Radiography in Modern Industry - Kodak

More documents

Recommendations

Info

The quality of the radiation necessary to obtain an appreciable intensification from lead foilscreens depends on the type of film, the kilovoltage, and the thickness of the material throughwhich the rays must pass. (See Figure 25) In the radiography of aluminum, for example, using a0.005-inch front screen and a 0.010-inch back screen, the thickness of aluminum must be about 6inches and the kilovoltage as high as 160 kV to secure any advantage in exposure time with leadscreens. In the radiography of steel, lead screens begin to give appreciable intensification withthicknesses in the neighborhood of 1/4 inch, at voltages of 130 to 150 kV. In the radiography of11/4 inches of steel at about 200 kV, lead screens permit an exposure of about one third of thatwithout screens (intensification factor of 3). With cobalt 60 gamma rays, the intensification factorof lead screens is about 2. Lead foil screens, however, do not detrimentally affect the definition orgraininess of the radiographic image to any material degree so long as the lead and the film arein intimate contact.Figure 26: Upper area shows decreased density caused by paper between the lead screenand film. An electron shadow picture of the paper structure has also been introduced.Lead foil screens diminish the effect of scattered radiation, particularly that which undercuts theobject (See "Scattered Radiation"), when the primary rays strike the portions of the film holder orcassette outside the area covered by the object.Scattered radiation from the specimen itself is cut almost in half by lead screens, contributing tomaximum clarity of detail in the radiograph; this advantage is obtained even under conditionswhere the lead screen makes necessary an increase in exposure. A more exhaustive discussionof scattered radiation will be found in "Scattered Radiation".In radiography with gamma rays or high-voltage x-rays, films loaded in metal cassettes withoutscreens are likely to record the effect of secondary electrons generated in the lead-covered backof the cassette. These electrons, passing through the felt pad on the cassette cover, produce amottled appearance because of the structure of the felt. Films loaded in the customary leadbackedcardboard exposure holder may also show a pattern of the structure of the paper that liesbetween the lead and the film (See Figure 26.). To avoid these effects, film should be enclosedbetween double lead screens, care being taken to ensure good contact between film andscreens. Thus, lead foil screens are essential in practically all radiography with gamma rays ormillion-volt x-rays. If, for any reason, screens cannot be used with these radiations, use alightproof paper or cardboard holder with no metal backing.Radiography in Modern Industry 40
Contact between the film and the lead foil screens is essential to good radiographic quality. Areasin which contact is lacking produce "fuzzy" images, as shown in (See Figure 27).Figure 27: Good contact between film and lead foil screens gives a sharp image (left).Poor contact results in a fuzzy image (right).Selection and Care of Lead ScreensLead foil for screens must be selected with extreme care. Commercially pure lead is satisfactory.An alloy of 6 percent antimony and 94 percent lead, being harder and stiffer, has betterresistance to wear and abrasion. Avoid tin-coated lead foil, since irregularities in the tin cause avariation in the intensifying factor of the screens, resulting in mottled radiographs. Minorblemishes do not affect the usefulness of the screen, but large "blisters" or cavities should beavoided.Most of the intensifying action of a lead foil screen is caused by the electrons emitted under x-rayor gamma-ray excitation. Because electrons are readily absorbed even in thin or light materials,the surface must be kept free of grease and lint which will produce light marks on the radiograph.Small flakes of foreign material--for example, dandruff or tobacco--will likewise produce lightspots on the completed radiograph. For this same reason, protective coatings on lead foil screensare not common. Any protective coating should be thin, to minimize the absorption of electronsand keep the intensification factors as high as possible, and uniform so that the intensificationfactor will be uniform. (In addition, the coating should not produce static electricity when rubbedagainst or placed in contact with film--See Figure 28.)Radiography in Modern Industry 41
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 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: Chapter 5: Radiographic ScreensWhen
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
Page 79 and 80: Figure 56: Transparent overlay posi
Page 81 and 82: Figure 58: Overlay positioned so as
Page 83 and 84: The problem of radiographing a part
Page 85 and 86: Figure 62: System of lines drawn on
Page 87 and 88: Chapter 8: Radiographic Image Quali
Page 89 and 90: Film contrast refers to the slope (
Page 91 and 92:
Hole Type PenetrametersThe common p
Page 93 and 94:
of the same thickness as the specim
Page 95 and 96:
Chapter 9: Industrial X-ray FilmsMo
Page 97 and 98:
Figure 70 indicates the direction t
Page 99 and 100:
the lead letters on a radiation-abs
Page 101 and 102:
Therefore, protection requirements
Page 103 and 104:
5. Avoid pressure damage caused by
Page 105 and 106:
Paddles or plunger-type agitators a
Page 107 and 108:
slow, and the development time reco
Page 109 and 110:
ubbles make their way to the surfac
Page 111 and 112:
When development is complete, the f
Page 113 and 114:
soften considerably with prolonged
Page 115 and 116:
Figure 77: The roller transport sys
Page 117 and 118:
Rapid Access to Processed Radiograp
Page 119 and 120:
Figure 78: Film-feeding procedures
Page 121 and 122:
Chapter 11: Process ControlUsers of
Page 123 and 124:
3. Age of the developer replenisher
Page 125 and 126:
Figure 80: Control chart below for
Page 127 and 128:
DiscussionDensitometric data and pr
Page 129 and 130:
Figure 82: Plan of a manual x-ray p
Page 131 and 132:
Figure 83: A schematic diagram of a
Page 133 and 134:
loading-bench activities are carrie
Page 135 and 136:
KODAK Quinone-Thiosulfate Intensifi
Page 137 and 138:
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 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 and 210:
Chapter 19: ProtectionOne of the mo
Page 211 and 212:
duct is brought into the x-ray room
show all

Radiography in Modern Industry - Kodak

Create successful ePaper yourself

Delete template?

Save as template?