Radiography in Modern Industry - Kodak

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Chapter 7: Arithmetic of ExposureRelations Of Milliamperage (Source Strength), Distance, And TimeWith a given kilovoltage of x-radiation or with the gamma radiation from a particular isotope, thethree factors governing the exposure are the milliamperage (for x-rays) or source strength (forgamma rays), time, and source-film distance. The numerical relations among these threequantities are demonstrated below, using x-rays as an example. The same relations apply forgamma rays, provided the number of curies in the source is substituted wherever milliamperageappears in an equation.The necessary calculations for any changes in focus-film distance (D), milliamperage (M), or time(T) are matters of simple arithmetic and are illustrated in the following example. As noted earlier,kilovoltage changes cannot be calculated directly but must be obtained from the exposure chartof the equipment or the operator's logbook.All of the equations shown on these pages can be solved easily for any of the variables (mA, T,D), using one basic rule of mathematics: If one factor is moved across the equals sign (=), itmoves from the numerator to the denominator or vice versa.We can now solve for any unknown by:1. Eliminating any factor that remains constant (has the same value and is in the samelocation on both sides of the equation).2. Simplifying the equation by moving the unknown value so that it is alone on one side ofthe equation in the numerator.3. Substituting the known values and solving the equation.Milliamperage-Distance RelationThe milliamperage employed in any exposure technique should be in conformity with themanufacturer's rating of the x-ray tube. In most laboratories, however, a constant value ofmilliamperage is usually adopted for convenience.Rule: The milliamperage (M) required for a given exposure is directly proportional to the squareof the focus-film distance (D). The equation is expressed as follows:
Example: Suppose that with a given exposure time and kilovoltage, a properly exposedradiograph is obtained with 5mA (M 1 ) at a distance of 12 inches (D 1 ), and that it is desired toincrease the sharpness of detail in the image by increasing the focus-film distance to 24 inches(D 2 ). The correct milliamperage (M 2 ) to obtain the desired radiographic density at the increaseddistance (D 2 ) may be computed from the proportion:When very low kilovoltages, say 20 kV or less, are used, the x-ray intensity decreases withdistance more rapidly than calculations based on the inverse square law would indicate becauseof absorption of the x-rays by the air. Most industrial radiography, however, is done with radiationso penetrating that the air absorption need not be considered. These comments also apply to thetime-distance relations discussed below.Time-Distance RelationRule: The exposure time (T) required for a given exposure is directly proportional to the square ofthe focus-film distance (D). Thus:To solve for either a new Time (T 2 ) Or a new Distance (D 2 ), simply follow the steps shown in theexample above.Tabular Solution of Milliamperage-Time and Distance ProblemsProblems of the types discussed above may also be solved by the use of a table similar to TableV. The factor between the new and the old exposure time, milliamperage, or milliamperageminute(mA-min) value appears in the box at the intersection of the column for the new sourcefilmdistance and the row for the old source-film distance.Suppose, for example, a properly exposed radiograph has an exposure of 20 mA-min with asource-film distance of 30 inches and you want to increase the source-film distance to 45 inchesin order to decrease the geometric unsharpness in the radiograph. The factor appearing in thebox at the intersection of the column for 45 inches (new source-film distance) and the row for 30inches (old source-film distance) is 2.3. Multiply the old milliampere-minute value (20) by 2.3 togive the new value--46 mA-min.Note that some approximation is involved in the use of such a table, since the values in the boxesare rounded off to two significant figures. However, the errors involved are always less than 5percent and, in general, are insignificant in actual practice.Further, a table like Table V obviously cannot include all source-film distances, because oflimitations of space. However, in any one radiographic department, only a few source-filmdistances are used in the great bulk of the work, and a table of reasonable size can beconstructed involving only these few distances.Milliamperage-Time RelationRule: The milliamperage (M) required for a given exposure is inversely proportional to the time(T):Another way of expressing this is to say that for a given set of conditions (voltage, distance, etc),the product of milliamperage and time is constant for the same photographic effect.Radiography in Modern Industry 61
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RadiographyinModernIndustry
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RadiographyinModernIndustryFOURTH E
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ContentsIntroduction...............
Page 7 and 8:
Chapter 1: The Radiographic Process
Page 9 and 10: Intensifying ScreensX-ray and other
Page 11 and 12: makes it a very suitable material f
Page 13 and 14: 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: 0.010-inch front screen of value be
Page 63 and 64: If the milliamperage remains consta
Page 65 and 66: espectively. In other words, a cons
Page 67 and 68: Any given exposure chart applies to
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
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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
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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
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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
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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
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Development is essentially a chemic
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Chapter 19: ProtectionOne of the mo
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duct is brought into the x-ray room
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