Radiography in Modern Industry - Kodak

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Chapter 2: X-Ray and Gamma-Ray SourcesProduction of X-RaysX-rays are produced when electrons, traveling at high speed, collide with matter or changedirection. In the usual type of x-ray tube, an incandescent filament supplies the electrons and thusforms the cathode, or negative electrode, of the tube. A high voltage applied to the tube drives theelectrons to the anode, or target. The sudden stopping of these rapidly moving electrons in thesurface of the target results in the generation of x-radiation.The design and spacing of the electrodes and the degree of vacuum are such that no flow ofelectrical charge between cathode and anode is possible until the filament is heated.The X-Ray TubeFigure 4 is a schematic diagram of the essential parts of an x-ray tube. The filament is heated bya current of several amperes from a low-voltage source, generally a small transformer. Thefocusing cup serves to concentrate the stream of electrons on a small area of the target, calledthe focal spot. This stream of electrons constitutes the tube current and is measured inmilliamperes.Figure 4: Schematic diagram of an x-ray tube.The higher the temperature of the filament, the greater is its emission of electrons and the largerthe resulting tube current. The tube current is controlled, therefore, by some device that regulatesthe heating current supplied to the filament. This is usually accomplished by a variable-voltagetransformer, which energizes the primary of the filament transformer. Other conditions remainingthe same, the x-ray output is proportional to the tube current.Most of the energy applied to the tube is transformed into heat at the focal spot, only a smallportion being transformed into x-rays. The high concentration of heat in a small area imposes asevere burden on the materials and design of the anode. The high melting point of tungsten
makes it a very suitable material for the target of an x-ray tube. In addition, the efficiency of thetarget material in the production of x-rays is proportional to its atomic number.1 Since tungstenhas a high atomic number, it has a double advantage. The targets of practically all industrial x-raymachines are made of tungsten.CoolingCirculation of oil in the interior of the anode is an effective method of carrying away the heat.Where this method is not employed, the use of copper for the main body of the anode provideshigh heat conductivity, and radiating fins on the end of the anode outside the tube transfer theheat to the surrounding medium. The focal spot should be as small as conditions permit, in orderto secure the sharpest possible definition in the radiographic image. However, the smaller thefocal spot, the less energy it will withstand without damage. Manufacturers of x-ray tubes furnishdata in the form of charts indicating the kilovoltages and milliamperages that may be safelyapplied at various exposure times. The life of any tube will be shortened considerably if it is notalways operated within the rated capacity.Focal-Spot SizeThe principle of the line focus is used to provide a focal spot of small effective size, though theactual focal area on the anode face may be fairly large, as illustrated figure 5. By making theangle between the anode face and the central ray small, usually 20 degrees, the effective area ofthe spot is only a fraction of its actual area. With the focal area in the form of a long rectangle, theprojected area in the direction of the central ray is square.Figure 5: Diagram of a line-focus tube depicting the relation between actual focal-spotarea (area of bombardment) and effective focal spot, as projected from a 20° anode.Effects of KilovoltageAs will be seen later, different voltages are applied to the x-ray tube to meet the demands ofvarious classes of radiographic work. The higher the voltage, the greater the speed of theelectrons striking the focal spot. The result is a decrease in the wavelength of the x-rays emittedand an increase in their penetrating power and intensity. It is to be noted that x-rays produced, forexample, at 200 kilovolts contain all the wavelengths that would be produced at 100 kilovolts, andwith greater intensity. In addition, the 200-kilovolt x-rays include some shorter wavelengths thatdo not exist in the 100-kilovoIt spectrum at all. The higher voltage x-rays are used for thepenetration of thicker and heavier materials.Most x-ray generating apparatus consists of a filament supply and a high-voltage supply.Radiography in Modern Industry 11
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: Intensifying ScreensX-ray and other
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 and 60: 0.010-inch front screen of value be
Page 61 and 62:
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
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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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Radiography in Modern Industry - Kodak

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