Radiography in Modern Industry - Kodak

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Chapter 3: Geometric PrinciplesA radiograph is a shadow picture of an object that has been placed in the path of an x-ray orgamma-ray beam, between the tube anode and the film or between the source of gammaradiation and the film. It naturally follows, therefore, that the appearance of an image thusrecorded is materially influenced by the relative positions of the object and the film and by thedirection of the beam. For these reasons, familiarity with the elementary principles of shadowformation is important to those making and interpreting radiographs.General PrinciplesSince x-rays and gamma rays obey the common laws of light, their shadow formation may beexplained in a simple manner in terms of light. It should be borne in mind that the analogybetween light and these radiations is not perfect since all objects are, to a greater or lesserdegree, transparent to x-rays and gamma rays and since scattering presents greater problems inradiography than in optics. However, the same geometric laws of shadow formation hold for bothlight and penetrating radiation.Suppose, as in Figure 11A below, that there is light from a point L falling on a white card C, andthat an opaque object O is interposed between the light source and the card. A shadow of theobject will be formed on the surface of the card.This shadow cast by the object will naturally show some enlargement because the object is not incontact with the card; the degree of enlargement will vary according to the relative distances ofthe object from the card and from the light source. The law governing the size of the shadow maybe stated:The diameter of the object is to the diameter of the shadow as the distance of the light from theobject is to the distance of the light from the card.Mathematically, the degree of enlargement may be calculated by use of the following equations:where S O is the size of the object; S i is the size of the shadow (or the radiographic image); D thedistance from source of radiation to object; and D the distance from the source of radiation to therecording surface (or radiographic film).The degree of sharpness of any shadow depends on the size of the source of light and on theposition of the object between the light and the card--whether nearer to or farther from one or theother. When the source of light is not a point but a small area, the shadows cast are not perfectlysharp (in Figure 11, B to D) because each point in the source of light casts its own shadow of theobject, and each of these overlapping shadows is slightly displaced from the others, producing anill-defined image.The form of the shadow may also differ according to the angle that the object makes with theincident light rays. Deviations from the true shape of the object as exhibited in its shadow imageare referred to as distortion.Figure 11, A to F shows the effect of changing the size of the source and of changing the relativepositions of source, object, and card. From an examination of these drawings, it will be seen thatthe following conditions must be fulfilled to produce the sharpest, truest shadow of the object:
1. The source of light should be small, that is, as nearly a point as can be obtained.Compare Figure 11, A and C.2. The source of light should be as far from the object as practical. Compare Figure 11, Band C.3. The recording surface should be as close to the object as possible. Compare Figure 11,B and D.4. The light rays should be directed perpendicularly to the recording surface. See Figure 11,A and E.5. The plane of the object and the plane of the recording surface should be parallel.Compare Figure 11, A and F.Figure 11: Illustrating the general geometric principles of shadow formation as explainedin these sections.Radiography in Modern Industry 21
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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: Table III - Industrial Gamma-Ray So
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 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
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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
Page 105 and 106:
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
Page 111 and 112:
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
Page 179 and 180:
Since this formula applies only to
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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
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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
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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Radiography in Modern Industry - Kodak

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