Radiography in Modern Industry - Kodak

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Chapter 4: Factors Governing ExposureGenerally speaking, the density of any radiographic image depends on the amount of radiationabsorbed by the sensitive emulsion of the film. This amount of radiation in turn depends onseveral factors: the total amount of radiation emitted by the x-ray tube or gamma-ray source; theamount of radiation reaching the specimen; the proportion of this radiation that passes throughthe specimen; and the intensifying action of the screens, if they are used. This chapter discussesthe effects of these factors.Radiation Emitted By SourceX-raysThe total amount of radiation emitted by an x-ray tube depends on tube current (milliamperage),kilovoltage, and the time the tube is energized.When other operating conditions are held constant, a change in milliamperage causes a changein the intensity of the radiation emitted, the intensity being approximately proportional to themilliamperage. The high voltage transformer saturation and voltage waveform can change withtube current, but a compensation factor is usually applied to minimize the effects of thesechanges. In normal industrial radiographic practice, the variation from exact proportionality is notserious and may usually be ignored.Figure 18 shows spectral emission curves for an x-ray tube operated at two different currents, thehigher being twice the lower. Therefore, each wavelength is twice as intense in one beam as inthe other. Note that no wavelengths are present in one beam that are not present in the other.Hence, there is no change in x-ray quality or penetrating power.As would be expected, the total amount of radiation emitted by an x-ray tube operating at acertain kilovoltage and milliamperage is directly proportional to the time the tube is energized.Figure 18: Curves illustrating the effect of a change in milliamperage on the intensity of anx-ray beam. (After Ulrey.)Since the x-ray output is directly proportional to both milliamperage and time, it is directlyproportional to their product. (This product is often referred to as the "exposure".) Algebraically,this may be stated E = Mt, where E is the exposure, M the tube current, and t the exposure time.Hence, the amount of radiation will remain constant if the exposure remains constant, no matterhow the individual factors of tube current and exposure time are varied. This permits specifying x-ray exposures in terms of milliampere-minutes or milliampere-seconds, without stating thespecific individual values of tube current and time.
The kilovoltage applied to the x-ray tube affects not only the quality but also the intensity of thebeam. As the kilovoltage is raised, x-rays of shorter wavelength, and hence of more penetratingpower, are produced. Figure 19 shows spectral emission curves for an x-ray tube operated at twodifferent kilovoltages but at the same milliamperage. Note that, in the higher-kilovoltage beam,there are some shorter wavelengths that are absent from the lower-kilovoltage beam. Further, allwavelengths present in the lower-kilovoltage beam are present in the more penetrating beam,and in greater amount. Thus, raising the kilovoltage increases both the penetration and theintensity of the radiation emitted from the tube.Figure 19: Curves illustrating the effect of a change in kilovoltage on the composition andintensity of an x-ray beam. (After Ulrey.)Gamma RaysThe total amount of radiation emitted from a gamma-ray source during a radiographic exposuredepends on the activity of the source (usually stated in curies) and the time of exposure. For aparticular radioactive isotope, the intensity of the radiation is approximately proportional to theactivity (in curies) of the source. If it were not for absorption of gamma rays within the radioactivematerial itself (see the discussion on self-absorption in "Gamma-Ray Sources") thisproportionality would be exact. In normal radiographic practice, the range of source sizes used ina particular location is small enough so that variations from exact proportionality are not seriousand may usually be ignored.Thus, the gamma-ray output is directly proportional to both activity of the source and time, andhence is directly proportional to their product. Analogously to the x-ray exposure, the gamma-rayexposure E may be stated E = Mt, where M is the source activity in curies and t is the exposuretime, the amount of gamma radiation remaining constant so long as the product of source activityand time remains constant. This permits specifying gamma-ray exposures in curie-hours withoutstating specific values for source activity or time.Since gamma-ray energy is fixed by the nature of the particular radioactive isotope, there is novariable to correspond to the kilovoltage factor encountered in x-radiography. The only way tochange penetrating power when using gamma rays is to change the source, i.e., cobalt 60 inplace of iridium 192 (see Figure 8).Inverse Square LawWhen the x-ray tube output is held constant, or when a particular radioactive source is used, theradiation intensity reaching the specimen is governed by the distance between the tube (orsource) and the specimen, varying inversely with the square of this distance. The explanation thatfollows is in terms of x-rays and light, but it applies to gamma rays as well.Radiography in Modern Industry 29
Page 1 and 2: RadiographyinModernIndustry
Page 3 and 4: RadiographyinModernIndustryFOURTH E
Page 5 and 6: 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: Figure 17: Pinhole pictures of the
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 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
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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
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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
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
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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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Radiography in Modern Industry - Kodak

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