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Introduction - Chapter 3
The broad definition of Industrial Radiography is as follows:
"The use of radiant energy in the form of X-rays or gamma rays for nondestructive examination of opaque objects, (e.g., ferrous and non-ferrous parts) in order to produce a radiograph (i.e., a photographic record) on radiographic films (densely, double coated). The "radiographic image" thus produced is used to locate internal flaws in the object being tested."
The term "Industrial Radiography" continues to be preferred and widely accepted by the professionals in the field. However it is important to note that the term "Industrial Radiography" is internationally preferred and accepted as it encompasses all newer radiographic techniques, neutron radiography and the related scientific principles.
Industrial Radiography utilizes an X-ray apparatus or the radioactive isotope as the source of X-rays or gamma-rays. These rays have the ability to penetrate matter. (Typical examples of matter are steel castings, human tissues, etc.). While penetrating through matter, these rays are selectively absorbed. This is dependent upon the matter's chemical composition, density, geometry of construction and thickness. Since the amount of radiation emerging from the opposite side (see Figure 3.1) of the object (or part) can be detected by means of a radiographic film, variations in this amount of emerging radiation create differing degrees of or radiographic film blackening, which in turn is related to the thickness of the object (or part).
Introduction - Chapter 4
The early X-ray tubes contained an amount of residual gases and consequently were known as "gas" tubes. They were inefficient and unreliable and susceptible even to small changes in the gas temperature or pressure. They were only capable of producing X-rays up to energies of about 130 kV.
In 1913, William David Coolidge developed a new X-ray tube. He found that tungsten had certain characteristics that made it a better target material than platinum. He first produced a ductile tungsten and then succeeded in vacuum casting copper around a tungsten disc. This greatly increased the heat conductivity of the anode which allowed for increased energy and a greater quantity of penetrating X-rays. Tungsten is now widely used for targets except in tubes built for special applications.
Dr. Coolidge's greatest contribution was discovering that an X-ray tube could be made to operate with consistency when a spiral filament of tungsten wire heated to incandescence by means of electric current was used in a vacuum tube. His first models operated at voltages of 140 kV - 200kV. There were the forerunners of the modern X-ray tube.
In order to produce even higher voltages, Dr. Coolidge developed in 1922, a sectional type of X-ray tube using what he called the Cascade principle. Voltages were applied to each section of the tube accelerating the electrons in steps. Using this principle he was able to produce a million volt X-ray tube.
Development of other necessary components of an X-ray apparatus was also continuing. Earlier shock-proof equipment had used oil in the casing as an insulator, however, it was found that Freon gas and later sulphur hexafluoride (SF6) pumped in under pressure was more efficient.
Concurrently, new types of iron core transformers were developed as well as those which eliminated the iron core used in the centre of the copper wire coils. New forms of rectifiers allowed for a greater X-ray output using alternating current. More efficient electrical circuits were developed and scientists, who were more knowledgeable of the structure of the atom and of the various particles of which it was formed, were completely involved in the production of modern X-ray apparatus.
Introduction - Chapter 5
Gamma rays are electromagnetic radiation similar to visible light or X-rays but of different wavelengths. This is shown in the sketch of the electromagnetic spectrum, Figure 2.2 of Chapter 2.
Atoms may be stable or unstable. A stable atom is one in which the arrangement of the constituent particles does not change and the atom does not lose any of its original particles. An unstable atom, referred to as a radioactive atom or radioisotope, attempts to become a stable atom by either a spontaneous rearrangement of particles, or by emitting particles from its nucleus with an accompanying loss of energy. In doing so, it changes to another type of atom of the same or a different element. Energy loss, in the continual rearrangement of particles, is radiated in the form of gamma rays.
Introduction - Chapter 6
In radiation work, it is necessary to understand the terminology and the units used for measuring different quantities relating to radioactivity, and to understand the interrelationships. The essential units and their definitions are described in the following sections. Even though some of the sections immediately following may appear to be repetitious, it is necessary to redefine and to reinforce these concepts in the context of radiation safety.
Introduction - Chapter 7
Meticulous housekeeping and attention to detail are the keynotes of good darkroom work. It is important, therefore, that considerable attention be given to the process involved in the development and fixation, to the establishment of a standardized working routine, to the care and maintenance of equipment and also to the ability to trace the origin of faults other than those directly related to errors in exposure. Approved darkroom practices begin with the planning and construction of the darkroom itself. The location, design and construction of the processing and film handling facilities are major factors in the establishment of radiographic services.
Introduction - Chapter 8
The technique used to radiograph a specimen generally refers to the sum total of all procedures, equipment and accessories used to examine it. This chapter deals primarily with the geometrical considerations, i.e., the positioning and orientation of the source of radiation energy, in relation to the specimen and the film. Each arrangement is unique to the shape of the specimen in question, its size, the material or materials of which it is composed, the section of specimen to be examined, its location in relation to other features and practical difficulties associated with obtaining a set-up that will provide an acceptable examination.
There are certain techniques or arrangements that can be considered fundamental to the geometry and size of the part regardless of its fabrication process or its end use. In this case we need not be concerned whether the specimen is, for example, a weld or a casting or an electrical component or a structure such as a nuclear plant. We need only to be concerned that the technique used complies with the standards or specifications relating to the end product. In some cases the geometry of the part may be peculiar to a specific component or structure. The radiographic technique must then be compatible with the product, and its end use.
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