Radiography in Modern Industry - Kodak

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used and on the processing conditions. The linear relation between density and exposure may beextremely useful, for instance, in the interpretation of diffraction patterns and the evaluation ofradiation monitoring films, provided it is kept in mind that the linear range of the curve is limited.Reciprocity Law FailureThe Bunsen-Roscoe reciprocity law states that the resultant of a photochemical reaction isdependent only on the product (I x t) of the radiation intensity (I) and the duration of the exposure(t), and is independent of the absolute values of either quantity. Applied to radiography, thismeans that the developed density in a film depends only on the product of x- or gamma-rayintensity reaching the film and the time of exposure.The reciprocity law is valid for direct x-ray or gamma-ray exposures, or those made with lead foilscreens, over a range of radiation intensities and exposure times much greater than thosenormally used in practice. It fails, however, for exposures to light and, therefore, for exposuresusing fluorescent intensifying screens. The magnitude of the differences that may be expected inpractice are shown in an earlier table. Figure 120 shows a conventional reciprocity curve. (Thedata in the table were derived from a curve of this type.) The vertical axis in Figure 120 has beenconsiderably expanded to make the curvature more apparent.Figure 120: Reciprocity curve for light exposures. The corresponding curve for direct x-rays or lead screen exposures would be a straight line parallel to the log I axis.The logarithms of the exposures (I x t) that produce a given density are plotted against thelogarithms of the individual intensities. It can be seen that for a particular intensity (I O) theexposure (I x t) O required to produce the given density is a minimum. It is for this intensity of lightthat the film is most efficient in its response. For light intensities higher (I H) and lower (I L) than I O,the exposure required to produce the given density is greater than (I x t) O. Phrased differently,there is a certain intensity of light for which a particular film is most efficient in its response. Inradiography with fluorescent screens, failure of the reciprocity law sometimes gives results thatappear to be a failure of the inverse square law (See Table VI).Radiography in Modern Industry 190
In most industrial radiography, the brightness of fluorescent intensifying screens is very low, andthe exposures used lie on the left-hand branch of the curve shown in Figure 120. An exception ishigh-speed flash radiography in which the exposures lie to the right of the minimum.See also "The Reciprocity Law".Effect Of Development Time On Speed And ContrastAlthough the shape of the characteristic curve is relatively insensitive to changes in x- or gammarayquality, it is affected by changes in degree of development. Degree of development, in turn,depends on the type of developer, its temperature, its degree of activity, and the time ofdevelopment. Within certain limits, increased degree of development increases the speed andcontrast of an x-ray film. If, however, development is carried too far, the speed of the film asbased on a certain net density (density above base density and fog) ceases to increase and mayeven decrease. The fog increases and contrast may decrease.Automated ProcessingAutomated processors and their associated chemicals are designed to give the optimum degreeof development. All the variables, listed in the above paragraph, that affect the degree ofdevelopment are controlled and kept constant by the processor. The responsibilities of theoperator are to keep the machine clean and to make sure that temperatures, replenishment rates,and the like are maintained at the proper levels.Manual ProcessingIn manual processing, however, all the processing variables are under the control of the operator.Although all are important in the production of the final radiograph, those associated withdevelopment are particularly so. The following discussion is therefore devoted to the effects ofdevelopment variables, in the context of manual processing.Figure 121 shows the characteristic curves of a typical industrial x-ray film developed for a seriesof times in developer at 68°F. It can be seen that as development time increases, thecharacteristic curve grows progressively steeper (contrast increasing) and moves progressively tothe left (speed increasing). Note that the curves for 2 and 10 minutes represent developmenttechniques that would never be encountered in practice. They are included here merely asextreme examples.Radiography in Modern Industry 191
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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
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Table I - Typical X-ray Machines an
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The wavelengths (or energies of rad
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Table III - Industrial Gamma-Ray So
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1. The source of light should be sm
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B and H in the Figure 13 show the e
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Figure 14: Geometric construction f
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Figure 17: Pinhole pictures of the
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The kilovoltage applied to the x-ra
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Figure 21: Schematic diagram of som
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kind of material radiographed, the
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instance, the kilovoltage may be fi
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The technique need not be limited t
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Chapter 5: Radiographic ScreensWhen
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Contact between the film and the le
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Figure 29: The number of electrons
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lead foil screens ran be retained w
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Figure 33: The sharpness of the rad
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Figure 34: Low density (right) is a
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such as a wall or floor, on the fil
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from this source. Since scatter als
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A filter reduces excessive subject
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Definite rules as to filter thickne
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0.010-inch front screen of value be
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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
Page 139 and 140: KODAK Hypo Test Solution HT-2Avoird
Page 141 and 142: In summary, use of the test papers
Page 143 and 144: narrow angle would be very thick, e
Page 145 and 146: When radiation passes through a spe
Page 147 and 148: Figure 89: Demonstration of the eff
Page 149 and 150: Figure 90: The amount of gamma radi
Page 151 and 152: The radiograph exposed in the right
Page 153 and 154: To illustrate, let us assume that t
Page 155 and 156: Figure 95: High-speed x-ray picture
Page 157 and 158: Figure 97: Two methods of neutron r
Page 159 and 160: Duplicating RadiographsSimultaneous
Page 161 and 162: Sometimes, as when sets of referenc
Page 163 and 164: PhotofluorographyIn photofluorograp
Page 165 and 166: discontinuities or of segregation i
Page 167 and 168: from the camera or by reaching down
Page 169 and 170: Figure 106: Schematic diagram of th
Page 171 and 172: valuable technique, for instance, i
Page 173 and 174: The position of the spots is determ
Page 175 and 176: Powder Diffraction File, Internatio
Page 177 and 178: Processing TechniquesRadiographs on
Page 179 and 180: Since this formula applies only to
Page 181 and 182: 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
Page 187 and 188: film fairly well. If high densities
Page 189: Density = 1.5 Density = 2.5Film Rel
Page 193 and 194: e noted here. Although the average
Page 195 and 196: Chapter 17: Film Graininess; Signal
Page 197 and 198: The ratio of signal to noise has a
Page 199 and 200: Chapter 18: The Photographic Latent
Page 201 and 202: Thus, the change that makes an expo
Page 203 and 204: Figure 130: Stages in the developme
Page 205 and 206: electrons by successive Compton int
Page 207 and 208: 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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