divide to decrease density.4. A change in processing conditions causes a change in effective film speed. If theprocessing of the radiographs differs from that used for the exposures from which thechart was made, the correction factor must be found by experiment.5. The chart gives exposures to produce a certain density. If a different density is required,the correction factor may be calculated from the film's characteristic curve (See "TheCharacteristic Curve").6. If the type of screens is changed, for example from lead foil to fluorescent, it is easier andmore accurate to make a new exposure chart than to attempt to determine correctionfactors.Sliding scales can be applied to exposure charts to allow for changes in one or more of theconditions discussed, with the exception of the first and the last. The methods of preparing andusing such scales are described in detail later on.In some radiographic operations, the exposure time and the source-film distance are set byeconomic considerations or on the basis of previous experience and test radiographs. The tubecurrent is, of course, limited by the design of the tube. This leaves as variables only the thicknessRadiography in Modern Industry 67
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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
Page 15 and 16: Table I - Typical X-ray Machines an
Page 17 and 18: The wavelengths (or energies of rad
Page 19 and 20: Table III - Industrial Gamma-Ray So
Page 21 and 22: 1. The source of light should be sm
Page 23 and 24: B and H in the Figure 13 show the e
Page 25 and 26: Figure 14: Geometric construction f
Page 27 and 28: Figure 17: Pinhole pictures of the
Page 29 and 30: The kilovoltage applied to the x-ra
Page 31 and 32: Figure 21: Schematic diagram of som
Page 33 and 34: kind of material radiographed, the
Page 35 and 36: instance, the kilovoltage may be fi
Page 37 and 38: The technique need not be limited t
Page 39 and 40: Chapter 5: Radiographic ScreensWhen
Page 41 and 42: Contact between the film and the le
Page 43 and 44: Figure 29: The number of electrons
Page 45 and 46: lead foil screens ran be retained w
Page 47 and 48: Figure 33: The sharpness of the rad
Page 49 and 50: Figure 34: Low density (right) is a
Page 51 and 52: such as a wall or floor, on the fil
Page 53 and 54: from this source. Since scatter als
Page 55 and 56: A filter reduces excessive subject
Page 57 and 58: Definite rules as to filter thickne
Page 59 and 60: 0.010-inch front screen of value be
Page 61 and 62: Example: Suppose that with a given
Page 63 and 64: If the milliamperage remains consta
Page 65: espectively. In other words, a cons
Page 69 and 70: Figure 46: Typical gamma-ray exposu
Page 71 and 72: where the slope of the characterist
Page 73 and 74: Figure 49: Characteristic curves of
Page 75 and 76: Figure 51: Characteristic curve of
Page 77 and 78: Nomogram MethodsIn Figure 54, the s
Page 79 and 80: Figure 56: Transparent overlay posi
Page 81 and 82: Figure 58: Overlay positioned so as
Page 83 and 84: The problem of radiographing a part
Page 85 and 86: Figure 62: System of lines drawn on
Page 87 and 88: Chapter 8: Radiographic Image Quali
Page 89 and 90: Film contrast refers to the slope (
Page 91 and 92: Hole Type PenetrametersThe common p
Page 93 and 94: of the same thickness as the specim
Page 95 and 96: Chapter 9: Industrial X-ray FilmsMo
Page 97 and 98: Figure 70 indicates the direction t
Page 99 and 100: the lead letters on a radiation-abs
Page 101 and 102: 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
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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
Page 127 and 128:
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
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Figure 95: High-speed x-ray picture
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Figure 97: Two methods of neutron r
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Duplicating RadiographsSimultaneous
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Sometimes, as when sets of referenc
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PhotofluorographyIn photofluorograp
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discontinuities or of segregation i
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from the camera or by reaching down
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Figure 106: Schematic diagram of th
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valuable technique, for instance, i
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The position of the spots is determ
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Powder Diffraction File, Internatio
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Processing TechniquesRadiographs on
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Since this formula applies only to
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such that it does not distort the i
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Figure 113: A: Representation of a
Page 185 and 186:
Figure 115: Characteristic curve of
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film fairly well. If high densities
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Density = 1.5 Density = 2.5Film Rel
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In most industrial radiography, the
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e noted here. Although the average
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Chapter 17: Film Graininess; Signal
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The ratio of signal to noise has a
Page 199 and 200:
Chapter 18: The Photographic Latent
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Thus, the change that makes an expo
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Figure 130: Stages in the developme
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electrons by successive Compton int
Page 207 and 208:
Development is essentially a chemic
Page 209 and 210:
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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