Radiography in Modern Industry - Kodak

More documents

Recommendations

Info

Exposure FactorThe "exposure factor" is a quantity that combines milliamperage (x-rays) or source strength(gamma rays), time, and distance. Numerically the exposure factor equalsRadiographic techniques are sometimes given in terms of kilovoltage and exposure factor, orradioactive isotope and exposure factor. In such a case, it is necessary to multiply the exposurefactor by the square of the distance to be used in order to find, for example, the milliampereminutesor the curie-hours required.Determination Of Exposure FactorsX-raysThe focus-film distance is easy to establish by actual measurement; the milliamperage canconveniently be determined by the milliammeter supplied with the x-ray machine; and theexposure time can be accurately controlled by a good time-switch. The tube voltage, however, isdifficult and inconvenient to measure accurately. Furthermore, designs of individual machinesdiffer widely, and may give x-ray outputs of a different quality and intensity even when operated atthe same nominal values of peak kilovoltage and milliamperage.Consequently, although specified exposure techniques can be duplicated satisfactorily in thefactors of focus-film distance, milliamperage, end exposure time, one apparatus may differmaterially from another in the kilovoltage setting necessary to produce the same radiographicdensity. Because of this, the kilovoltage setting for a given technique should be determined bytrial on each x-ray generator. In the preliminary tests, published exposure charts may be followedas an approximate guide. It is customary for equipment manufacturers to calibrate x-raymachines at the factory and to furnish suitable exposure charts. For the unusual problems thatarise, it is desirable to record in a logbook all the data on exposure and techniques. In this way,operators will soon build up a source of information that will make them more competent to dealwith difficult situations.For developing trial exposures, a standardized technique should always be used. If this is done,any variation in the quality of the trial radiographs may then be attributed to the exposure alone.This method obviates many of the variable factors common to radiographic work.Since an increase of kilovoltage produces a marked increase in x-ray output and penetration (SeeFigure 19), it is necessary to maintain a close control of this factor in order to secure radiographsof uniform density. In many types of industrial radiography where it is desirable to maintainconstant exposure conditions with regard to focus-film distance, milliamperage, and exposuretime, it is common practice to vary the kilovoltage in accordance with the thickness of the materialto be examined so as to secure proper density in the radiographic image. Suppose, for example,it is desired to change from radiographing 11/2-inch steel to radiographing 2-inch steel. The 2-inch steel will require more than 10 times the exposure in milliampere-minutes at 170 kilovolts.However, increasing the kilovoltage to a little more than 200 will yield a comparable radiographwith the same milliampere-minutes Thus, kilovoltage is an important variable because economicconsiderations often require that exposure times be kept within fairly narrow limits. It is desirable,as a rule, to use as low a kilvoltage as other factors will permit. In the case of certain high-voltagex-ray machines, the technique of choosing exposure conditions may be somewhat modified. ForRadiography in Modern Industry 34
instance, the kilovoltage may be fixed rather than adjustable at the will of the operator, leavingonly milliamperage, exposure time, film type, and focus-film distance as variables.Gamma RaysWith radioactive materials, the variable factors are more limited than with x-rays. Not only is thequality of the radiation fixed by the nature of the emitter, but also the intensity is fixed by theamount of radioactive material in the particular source. The only variables under the control ofoperators, and the only quantities they need to determine, are the source-fiim distance, film type,and the exposure time. As in the case of x-radiography, it is desirable to develop trial exposuresusing the gamma-ray sources under standardized conditions and to record all data on exposuresand techniques.ContrastIn a radiograph, the various intensities transmitted by the specimen are rendered as differentdensities in the image. The density differences from one area to another constitute radiographiccontrast. Any shadow or detail within the image is visible by reason of the contrast between it andits background of surrounding structures. Within appropriate limits, the greater the contrast ordensity differences in the radiograph, the more definitely various details will stand out. However, ifoverall contrast is increased too much, there is an actual loss in visibility of detail in both the thickand the thin regions of the specimen. The thick sections will be imaged at densities too low to beuseful (See also Chapters 7 & 16) and the thin sections, at densities too high to be viewed on theavailable illuminators. This principle is fully illustrated in Figure 22, which shows two radiographsof a steel stepped wedge, one (A) exposed at a high tube voltage and the other (B) at a lowvoltage. It is apparent that in the middle tones the differentiation in the steps is greater in the lowvoltageradiograph (B) than in the high-voltage radiograph (A). Near the end, however, the stepsshown in A are much less apparent in B.Figure 22: A: 220 kV exposure. B: 120 kV exposure. Radiographs of stell stepped wedgehaving a thickness range of 1/4 to 3/4 inch in 1/8-inch steps.Radiographic contrast is a result of both subject contrast and film contrast. Subject contrast isgoverned by the range of radiation intensities transmitted by the specimen. A flat sheet ofhomogeneous material of nearly uniform thickness would have very low subject contrast.Conversely, a specimen with large variations in thickness, which transmits a wide range ofRadiography in Modern Industry 35
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: kind of material radiographed, the
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
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

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?