Radiography in Modern Industry - Kodak

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possible. Where only scattered radiation can reach a protective wall, less protection is necessary,since the intensity of the scattered radiation is much lower than that of the primary. Whenadvantage is taken of these economies, great care must be exercised in rearranging equipment,lest it become possible to direct the full intensity of the x-ray beam against a wall that containsprotection against the scattered radiation only.Where large numbers of relatively small parts are inspected, the protection may be in a morecompact form such as a lead-lined hood surrounding the x-ray tube, the specimens, and the filmholder, completely enclosing them for the duration of the exposure. When the exposure iscompleted, the hood is opened to allow the removal of the radiographed parts and the placementof a new batch. The electrical controls are interlocked so that the x-ray tube cannot be turned onuntil the hood is closed.The protective material, usually lead, in the walls of the enclosure, whether it be a room or acabinet, should be of sufficient thickness to reduce the exposure in all occupied areas to thelowest value possible or economically feasible. Under no circumstances should the exposure topersonnel exceed that permitted by the pertinent regulations, and a lower level than this shouldbe sought whenever possible.In some cases, it may be possible for the personnel of an x-ray department, or other employees,to be exposed to the radiation from more than one x-ray machine. In such cases, the amount ofprotection must be increased to a point where the total exposure in any occupied area is withinthe prescribed radiation limits.If the object being radiographed is too large or heavy to be brought to the x-ray machine, theradiography must be done in the shop. Under such conditions, special precautions are necessary.These include a completely lead-lined booth large enough to accommodate the x-ray machinecontrols, the operator, and his assistants. The booth may be completely enclosed, or open on oneside. In any event, the exposure within it should be very carefully measured. Lead cones on the x-ray machine should be used to confine the x-ray beam to a certain direction and to the minimumangle that can be used. Portable screens should be provided to protect workers nearby. Guardrails or ropes and warnings should be used to keep others at a safe distance.In field radiography, protection is usually obtained by distance. Care should be taken to see thatall personnel are far enough away from the radiation source to insure safety.Material And Construction For Protection Against X-RaysLead is the most common material used to provide protection against x-rays. It combines highprotective efficiency with low cost and easy availability. In most cases, recommendations onprotective measures are given in terms of lead thicknesses.When using lead for protection, care must be taken to avoid any leaks in the shielding. Thismeans that adjacent lead sheets should be over-lapped, not merely butted, even if the sheets areto be burned together throughout the whole length of the joint. The heads of any nails or screwsthat pass through the lead should be carefully covered with lead. Extra precautions should betaken at those points where water pipes, electrical conduits, or ventilating ducts pass through thewalls of the x-ray room. For small conduits and pipes, it is usually sufficient to provide a leadsheathing around the pipe for some distance on one side of the lead protective barrier in the wall.This sheath should be continuous and be very carefully joined, by a burned joint, to the lead inthe wall. Better protection is afforded by having a right-angle bend in the pipe either inside oroutside the x-ray room and covering it with a lead sheath to a point well beyond the right-anglebend. The sheath should be carefully joined to the lead in the wall. In the case of a large openingfor ventilation, lead baffles will stop x-rays, but permit the passage of air. When a large ventilatingRadiography in Modern Industry 210
duct is brought into the x-ray room, two right-angled bends covered with lead will prevent theescape of x-rays.If the x-ray room is on the lowest floor of a building, the floor of the room need not be completelyprotected. The lead protection in the wall should not stop at the floor level, however. An "apron" oflead, continuous with the protection within the wall, should be placed in the floor, extendinginward from all four walls. The purpose of this apron is to prevent x-rays from escaping from theroom by penetrating the floor and then scattering upward outside the protective barrier. Analternative is to extend the lead protection in the walls downward for some distance below floorlevel. The same considerations apply to the ceiling if the x-ray room is located on the top floor ofa building. Of course, if there is occupied space above or below the x-ray room, the ceiling ordoor of the x-ray room must have full radiation protection over its whole area.Although lead is the most common material for x-ray protection, other materials may be used. Inparticular, structural walls of concrete or brick may afford considerable protection and may reducethe thickness, and therefore the cost, of the lead required. Above 400 kV, concrete is most usedas protective material. The thicknesses of lead required at these potentials are so great thatfastening the lead to the walls becomes a serious problem, and concrete is often used because ofthe ease of construction. In new construction, the use of concrete may have economicadvantages even for protection against radiations generated at kilovoltages well below 400. Stateand local codes should be examined, and any installations checked for compliance with theirrequirements.Protection Against Gamma RaysMost gamma-ray emitters used in industry are artificial radioactive isotopes; the procurement,use, handling, storage, and the like are controlled directly by the United States Atomic EnergyCommission, or indirectly by state radiation control laws approved by the Atomic EnergyCommission. It is essential, therefore, that these codes be followed rigorously.Gamma rays may be very penetrating. For instance, one-half inch of lead reduces the intensity ofthe gamma rays of cobalt 60 only about 50 percent. This makes the problems of protectionsomewhat different from those encountered in protection against moderate-voltage x-rays ingeneral, it is not feasible to provide safety from gamma rays solely by means of a protectivebarrier. Therefore, distance or a combination of distance and protective material is usuallyrequired. When radioactive materials are not in use, protection is usually obtained by keepingthem in thick lead containers, because in this case the total amount of lead needed is not great.Because of the great thicknesses of protective materials required for shielding some gamma-raysources, distance is the most economical method of protection while the source is in use. Adanger zone should be roped off around the location of the radioactive material, and personnelshould be forbidden to enter this zone except to put the source in position or return it to its safe.Suitable conspicuous signs should be provided to warn away the casual passersby. Tables areavailable that give data for calculating the distances from various amounts of radioactive materialat which a radiation hazard exists.It must be kept in mind that the presence of a large mass of scattering material, for example, awall, will materially increase the gamma-ray exposure. This increase may be as much as 50percent of the exposure as calculated without the presence of scattering material. Thus, to besure that the radiation protection is adequate, factors other than distance must be kept in mindwhen considering personnel protection from gamma rays.Precautions must be taken in shipping radioactive materials, not only to protect those who handlethem in transit but also to prevent the fogging of photographic materials that may be transportedin the same vehicle. The Interstate Commerce Commission has established regulationsRadiography in Modern Industry 211
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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
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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
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 and 190: Density = 1.5 Density = 2.5Film Rel
Page 191 and 192: In most industrial radiography, the
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: Chapter 19: ProtectionOne of the mo
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